RecyclerView——ItemDecoration笔记

来源：互联网发布：smali文件转java 编辑：程序博客网时间：2024/06/05 22:52

之前项目中看到了系统工程中有的模块RecyclerView里面的Item分割线，竟然使用的是一个View，于是我随手改了一下，在这里顺便复习一下相关的知识。

首先呢需要继承RecyclerView.ItemDecoration然后重写下面的方法

Public Methods void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) 获取项的偏移量（指定outRect指定中的 top、left、right、bottom 就可以控制各个方向的间隔） void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) 绘制组件的UI效果（所有decoration都在item绘制之前绘制，在 ItemView 内容之下绘制图形） void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) decoration在view之后绘制（在 ItemView 内容之上绘制图形）

下面我主要去讨论onDraw中去画普通的分割线
1. LinearLayoutManager中设置分割线（VERTICAL）

@Override    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {        super.getItemOffsets(outRect, view, parent, state);        outRect.bottom = 10;    }    @Override    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {        int childCount = parent.getChildCount();        int left = parent.getPaddingLeft();        int right = parent.getWidth() - parent.getPaddingRight();        for (int i = 0; i < childCount; i++) {            View childAt = parent.getChildAt(i);            float top = childAt.getBottom();            float bottom = childAt.getBottom() + 10;            Shader shader = new LinearGradient(                    left, right, bottom, bottom, Color.parseColor("#FFBBFF"),                    Color.parseColor("#EBEBEB"), Shader.TileMode.MIRROR);            mPaint.setShader(shader);            c.drawRect(left, top, right, bottom, mPaint);        }    }

实现的效果如下：

这里写图片描述

LinearLayoutManager中设置分割线（HORIZONTAL）

@Override    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {        super.getItemOffsets(outRect, view, parent, state);        outRect.right = 10;    }    @Override    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {        int childCount = parent.getChildCount();        for (int i = 0; i < childCount; i++) {            View childAt = parent.getChildAt(i);            int left = childAt.getRight();            int right = childAt.getRight() + 10;            float top = childAt.getTop();            int bottom = childAt.getHeight() - childAt.getTop();            c.drawRect(left, top, right, bottom, mPaint);        }    }

效果如下：

这里写图片描述
3.用户在设置了GridLayoutManager的情况下设置分割线：

@Override    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {        super.getItemOffsets(outRect, view, parent, state);        int position = parent.getChildAdapterPosition(view);        if (isLastColumn(position, parent)) {            right = 0;        }        if (isLastRow(parent)) {            bottom = 0;        }        outRect.set(0, 0, right, bottom);    } /*判断是不是最后一行*/    private boolean isLastRow(RecyclerView parent) {        GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager();        int spanCount = layoutManager.getSpanCount();        int itemCount = parent.getAdapter().getItemCount();        int lastRawCount = itemCount % spanCount;        if (lastRawCount == 0 || lastRawCount < spanCount) {            return true;        }        return false;    /*判断是不是最后一列*/    private boolean isLastColumn(int position, RecyclerView parent) {        GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager();        int spanCount = layoutManager.getSpanCount();        //如果是最后一列的话，那么余数为0        if ((position + 1) % spanCount == 0) {            return true;        }        return false;    }

因为我们在给网格划线的时候，不想画出屏幕边缘左右两条线，所以进行了判断。
接着我们就要重写onDraw方法，画网格需要画两条线，也很简单，直接看代码

    @Override    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {        drawHorizontal(c, parent);        drawVertical(c, parent);    }    private void drawVertical(Canvas c, RecyclerView parent) {        int count = parent.getChildCount();        for (int i = 0; i < count; i++) {            View childView = parent.getChildAt(i);            //这样左边就不会也画线了，如果需要左侧划线那么设置childView.getLeft();            int left = childView.getRight();            int right = left + 10;            int top = childView.getTop();            int bottom = childView.getBottom() + 10;            c.drawRect(left, top, right, bottom, mPaint);        }    }    private void drawHorizontal(Canvas c, RecyclerView parent) {        int count = parent.getChildCount();        for (int i = 0; i < count; i++) {            View childView = parent.getChildAt(i);            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) childView.getLayoutParams();            int left = childView.getLeft() - params.leftMargin;            int right = childView.getRight() + params.rightMargin;            int top = childView.getBottom() + params.bottomMargin;            int bottom = top + 10;            c.drawRect(left, top, right, bottom, mPaint);        }    }

效果图如下：

这里写图片描述

Google官方也提供了设置分割线的方法：
recyclerView.addItemDecoration(new DividerItemDecoration(this,DividerItemDecoration.VERTICAL));

上面很多的篇幅，都用来介绍了onDraw的方法，后面还有一个方法是onDrawOver，这个方法也很神奇。因为在这个
方法中通过Canvas可以直接把一些图片或者其他数据直接绘制在Item上，所以这个方法可以实现一些商品的排行榜什么的。
具体的使用方法，以及实现的炫酷效果可以在网上搜索。

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