android - linearLayoutmaneger.findLastCompletelyVisibleItemPosition 在 coordinatorLayout 中返回错误值

Question

我在 coordinatorLayout 中有一个 recyclerView，我想从中获取最后一个可见的项目:

<?xml version="1.0" encoding="utf-8"?><android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<android.support.design.widget.AppBarLayout
    android:id="@+id/appbarLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/colorPrimary"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    >

    <android.support.design.widget.CollapsingToolbarLayout
        android:id="@+id/main.collapsing"
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:background="#f00"
        app:layout_scrollFlags="scroll|exitUntilCollapsed">

    </android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>

<android.support.v7.widget.RecyclerView
    android:scrollbars="none"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    android:id="@+id/recyclerView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/lastVisibleItem"
    android:text="last position"
    />


 </android.support.design.widget.CoordinatorLayout>

和

findViewById(R.id.lastVisibleItem).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            int position=((LinearLayoutManager) mRecyclerView.getLayoutManager()).findLastCompletelyVisibleItemPosition();

            Log.d(TAG, "onClick: position="+position);
            Toast.makeText(RecyclerViewActivity.this, "position="+position, Toast.LENGTH_SHORT).show();
        }
    });

问题是在开始 findLastCompletelyVisibleItemPosition() 方法返回时，例如，14 是错误的，12 是正确的，在我向下滚动到第 14 项后，findLastCompletelyVisibleItemPosition()再次返回 14。
我知道这是因为 AppBarLayout 和 CoordinatorLayout 但我找不到正确的方法来找出最后一个完整的可见项目位置是什么。

Answer 1

我已经设法找到解决此问题的方法

您应该为您的 RecyclerView 使用自定义 LayoutManager 并覆盖查找第一个和最后一个位置的方法

public final class FixedForAppBarLayoutManager extends LinearLayoutManager {

public FixedForAppBarLayoutManager(final Context context, final AttributeSet attrs, final int defStyleAttr, final int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
}

public FixedForAppBarLayoutManager(final Context context, final int spanCount) {
    super(context, spanCount);
}

public FixedForAppBarLayoutManager(final Context context, final int spanCount, final int orientation, final boolean reverseLayout) {
    super(context, spanCount, orientation, reverseLayout);
}

@Override
public int findFirstVisibleItemPosition() {
    final View item = findVisibleItem(0, getChildCount(), false);
    return item == null ? -1 : getPosition(item);
}

@Override
public int findFirstCompletelyVisibleItemPosition() {
    final View item = findVisibleItem(0, getChildCount(), true);
    return item == null ? -1 : getPosition(item);
}

@Override
public int findLastVisibleItemPosition() {
    final View item = findVisibleItem(getChildCount() - 1, -1, false);
    return item == null ? -1 : getPosition(item);
}

@Override
public int findLastCompletelyVisibleItemPosition() {
    final View item = findVisibleItem(getChildCount() - 1, -1, true);
    return item == null ? -1 : getPosition(item);
}

private View findVisibleItem(final int fromIndex, final int toIndex, final boolean isCompletely) {
    final int next = toIndex > fromIndex ? 1 : -1;
    for (int i = fromIndex; i != toIndex; i += next) {
        final View child = getChildAt(i);
        if (checkIsVisible(child, isCompletely)) {
            return child;
        }
    }

    return null;
}

private boolean checkIsVisible(final View child, final boolean isCompletely) {
    final int[] location = new int[2];
    child.getLocationOnScreen(location);

    final View parent = (View) child.getParent();
    final Rect parentRect = new Rect();
    parent.getGlobalVisibleRect(parentRect);

    if (getOrientation() == HORIZONTAL) {
        final int childLeft = location[0];
        final int childRight = location[0] + child.getWidth();
        return isCompletely
            ? childLeft >= parentRect.left && childRight <= parentRect.right
            : childLeft <= parentRect.right && childRight >= parentRect.left;
    } else {
        final int childTop = location[1];
        final int childBottom = location[1] + child.getHeight();
        return isCompletely
            ? childTop >= parentRect.top && childBottom <= parentRect.bottom
            : childTop <= parentRect.bottom && childBottom >= parentRect.top;
    }
}