在彈出框中使用RecyclerView 展示一個列表，其中彈出框的高度要隨著列表數目的高度變化。

這個需求有兩種解決方案：

1.自定義一個LinearLayoutManager ，動態修改RecyclerView 的佈局高度

import android.content.Context;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;

/**
 * Created by lengqi on 2016/3/18.
 */
 

public class AutoHightLinearLayoutManager extends LinearLayoutManager {

    private int size;

    public AutoHightLinearLayoutManager(Context context, int sizeParam) {
        super(context);
        size = sizeParam;
    }

    @Override
    public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int
 
 widthSpec, int heightSpec) {
      '''  int count = state.getItemCount();'''
       '''   if (count > 0) { ''' 
            View view = recycler.getViewForPosition(0);
            if (view != null) {
                measureChild(view, widthSpec, heightSpec);
                int measuredWidth = View.MeasureSpec.getSize(widthSpec);
                int
 
 measuredHeight = view.getMeasuredHeight();
                setMeasuredDimension(measuredWidth, measuredHeight * size);
            }
       '''   } else { ''' 
            '''  super.onMeasure(recycler, state, widthSpec, heightSpec); ''' 
         ''' } ''' 
    }
}

注意高亮程式碼，要判定這個itemCount，不然 recycler.getViewForPosition(0)就會報IndexOutOfBoundsException錯誤。

2. 使用StaggeredGridLayoutManager

new StaggeredGridLayoutManager(modeList.size(), StaggeredGridLayoutManager.HORIZONTAL)

int spanCount, int orientation

注意使用寫法的順序。在setAdapter之後。

  RecyclerView mModeView = (RecyclerView) window.findViewById(R.id.rv_speed_modes);

        modeAdapter = new ModeAdapter(modeList);
        mModeView.setAdapter(modeAdapter);
        modeAdapter.notifyDataSetChanged();
        mModeView.setLayoutManager(new StaggeredGridLayoutManager(modeList.size(), StaggeredGridLayoutManager.HORIZONTAL));
        mModeView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL_LIST));