Android开发 在有指定数量item后固定RecyclerView高度

前言

　　下面提供了2种方式，看情况选择使用。

代码部分

方式一

可靠且简单暴力的方式，需要让RecyclerView先setAdapter();

        mRecyclerview.post(new Runnable() { //将修改高度的代码放到RecyclerView最后面执行，让RecyclerView先测量完毕
            @Override
            public void run() {
                if (mRecyclerview.getAdapter() == null || mRecyclerview.getAdapter().getItemCount() <= 4){ //小于4个不固定高度
                    return;
                }
                View view = mRecyclerview.getChildAt(0);
                if (view == null){
                    return;
                }
                int height = view.getHeight() * 4;
                ConstraintLayout.LayoutParams layoutParams = (ConstraintLayout.LayoutParams) mRecyclerview.getLayoutParams();
                layoutParams.height = height;
                mRecyclerview.setLayoutParams(layoutParams);
            }
        });

 

方式二

可能会被父类的布局测量影响

使用时，请注意2点情况：

1. 不要将RecyclerView的android:layout_height属性设置为wrap_content，不然是不会成功的.
2. item的根布局也需要固定高度，不要使用wrap_content,否则下面测算高度时会出现不准确的情况.

    /**
     * 自适应列表View在到指定数量item后固定高度,
     *
     * @param targetNum
     */
    private void adaptiveRecyclerViewHeight(int targetNum) {
        mFamilyListRecyclerview.setLayoutManager(new LinearLayoutManager(getContext()) {
            @Override
            public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec) {
                int count = state.getItemCount();
                if (count > 0) {
                    if (count > targetNum) {
                        count = targetNum;
                    }
                    int realHeight = 0;
                    int realWidth = 0;
                    for (int i = 0; i < count; i++) {
                        View view = recycler.getViewForPosition(0);
                        if (view != null) {
                            measureChild(view, widthSpec, heightSpec);
                            int measuredWidth = View.MeasureSpec.getSize(widthSpec);
                            int measuredHeight = view.getMeasuredHeight();
                            realWidth = realWidth > measuredWidth ? realWidth : measuredWidth;
                            realHeight = realHeight + measuredHeight;
                        }
                    }
                    setMeasuredDimension(realWidth, realHeight);
                } else {
                    super.onMeasure(recycler, state, widthSpec, heightSpec);
                }
            }
        });
    }

End