android-滚动时获取RecycleView的中心可见项

这就是我要的:

enter image description here

如上图所示,我想在Rect上画一条中心线,然后在滚动时获得中心项(以及向左或向右移动)
这是我尝试绘制水平RecycleView的方法:

    HorizontalAdapter adapter = new HorizontalAdapter(data);
    LinearLayoutManager layoutManager
            = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
    recycleView.setLayoutManager(layoutManager);
    recycleView.setAdapter(adapter);

有什么方法可以知道哪个项目移动到2747082895838938138112的中心吗? 以及如何将RecycleView左右滚动一个位置?

更新:我试图使用滚动侦听器来获得中间位置,但是它不能用作外观。

  @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            int firstPos = layoutManager.findFirstVisibleItemPosition();
            int lastPos = layoutManager.findLastVisibleItemPosition();
            int middle = Math.abs(lastPos - firstPos) / 2 + firstPos;

            int selectedPos = -1;
            for (int i = 0; i < adapter.getItemCount(); i++) {
                if (i == middle) {
                    adapter.getItem(i).setSelected(true);
                    selectedPos = i;
                } else {
                    adapter.getItem(i).setSelected(false);
                }
            }

            adapter.notifyDataSetChanged();
        }

并得到结果:

enter image description here

我只想更改选定的项目(将文本更改为白色),当它处于蓝色Rect

R4j asked 2020-02-14T10:37:12Z
10个解决方案
50 votes

我做了这样的事情。 我完全可以满足您的需求。首先,这就是我的算法如何工作enter image description here

这是我的recyclerView适配器

public class DateAdapter extends RecyclerView.Adapter<DateAdapter.DateViewHolder> {
private ArrayList<LabelerDate> dateDataList;


private static final int VIEW_TYPE_PADDING = 1;
private static final int VIEW_TYPE_ITEM = 2;
private int paddingWidthDate = 0;

private int selectedItem = -1;

public DateAdapter(ArrayList<LabelerDate> dateData, int paddingWidthDate) {
    this.dateDataList = dateData;
    this.paddingWidthDate = paddingWidthDate;

}


@Override
public DateViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType == VIEW_TYPE_ITEM) {
        final View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_date,
                parent, false);
        return new DateViewHolder(view);
    } else {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_padding,
                parent, false);

        RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) view.getLayoutParams();
        layoutParams.width = paddingWidthDate;
        view.setLayoutParams(layoutParams);
        return new DateViewHolder(view);
    }
}

@Override
public void onBindViewHolder(DateViewHolder holder, int position) {
    LabelerDate labelerDate = dateDataList.get(position);
    if (getItemViewType(position) == VIEW_TYPE_ITEM) {
        if(labelerDate.dateType.equals(BirthDayActivity.DateType.C31))
                holder.tvDate.setText(String.valueOf(labelerDate.valueDate));
                holder.tvDate.setVisibility(View.VISIBLE);
                holder.imgSmall.setVisibility(View.VISIBLE);

        if (position == selectedItem) {
            holder.tvDate.setTextColor(Color.parseColor("#094673"));
            holder.tvDate.setTextSize(35);
            holder.imgSmall.setBackgroundResource(R.color.textviewbold);

        } else {
            holder.tvDate.setTextColor(Color.GRAY);
            holder.tvDate.setTextSize(35);
            holder.imgSmall.setBackgroundResource(R.color.gray);
        }
    }
}

public void setSelecteditem(int selecteditem) {
    this.selectedItem = selecteditem;
    notifyDataSetChanged();
}

@Override
public int getItemCount() {
    return dateDataList.size();
}

@Override
public int getItemViewType(int position) {
    LabelerDate labelerDate = dateDataList.get(position);
    if (labelerDate.dateType.equals(BirthDayActivity.DateType.NONE)) {
        return VIEW_TYPE_PADDING;
    }
    return VIEW_TYPE_ITEM;
}


public class DateViewHolder extends RecyclerView.ViewHolder {
    public TextView tvDate;
    public ImageView imgSmall;

    public DateViewHolder(View itemView) {
        super(itemView);
        tvDate = (TextView) itemView.findViewById(R.id.tvNumberDate);
        imgSmall = (ImageView) itemView.findViewById(R.id.small_marked_dob);
    }
}}

