Bug系列：RecycleView中高度使用wrap_conte

一. 问题描述：

项目中在使用RecycleView的时候，为它设置了高度 wrap_content 或 match_parent， 但是RecycleView中的Item 没有显示。

二. 我的解决方式：

简单粗暴的解决方法， 我把RecycleView的高度限定死了，给它一个固定的值(比如： 100dp)。这样RecycleView中的Item就会显示出来。 但是这样的方式不能解决根本问题。

三.探索根本原因，找到解决方法：

在使用RecycleView的时候我们都会注意到

RecyclerView recyclerView = findViewById(R.id.recycle_view);
RecyclerView.LayoutManager lmanager = new LinearLayoutManager(this, RecyclerView.VERTICAL, true);
//GridLayoutManager  gmanager = new GridLayoutManager(this, 3);
 ManageAddressAdapter adapter = new ManageAddressAdapter(this, allAddresses);
 recyclerView.setLayoutManager(lmanager);
 recyclerView.setAdapter(adapter);

我们经常使用系统提供的 LinearLayoutManager，GridLayoutManager
，StaggeredGridLayoutManager 布局管理器。它们是管理RecycleView中Item子布局显示测量，定位等。根本原因就是管理器导致的(源码还没有具体研究)

解决方法：写一个自己的MyLayoutManager 重写onMeasure()测量方法

public class MyLinearLayoutManager extends LinearLayoutManager {
 
    private static final String TAG = MyLinearLayoutManager.class.getSimpleName();
 
    public MyLinearLayoutManager(Context context) {
        super(context);
    }
 
    public MyLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
        super(context, orientation, reverseLayout);
    }
 
    private int[] mMeasuredDimension = new int[2];
 
    @Override
    public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state,
                          int widthSpec, int heightSpec) {
        //宽度模式， 高度模式
        final int widthMode = View.MeasureSpec.getMode(widthSpec);
        final int heightMode = View.MeasureSpec.getMode(heightSpec);
       // 宽高的测量尺寸
        final int widthSize = View.MeasureSpec.getSize(widthSpec);
        final int heightSize = View.MeasureSpec.getSize(heightSpec);
        int width = 0;
        int height = 0;
        for (int i = 0; i < getItemCount(); i++) {
            measureScrapChild(recycler, i,
                    View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
                    View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
                    mMeasuredDimension);
 
            if (getOrientation() == HORIZONTAL) {
                width = width + mMeasuredDimension[0];
                if (i == 0) {
                    height = mMeasuredDimension[1];
                }
            } else {
                height = height + mMeasuredDimension[1];
                if (i == 0) {
                    width = mMeasuredDimension[0];
                }
            }
        }
        switch (widthMode) {
           //三种测量模式;
            case View.MeasureSpec.EXACTLY: // 相当于match_parent
                width = widthSize;
            case View.MeasureSpec.AT_MOST: // 相当于wrap_content
            case View.MeasureSpec.UNSPECIFIED: //未指明的；未详细说明的
        }
 
        switch (heightMode) {
            case View.MeasureSpec.EXACTLY:
                height = heightSize;
            case View.MeasureSpec.AT_MOST:
            case View.MeasureSpec.UNSPECIFIED:
        }
        setMeasuredDimension(width, height);
    }
 
    private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,
                                   int heightSpec, int[] measuredDimension) {
        try {
            View view = recycler.getViewForPosition(0);
            if (view != null) {
                RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();
 
                int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,
                        getPaddingLeft() + getPaddingRight(), p.width);
 
                int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,
                        getPaddingTop() + getPaddingBottom(), p.height);
 
                view.measure(childWidthSpec, childHeightSpec);
                measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;
                measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;
                recycler.recycleView(view);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
        }
    }
}

为什么你的自定义View wrap_content不起作用？
更多了解：https://www.jianshu.com/p/ca118d704b5e 可以从中找找灵感。
最后感谢wyz上善若水 https://blog.csdn.net/wyz745322878/article/details/52062549