android - 在 RecyclerView ItemDecoration.getItemOffsets 中获取 subview 高度

Question

我正在尝试创建一个 ItemDecoration，它将通过向最后一个项目动态添加填充来保持 RecyclerView 的最小高度。

要计算填充量，我需要知道所有 child 的总高度。我通过获取单个 View 的高度并将其乘以适配器中的项目数来对此进行近似。

我遇到的问题是 view.getHeight() 并不总是返回正确的高度。通常第一次调用 getItemOffsets() 时高度比它应该的小很多(例如 30px vs 300px)。即使我在布局 XML 中为 subview 提供固定高度，也会发生这种情况。我猜这与测量/布局周期有关，因为我不确定如何在 ItemDecoration 中获得正确的 View 尺寸。

在 getItemOffsets() 中以编程方式获取 subview 高度的正确方法是什么？

元素装饰:

public class MinHeightPaddingItemDecoration extends RecyclerView.ItemDecoration {
    private static final String LOG_TAG = MinHeightPaddingItemDecoration.class.getSimpleName();

    private int mMinHeight;

    public MinHeightPaddingItemDecoration(int minHeight) {
        super();
        mMinHeight = minHeight;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView recyclerView, RecyclerView.State state) {
        int itemCount = state.getItemCount();
        int lastPosition = itemCount - 1;
        int itemPosition = recyclerView.getChildAdapterPosition(view);
        int layoutPosition = recyclerView.getChildLayoutPosition(view);

        // If this view isnt on screen then do nothing
        if (layoutPosition != RecyclerView.NO_POSITION && itemPosition == lastPosition) {

            // NOTE: view.getHeight() doesn't always return the correct height, even if the layout is given a fixed height in the XML
            int childHeight = view.getHeight();

            int totalChildHeight = childHeight * itemCount;

            int minHeight = getMinHeight();
            if (totalChildHeight < minHeight) {
                outRect.bottom = minHeight - totalChildHeight;
            }
        }
    }

    private int getMinHeight() {
        return mMinHeight;
    }
}

recycler_view_item.xml

<?xml version="1.0" encoding="utf-8"?>
<layout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">
    <data>
        <variable name="controller" type="my.ViewController"/>
    </data>

    <android.support.v7.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:layout_gravity="center"
        android:clickable="true"
        android:onClick="@{() -> controller.doSomething()}">

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">
                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:text="Child layout"
                    />
        </RelativeLayout>

    </android.support.v7.widget.CardView>
</layout>

Answer 1

我找到了固定大小的 subview 的解决方法。我仍然不确定如何处理动态大小的布局。

// NOTE: view.getHeight() doesn't always return the correct height 
// NOTE: even if the layout is given a fixed height in the XML. 
// NOTE: Instead directly access the LayoutParams height value
int childHeight = view.getLayoutParams().height;