这是最重要的算法:

public void getRecyclerviewDate() {
    recyclerViewDate = (RecyclerView) findViewById(R.id.recyclerViewDay);
    ViewTreeObserver vtoDate = recyclerViewDate.getViewTreeObserver();
    vtoDate.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
        @Override
        public boolean onPreDraw() {
            recyclerViewDate.getViewTreeObserver().removeOnPreDrawListener(this);
            finalWidthDate = recyclerViewDate.getMeasuredWidth();
            itemWidthDate = getResources().getDimension(R.dimen.item_dob_width);
            paddingDate = (finalWidthDate - itemWidthDate) / 2;
            firstItemWidthDate = paddingDate ;
            allPixelsDate = 0;

            final LinearLayoutManager dateLayoutManager = new LinearLayoutManager(getApplicationContext());
            dateLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
            recyclerViewDate.setLayoutManager(dateLayoutManager);
            recyclerViewDate.addOnScrollListener(new RecyclerView.OnScrollListener() {
                @Override
                public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                    super.onScrollStateChanged(recyclerView, newState);
                    synchronized (this) {
                         if(newState == RecyclerView.SCROLL_STATE_IDLE){           
                            calculatePositionAndScrollDate(recyclerView);
                        }
                    }

                }

                @Override
                public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                    super.onScrolled(recyclerView, dx, dy);
                    allPixelsDate += dx;
                }
            });
            if (labelerDates == null)
                labelerDates = new ArrayList<>();
            labelerDates.addAll(genLabelerDate(currentMonth, currentYear));
            dateAdapter = new DateAdapter(labelerDates, (int) firstItemWidthDate);
            recyclerViewDate.setAdapter(dateAdapter);
            return true;
        }
    });
}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/

private void calculatePositionAndScrollDate(RecyclerView recyclerView) {
    int expectedPositionDate = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);

    if (expectedPositionDate == -1) {
        expectedPositionDate = 0;
    } else if (expectedPositionDate >= recyclerView.getAdapter().getItemCount() - 2) {
        expectedPositionDate--;
    }
    scrollListToPositionDate(recyclerView, expectedPositionDate);

}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
private void scrollListToPositionDate(RecyclerView recyclerView, int expectedPositionDate) {
    float targetScrollPosDate = expectedPositionDate * itemWidthDate + firstItemWidthDate - paddingDate;
    float missingPxDate = targetScrollPosDate - allPixelsDate;
    if (missingPxDate != 0) {
        recyclerView.smoothScrollBy((int) missingPxDate, 0);
    }
}
private void setDateValue() {
    int expectedPositionDateColor = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
    setColorDate = expectedPositionDateColor + 1;
    //set color here
    dateAdapter.setSelecteditem(setColorDate);
}
 @Override
protected void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);   
    allPixelsDate = savedInstanceState.getFloat(BUNDLE_LIST_PIXELS_DATE);
    allPixelsDateChanged = savedInstanceState.getFloat(BUNDLE_LIST_PIXELS_DATE_CHANGED);
}

@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putFloat(BUNDLE_LIST_PIXELS_DATE, allPixelsDate);
    outState.putFloat(BUNDLE_LIST_PIXELS_DATE_CHANGED, allPixelsDateChanged);
}

这是我的结果:enter image description here

看这个视频链接,这是我的应用程序演示

TranHieu answered 2020-02-14T10:37:37Z
11 votes

有时需要将整个示例代码块放在一起,因为我们可能会遗漏一些东西。 这就是我所拥有的,可以随时纠正任何问题,因为我可能在某个地方犯了一些小错误。 是的,这个答案是@tranhieu答案的扩展。 谢谢@tranhieu。

MainActivity.java

package com.test;

import android.app.Activity;
import android.graphics.Color;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.TextView;

import java.util.ArrayList;

public class MainActivity extends Activity {

    private static final String TAG = MainActivity.class.getSimpleName();

    public float firstItemWidthDate;
    public float paddingDate;
    public float itemWidthDate;
    public int allPixelsDate;
    public int finalWidthDate;
    private DateAdapter dateAdapter;
    private ArrayList<LabelerDate> labelerDates = new ArrayList<>();

