在布局中RecyclerView添加android:layout_height="wrap_content"这一属性，发现竟然不起作用，RecyclerView的item加载完成，屏幕下方所有的区域都会被占用，若为一般界面倒是看不出太大的影响，但当Activity为弹窗显示时影响就很大了，如下图效果：

图一.png

我们想要实现的效果如下：

图二.png

我们通过自定义MyGridLayoutManager继承GridLayoutManager来解决这个问题，直接上代码：

import android.content.Context;
import android.graphics.Rect;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.view.ViewGroup;

public class MyGridLayoutManager extends GridLayoutManager {


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

    private int[] measuredSize = new int[2];

    @Override
    public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec) {
        final int widthMode = View.MeasureSpec.getMode(widthSpec);
        final int heightMode = View.MeasureSpec.getMode(heightSpec);
        final int widthSize = View.MeasureSpec.getSize(widthSpec);
        final int heightSize = View.MeasureSpec.getSize(heightSpec);

        int spanWidth = 0;
        int spanHeight = 0;

        int viewWidth = 0;
        int viewHeight = 0;

        int spanCount = getSpanCount();

        for (int i = 0; i < getItemCount(); i++) {

            measureScrapChild(recycler, i, View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED), View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED), measuredSize);

            if (i % spanCount == 0) {
                spanWidth = measuredSize[0];
                spanHeight = measuredSize[1];
            } else {
                if (getOrientation() == VERTICAL) {
                    spanWidth += measuredSize[0];
                    spanHeight = Math.max(spanHeight, measuredSize[1]);
                } else {
                    spanWidth = Math.max(spanWidth, measuredSize[0]);
                    spanHeight += measuredSize[1];
                }
            }

            if (i % spanCount == spanCount - 1 || i == getItemCount() - 1) {
                if (getOrientation() == VERTICAL) {
                    viewWidth = Math.max(viewWidth, spanWidth);
                    viewHeight += spanHeight;
                } else {
                    viewWidth += spanWidth;
                    viewHeight = Math.max(viewHeight, spanHeight);
                }
            }
        }

        int finalWidth;
        int finalHeight;

        switch (widthMode) {
            case View.MeasureSpec.EXACTLY:
                finalWidth = widthSize;
                break;
            case View.MeasureSpec.AT_MOST:
                finalWidth = Math.min(widthSize, viewWidth);
                break;
            case View.MeasureSpec.UNSPECIFIED:
                finalWidth = viewWidth;
                break;
            default:
                finalWidth = widthSize;
                break;
        }

        switch (heightMode) {
            case View.MeasureSpec.EXACTLY:
                finalHeight = heightSize;
                break;
            case View.MeasureSpec.AT_MOST:
                finalHeight = Math.min(heightSize, viewHeight);
                break;
            case View.MeasureSpec.UNSPECIFIED:
                finalHeight = viewHeight;
                break;
            default:
                finalHeight = heightSize;
                break;
        }

        setMeasuredDimension(finalWidth, finalHeight);
    }


    private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec, int heightSpec, int[] measuredDimension) {

        View view = recycler.getViewForPosition(position);

        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;

            Rect decoratorRect = new Rect();
            calculateItemDecorationsForChild(view, decoratorRect);
            measuredDimension[0] += decoratorRect.left;
            measuredDimension[0] += decoratorRect.right;
            measuredDimension[1] += decoratorRect.top;
            measuredDimension[1] += decoratorRect.bottom;

            recycler.recycleView(view);
        }
    }
}

在代码中使用方法

        mrecycler.setLayoutManager(new MyGridLayoutManager(this,3));