自定义RecyclerView.LayoutManager知识总结

最新推荐文章于 2024-05-05 09:09:08 发布

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本文深入解析了RecyclerView中创建水平布局的实现方式，包括如何通过OrientationHelper获取View的测量宽度、装饰边框大小以及布局边界等关键信息。文章详细介绍了自定义HorizontalHelper的方法，如getStartAfterPadding、getDecoratedMeasurement、getDecoratedMeasurementInOther和getTotalSpace，这些方法对于理解RecyclerView内部工作原理至关重要。

public static OrientationHelper createHorizontalHelper(
            RecyclerView.LayoutManager layoutManager) {
        return new OrientationHelper(layoutManager) {
            
            .....

            @Override
            public int getStartAfterPadding() {
                return mLayoutManager.getPaddingLeft();
            }

            // mLayoutManager.getDecoratedMeasuredWidth(view)
            // 获取的宽度是view的测量宽度+ Decorated(装饰的左右边框)的大小
            // 还得加上view的layout_marginRight 和 layout_marginLeft
            // 这个宽度由内而外  依次是 view的宽度, view的margin边距, 装饰框的偏移宽度 
            @Override
            public int getDecoratedMeasurement(View view) {
                final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)
                        view.getLayoutParams();
                return mLayoutManager.getDecoratedMeasuredWidth(view) + params.leftMargin
                        + params.rightMargin;
            }

            //  这个方法就是mLayoutManager.getDecoratedMeasuredWidth(view)
            // public int getDecoratedMeasuredWidth(View child) {
            //   final Rect insets = ((LayoutParams) 
            // child.getLayoutParams()).mDecorInsets;
            //           view测量宽度                   装饰边框的左侧宽度   装饰边框的右侧宽度 
            //   return child.getMeasuredWidth() + insets.left + insets.right;
            // }


            @Override
            public int getDecoratedMeasurementInOther(View view) {
                final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)
                        view.getLayoutParams();
                return mLayoutManager.getDecoratedMeasuredHeight(view) + params.topMargin
                        + params.bottomMargin;
            }

            @Override
            public int getTotalSpace() {
                return mLayoutManager.getWidth() - mLayoutManager.getPaddingLeft()
                        - mLayoutManager.getPaddingRight();
            }

            .......
        };
    }