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getRecyclerviewDate();

    }


    public void getRecyclerviewDate() {
        final RecyclerView recyclerViewDate = (RecyclerView) findViewById(R.id.rv_tasks_date);
        if (recyclerViewDate != null) {
            recyclerViewDate.postDelayed(new Runnable() {
                @Override
                public void run() {
                    setDateValue();
                }
            }, 300);
            recyclerViewDate.postDelayed(new Runnable() {
                @Override
                public void run() {
                    recyclerViewDate.smoothScrollToPosition(dateAdapter.getItemCount()-1);
                    setDateValue();
                }
            }, 5000);
        }
        ViewTreeObserver vtoDate = recyclerViewDate.getViewTreeObserver();
        vtoDate.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {


            @Override
            public boolean onPreDraw() {
                recyclerViewDate.getViewTreeObserver().removeOnPreDrawListener(this);
                finalWidthDate = recyclerViewDate.getMeasuredWidth();
                itemWidthDate = getResources().getDimension(R.dimen.item_dob_width);
                paddingDate = (finalWidthDate - itemWidthDate) / 2;
                firstItemWidthDate = paddingDate;
                allPixelsDate = 0;

                final LinearLayoutManager dateLayoutManager = new LinearLayoutManager(getApplicationContext());
                dateLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
                recyclerViewDate.setLayoutManager(dateLayoutManager);
                recyclerViewDate.addOnScrollListener(new RecyclerView.OnScrollListener() {
                    @Override
                    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                        super.onScrollStateChanged(recyclerView, newState);
                        synchronized (this) {
                            if (newState == RecyclerView.SCROLL_STATE_IDLE) {
                                calculatePositionAndScrollDate(recyclerView);
                            }
                        }

                    }

                    @Override
                    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                        super.onScrolled(recyclerView, dx, dy);
                        allPixelsDate += dx;
                    }
                });
                if (labelerDates == null) {
                    labelerDates = new ArrayList<>();
                }
                genLabelerDate();
                dateAdapter = new DateAdapter(labelerDates, (int) firstItemWidthDate);
                recyclerViewDate.setAdapter(dateAdapter);
                dateAdapter.setSelecteditem(dateAdapter.getItemCount() - 1);
                return true;
            }
        });
    }

    private void genLabelerDate() {
        for (int i = 0; i < 32; i++) {
            LabelerDate labelerDate = new LabelerDate();
            labelerDate.setNumber(Integer.toString(i));
            labelerDates.add(labelerDate);

            if (i == 0 || i == 31) {
                labelerDate.setType(DateAdapter.VIEW_TYPE_PADDING);
            } else {
                labelerDate.setType(DateAdapter.VIEW_TYPE_ITEM);
            }
        }
    }
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/

    private void calculatePositionAndScrollDate(RecyclerView recyclerView) {
        int expectedPositionDate = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);

        if (expectedPositionDate == -1) {
            expectedPositionDate = 0;
        } else if (expectedPositionDate >= recyclerView.getAdapter().getItemCount() - 2) {
            expectedPositionDate--;
        }
        scrollListToPositionDate(recyclerView, expectedPositionDate);

    }

    /* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
    private void scrollListToPositionDate(RecyclerView recyclerView, int expectedPositionDate) {
        float targetScrollPosDate = expectedPositionDate * itemWidthDate + firstItemWidthDate - paddingDate;
        float missingPxDate = targetScrollPosDate - allPixelsDate;
        if (missingPxDate != 0) {
            recyclerView.smoothScrollBy((int) missingPxDate, 0);
        }
        setDateValue();
    }

    //
    private void setDateValue() {
        int expectedPositionDateColor = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
        int setColorDate = expectedPositionDateColor + 1;
//        set color here
        dateAdapter.setSelecteditem(setColorDate);
    }


    public class DateAdapter extends RecyclerView.Adapter<DateAdapter.DateViewHolder> {
        private ArrayList<LabelerDate> dateDataList;


        private static final int VIEW_TYPE_PADDING = 1;
        private static final int VIEW_TYPE_ITEM = 2;
        private int paddingWidthDate = 0;

        private int selectedItem = -1;

        public DateAdapter(ArrayList<LabelerDate> dateData, int paddingWidthDate) {
            this.dateDataList = dateData;
            this.paddingWidthDate = paddingWidthDate;

        }


        @Override
        public DateViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            if (viewType == VIEW_TYPE_ITEM) {
                final View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item,
                    parent, false);
                return new DateViewHolder(view);
            } else {
                View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item,
                    parent, false);

                RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) view.getLayoutParams();
                layoutParams.width = paddingWidthDate;
                view.setLayoutParams(layoutParams);
                return new DateViewHolder(view);
            }
        }

        @Override
        public void onBindViewHolder(DateViewHolder holder, int position) {
            LabelerDate labelerDate = dateDataList.get(position);
            if (getItemViewType(position) == VIEW_TYPE_ITEM) {
                holder.tvDate.setText(labelerDate.getNumber());
                holder.tvDate.setVisibility(View.VISIBLE);

                Log.d(TAG, "default " + position + ", selected " + selectedItem);
                if (position == selectedItem) {
                    Log.d(TAG, "center" + position);
                    holder.tvDate.setTextColor(Color.parseColor("#76FF03"));
                    holder.tvDate.setTextSize(35);

                } else {
                    holder.tvDate.setTextColor(Color.WHITE);
                    holder.tvDate.setTextSize(18);
                }
            } else {
                holder.tvDate.setVisibility(View.INVISIBLE);
            }
        }

        public void setSelecteditem(int selecteditem) {
            this.selectedItem = selecteditem;
            notifyDataSetChanged();
        }

        @Override
        public int getItemCount() {
            return dateDataList.size();
        }

        @Override
        public int getItemViewType(int position) {
            LabelerDate labelerDate = dateDataList.get(position);
            if (labelerDate.getType() == VIEW_TYPE_PADDING) {
                return VIEW_TYPE_PADDING;
            } else {
                return VIEW_TYPE_ITEM;
            }

        }


        public class DateViewHolder extends RecyclerView.ViewHolder {
            public TextView tvDate;

            public DateViewHolder(View itemView) {
                super(itemView);
                tvDate = (TextView) itemView.findViewById(R.id.txt_date);
            }
        }
    }

    private class LabelerDate {
        private int type;
        private String number;

        public String getNumber() {
            return number;
        }

        public void setNumber(String number) {
            this.number = number;
        }

        public int getType() {
            return type;
        }

        public void setType(int type) {
            this.type = type;
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical">

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <android.support.v7.widget.RecyclerView
            android:id="@+id/rv_tasks_date"
            android:layout_width="match_parent"
            android:layout_height="48dp" />

        <ImageView
            android:layout_width="48dp"
            android:layout_height="48dp"
            android:layout_gravity="center"
            android:layout_marginTop="48dp"
            android:src="@android:drawable/ic_dialog_info" />
    </FrameLayout>

</LinearLayout>

item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical" android:layout_width="wrap_content"
              android:layout_height="match_parent">

    <TextView
        android:id="@+id/txt_date"
        android:layout_width="@dimen/item_dob_width"
        android:layout_height="48dp"
        android:text="32"
        android:textColor="@android:color/white"
        android:background="@android:color/darker_gray"
        android:textSize="28sp"
        android:gravity="center"/>

</LinearLayout>

dimens.xml

<resources>
    <dimen name="item_dob_width">100dp</dimen>
</resources>
silentsudo answered 2020-02-14T10:38:17Z
5 votes

我在这里使用了SnapHelper:

    // init snaphelper        
    SnapHelper snapHelper = new LinearSnapHelper();
    snapHelper.attachToRecyclerView(recyclerView)

    // init layout manager
    LinearLayoutManager layoutManager = new LinearLayoutManager(mainActivity);
    layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
    recyclerView.setLayoutManager(layoutManager);

    // init adapter
    adatper.setSnapHelper(snapHelper);
    adatper.setLayoutManager(layoutManager);

    adatper.initAdapter(new Float((DisplayHelper.getDisplayWidth(mainActivity) / 2) - (fooViewWidth / 2)).intValue());
    recyclerView.setAdapter(adatper);

正如TranHieu所说,插入2个用于填充的项目(在开始和结束位置)的解决方案是好的。

由于代码的可读性差,我不喜欢使用ViewTreeObserver。 如果回收了这些物品,那么您还必须使用这种技术来管理它们的重新绘制。

如果使用的是customview类,则可以直接在这些类中设置其宽度。

例如这是我的补习班

/**
 * Created by firegloves on 25/09/15.
 */
@EViewGroup(R.layout.view_padding)
public class PaddingView extends FooView {

    Context mCtx;

    public PaddingView(Context context) {
        super(context);
        mCtx = context;
    }


    public void setWidth(int width) {
        setLayoutParams(new LayoutParams(width, ViewGroup.LayoutParams.WRAP_CONTENT));
    }

}

在我的适配器中,我存储了所需的填充项目宽度,该宽度等于(displayWidth / 2)-(realItemWidth / 2)

这是我的适配器,不要看与RecyclerView.Adapter不匹配的方法,要注意initAdapter方法和onCreateItemView方法

@EBean
public class FooAdapterRecycler extends RecyclerViewAdapterBase<Foo, FooView> {

    private final int TYPE_PADDING_VIEW = 0;
    private final int TYPE_REAL_VIEW = 1;

    @RootContext
    Context ctx;
    @Bean(Finder.class)
    IFinder finder;

    SnapHelper snapHelper;
    RecyclerView.LayoutManager layoutManager;

    private int paddingWidth = 0;

    /**
     * preleva i dati dal finder
     */
    public void initAdapter(int paddingWidth) {

        /*******************************
         * THIS CODE IS THE IMPORTANT ONE
         ******************************/

        this.paddingWidth = paddingWidth;

        // add 1 item for initial space
        mItems = new ArrayList<>();
        Foo foo = new Foo();
        mItems.add(foo);

        // get real items from finder
        mItems.addAll(finder.findAll());

        // add 1 item for final space
        mItems = new ArrayList<>();
        Foo foo2 = new Foo();
        mItems.add(foo2);

    }


    @Override
    public int getItemViewType(int position) {
        if (position == 0 || position == getItemCount()-1) {
            return TYPE_PADDING_VIEW;
        } else {
            return TYPE_REAL_VIEW;
        }
    }

    @Override
    protected FooView onCreateItemView(ViewGroup parent, int viewType) {

        /*******************************
         * THIS CODE IS THE IMPORTANT ONE
         ******************************/

        if (viewType == TYPE_PADDING_VIEW) {
            PaddingView view = PaddingView_.build(ctx);
            view.setWidth(paddingWidth);
            return view;
        } else {
            return FooView_.build(ctx);
        }
    }

    public void setSnapHelper(SnapHelper snapHelper) {
        this.snapHelper = snapHelper;
    }

    public void setLayoutManager(RecyclerView.LayoutManager layoutManager) {
        this.layoutManager = layoutManager;
    }
}

我正在使用AndroidAnnotations库,但这不是必需的

希望能有所帮助

firegloves answered 2020-02-14T10:39:16Z
3 votes

如另一个答案中所述,没有直接的方法可以做到这一点。

这可能是您可以实现问题中所描述的方法。

  1. 了解屏幕上可见的项目数。
  2. 每次滚动视图时,以编程方式选择中间项。
  3. 在recyclerview的中间项目上保留部分透明的图像作为覆盖。 (您需要根据回收站视图的宽度或屏幕的宽度以及您选择放置的叠加图像的宽度来计算坐标。
  4. 每次滚动时,在回收者视图下方的文本视图中刷新所选值。

图像叠加层必须以看起来好像已连接的方式放置,并作为一个控件放置。

AndroidMechanic - Viral Patel answered 2020-02-14T10:40:04Z
3 votes

好家伙。 我一直在寻找这个答案将近一个星期,然后找到了解决方案。 自定义SnapHelperRecylcerView吗? 不。

这是最简单的方法:

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:paddingStart="150dp"
    android:paddingEnd="150dp"
    android:clipToPadding="false" />

关键部分是:

    android:paddingStart="150dp"
    android:paddingEnd="150dp"
    android:clipToPadding="false"

然后只需将SnapHelper分配给您的RecylcerView

val snapHelper = LinearSnapHelper()
snapHelper.attachToRecyclerView(recyclerView)

就是这个。 最简单,最完美的解决方案

egorikem answered 2020-02-14T10:40:42Z
2 votes

使用快照程序-更流畅的解决方案

这是使用SnapHelper的另一种解决方案。 从@TranHieu的答案开始:

[https://stackoverflow.com/a/34647005/3944251]

和@ sector11压缩在这里:

[https://stackoverflow.com/a/38411582/3944251]

我编写了以下基于以上两个答案的代码,但它更简单,并且使用android支持库24.2.0中提供的SnapHelper提供了更平滑的解决方案。

在这里,您具有MainActivity类。 其余与@ sector11的答案相同。

import android.graphics.Color;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.LinearSnapHelper;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.TextView;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = MainActivity.class.getSimpleName();

    public float firstItemWidthDate;
    public float itemWidthDate;
    public int allPixelsDate;
    public int finalWidthDate;
    private DateAdapter dateAdapter;
    private ArrayList<LabelerDate> labelerDates;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        labelerDates = new ArrayList<>();
        getRecyclerviewDate();

    }


    public void getRecyclerviewDate() {
        final RecyclerView recyclerViewDate = (RecyclerView) findViewById(R.id.rv_tasks_date);
        recyclerViewDate.postDelayed(new Runnable() {
            @Override
            public void run() {
                //recyclerViewDate.smoothScrollToPosition(dateAdapter.getItemCount()-1);
                setDateValue();
            }
        }, 300);
        ViewTreeObserver vtoDate = recyclerViewDate.getViewTreeObserver();
        vtoDate.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {

            @Override
            public boolean onPreDraw() {
                recyclerViewDate.getViewTreeObserver().removeOnPreDrawListener(this);
                finalWidthDate = recyclerViewDate.getMeasuredWidth();
                itemWidthDate = getResources().getDimension(R.dimen.item_dob_width);
                firstItemWidthDate = (finalWidthDate - itemWidthDate) / 2;
                allPixelsDate = 0;

                final LinearLayoutManager dateLayoutManager = new LinearLayoutManager(getApplicationContext());
                dateLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
                recyclerViewDate.setLayoutManager(dateLayoutManager);

                /* Create a LinearSnapHelper and attach the recyclerView to it. */
                final LinearSnapHelper snapHelper = new LinearSnapHelper();
                snapHelper.attachToRecyclerView(recyclerViewDate);

                recyclerViewDate.addOnScrollListener(new RecyclerView.OnScrollListener() {
                    @Override
                    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                        allPixelsDate += dx;
                        recyclerView.post(new Runnable() {
                            public void run() {
                                setDateValue();
                            }
                        });
                    }
                });

                genLabelerDate();
                dateAdapter = new DateAdapter(labelerDates, (int) firstItemWidthDate);
                recyclerViewDate.setAdapter(dateAdapter);
                dateAdapter.setSelecteditem(dateAdapter.getItemCount() - 1);
                return true;
            }
        });
    }

    private void genLabelerDate() {
        for (int i = 0; i < 32; i++) {
            LabelerDate labelerDate = new LabelerDate();
            labelerDate.setNumber(Integer.toString(i));
            labelerDates.add(labelerDate);

            if (i == 0 || i == 31) {
                labelerDate.setType(DateAdapter.VIEW_TYPE_PADDING);
            } else {
                labelerDate.setType(DateAdapter.VIEW_TYPE_ITEM);
            }
        }
    }

    //
    private void setDateValue() {
        int expectedPositionDateColor = Math.round(allPixelsDate / itemWidthDate);
        int setColorDate = expectedPositionDateColor + 1;
//        set color here
        dateAdapter.setSelecteditem(setColorDate);
    }


    public class DateAdapter extends RecyclerView.Adapter<DateAdapter.DateViewHolder> {
        private ArrayList<LabelerDate> dateDataList;


        private static final int VIEW_TYPE_PADDING = 1;
        private static final int VIEW_TYPE_ITEM = 2;
        private int paddingWidthDate = 0;

        private int selectedItem = -1;

        public DateAdapter(ArrayList<LabelerDate> dateData, int paddingWidthDate) {
            this.dateDataList = dateData;
            this.paddingWidthDate = paddingWidthDate;

        }


        @Override
        public DateAdapter.DateViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false);
            if (viewType == VIEW_TYPE_PADDING) {
                RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) view.getLayoutParams();
                layoutParams.width = paddingWidthDate;
                view.setLayoutParams(layoutParams);
            }
            return new DateViewHolder(view);
        }

        @Override
        public void onBindViewHolder(DateAdapter.DateViewHolder holder, int position) {
            LabelerDate labelerDate = dateDataList.get(position);
            if (getItemViewType(position) == VIEW_TYPE_ITEM) {
                holder.tvDate.setText(labelerDate.getNumber());
                holder.tvDate.setVisibility(View.VISIBLE);

                Log.d(TAG, "default " + position + ", selected " + selectedItem);
                if (position == selectedItem) {
                    Log.d(TAG, "center" + position);
                    holder.tvDate.setTextColor(Color.parseColor("#76FF03"));
                    holder.tvDate.setTextSize(35);

                } else {
                    holder.tvDate.setTextColor(Color.WHITE);
                    holder.tvDate.setTextSize(18);
                }
            } else {
                holder.tvDate.setVisibility(View.INVISIBLE);
            }
        }

        public void setSelecteditem(int selecteditem) {
            this.selectedItem = selecteditem;
            notifyDataSetChanged();
        }

        @Override
        public int getItemCount() {
            return dateDataList.size();
        }

        @Override
        public int getItemViewType(int position) {
            LabelerDate labelerDate = dateDataList.get(position);
            if (labelerDate.getType() == VIEW_TYPE_PADDING) {
                return VIEW_TYPE_PADDING;
            } else {
                return VIEW_TYPE_ITEM;
            }

        }


        public class DateViewHolder extends RecyclerView.ViewHolder {
            public TextView tvDate;

            public DateViewHolder(View itemView) {
                super(itemView);
                tvDate = (TextView) itemView.findViewById(R.id.txt_date);
            }
        }
    }

    private class LabelerDate {
        private int type;
        private String number;

        public String getNumber() {
            return number;
        }

        public void setNumber(String number) {
            this.number = number;
        }

        public int getType() {
            return type;
        }

        public void setType(int type) {
            this.type = type;
        }
    }
}
Dionis Beqiraj answered 2020-02-14T10:41:28Z
1 votes

对于此功能,请使用EcoGallery库:[https://github.com/falnatsheh/EcoGallery]

user3579059 answered 2020-02-14T10:41:49Z
0 votes

起初,我需要类似的东西,不是这个。 但是我能够根据自己的需要调整@TranHieu解决方案,因此我投票支持他的解决方案。

我想创建全屏水平recyclerview,在用户滚动更新后将Position滚动到mostVisibleItem。

设定:

private void setUpScrolling() {
    mRecyclerVIew.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
        @Override
        public boolean onPreDraw() {
            mRecyclerVIew.getViewTreeObserver().removeOnPreDrawListener(this);
            CustomScrollListener listener = (CustomScrollListener) mScrollListener;
            listener.width = mRecyclerVIew.getMeasuredWidth();
            listener.dx = 0;
            return true;
        }
    });
}

听众:

private class CustomScrollListener extends OnScrollListener {
    private int mLastDx = 0;
    int width = 0;
    int dx = 0;

    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        if (newState == RecyclerView.SCROLL_STATE_IDLE) {
            if (mLastDx != dx) {
                scrollToMostVisibleItem();
            } else {
                dx = 0;
                mLastDx = 0;
            }
        }
        super.onScrollStateChanged(recyclerView, newState);
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        this.dx += dx;
    }

    private void scrollToMostVisibleItem() {
        int direction = (dx > 0) ? 1 : -1;
        dx = Math.abs(dx);
        int shiftCount = Math.round(dx / width);
        int pixelShift = dx % width;
        if (pixelShift > width / 2) {
            shiftCount++;
        }

        float targetScrollPixels = shiftCount * width;
        float finalScrollPixels = (targetScrollPixels - dx) * direction;
        if (finalScrollPixels != 0) {
            mRecyclerVIew.smoothScrollBy((int) finalScrollPixels, 0);
            mLastDx = (int) finalScrollPixels;
            dx = 0;
        }
    }
}
ThinkDeep answered 2020-02-14T10:42:22Z
0 votes

在我的情况下,我使用了另一种方法。

您可以在此处找到详细信息:RecyclerView-如何在滚动1时突出显示中央可见项目

我认为,我的解决方案比其他解决方案更容易。

eldivino87 answered 2020-02-14T10:42:51Z
0 votes

如果有人正在寻找更通用的实现,这是基于此线程的答案的我的代码:

添加CenterLinearSnapHelper

public class CenterLinearSnapHelper extends LinearSnapHelper {

    //Constants
    public static final String TAG = CenterLinearSnapHelper.class.getSimpleName();

    //Attributes
    private Context context;
    private float itemWidth;
    private OnPaddingComputationListener listener;

    //Constructors

    /**
     * A linear snap helper which helps centering the items in a recyclerview.
     *
     * @param itemWidth The (fixed) width of a child view in pixels.
     */
    public CenterLinearSnapHelper(float itemWidth) {
        this.itemWidth = itemWidth;
    }

    public void attachToRecyclerView(@Nullable RecyclerView recyclerView,
                                     @NonNull OnPaddingComputationListener listener) throws IllegalStateException {
        this.listener = listener;

        //Calculates the padding for the first and end item
        calculatePadding(recyclerView);

        //Create a LinearSnapHelper and attach the recyclerView to it.
        attachToRecyclerView(recyclerView);
    }

    public float getItemWidth() {
        return itemWidth;
    }

    private void calculatePadding(RecyclerView recyclerView) {
        if (recyclerView == null)
            return;

        ViewTreeObserver observer = recyclerView.getViewTreeObserver();
        observer.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {

            @Override
            public boolean onPreDraw() {
                recyclerView.getViewTreeObserver().removeOnPreDrawListener(this);
                int finalWidth = recyclerView.getMeasuredWidth();
                float padding = (finalWidth - itemWidth) / 2;
                listener.onPadding(padding, finalWidth);
                return true;
            }
        });
    }

    public interface OnPaddingComputationListener {
        void onPadding(float padding, int finalWidth);
    }

}

在创建RecyclerView的活动/片段中:

float itemWidth = getResources().getDimension(R.dimen.favorite_room_width);
CenterLinearSnapHelper snapHelper = new CenterLinearSnapHelper(itemWidth);
snapHelper.attachToRecyclerView(binding.listFavorites, (padding, finalWidth) -> {
    //Set the adapter
    roomAdapter = new RoomAdapter(requireContext(), rooms);
    roomAdapter.addPaddingItems((int) padding);
    roomAdapter.setOnToggleClickListener(FavoritesFragment.this);
    binding.listFavorites.setAdapter(roomAdapter);
});

在您的适配器中:

public void addPaddingItems(int padding) {
    if (padding < 0)
        throw new IllegalStateException("Padding cannot be smaller than 0");

    this.padding = padding;
    //Add 2 new items as the first and last
    //NOTE: If you update your existing dataset (e.g add new items), you should redo the calculation!
    rooms.add(0, new Room("First"));
    rooms.add(rooms.size(), new Room("Last"));
}


@Override
public int getItemViewType(int position) {
    if (padding >= 0 && (position == 0 || position == rooms.size() - 1)) {
        return VIEW_TYPE_PADDING;
    }

    return VIEW_TYPE_ITEM;
}

@NonNull
@Override
public RoomViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    ViewFavoriteRoomBinding binding = DataBindingUtil.inflate(inflater, R.layout.view_favorite_room, parent, false);

    if (viewType == VIEW_TYPE_PADDING) {
        RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) binding.getRoot().getLayoutParams();
        layoutParams.width = padding;
        binding.getRoot().setLayoutParams(layoutParams);
    }

    RoomViewHolder viewHolder = new RoomViewHolder(context, binding, onToggleClickListener);
    viewHolder.getRecyclerView().setRecycledViewPool(viewPool);
    return viewHolder;
}
Verhelst answered 2020-02-14T10:43:24Z
translate from https://stackoverflow.com:/questions/34586637/get-center-visible-item-of-recycleview-when-scrolling