自定义 RecyclerView.ItemDecoration

来源：互联网发布：洛枫网络软件公司编辑：程序博客网时间：2024/05/01 04:54

public class MyItemDecoration extends RecyclerView.ItemDecoration{    public MyItemDecoration() {        super();    }    @Override    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {        super.onDraw(c, parent, state);        KJLoger.debug("==================onDraw==================");    }    @Override    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {        super.onDrawOver(c, parent, state);        KJLoger.debug("==================onDrawOver==================");    }    @Override    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {        super.getItemOffsets(outRect, view, parent, state);        KJLoger.debug("==================getItemOffsets==================");    }}

执行，可看见执行顺序，如图：

所以，首先看：

1. getItemOffsets该方法，该方法中，我们主要修改参数outRect，该参数可控制I每个tem项的上、下、左、右间隔（相当于控制Item显示位置）。在之前先给每个Item设置背景颜色，例：

修改前：

public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {    super.getItemOffsets(outRect, view, parent, state);    Log.i("debug", "==================getItemOffsets==================");    }

修改之后：

public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {    super.getItemOffsets(outRect, view, parent, state);    Log.i("debug", "==================getItemOffsets==================");    outRect.set(10,10,10,10);}

2. onDraw：负责Item的绘制，可以在原始Item的基础上进行添加绘制。（此方法中的绘制图案并不会覆盖元有图案，只是相当于透明蒙版（带色玻璃）一样覆盖在上层），该方法可用于：绘制分割线，附带Item蒙版等。

如下代码是添加绘制蓝色蒙版：

@Override    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {        super.onDraw(c, parent, state);        Log.i("debug", "==================onDraw==================");        //计算子元素实际左右坐标        int left = parent.getPaddingLeft()+itemSpace;        int right = parent.getWidth() - parent.getPaddingRight()-itemSpace;        int top = 0;        int bootom = 0;        int count = parent.getChildCount();        for (int i = 0; i < count; i++) {            View child = parent.getChildAt(i);            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();//            top = child.getBottom();            top = child.getTop();            bootom = child.getBottom();            c.drawRect(left,top,right,bootom,paint);        }    }

效果如图：（其他效果可自行尝试）

3. onDrawOver：该方法同样是用于Item的绘制，与onDraw不同的是该方法所绘制的东东会覆盖在onDraw以及之前的基础图案之上，与上面同样的代码：

@Override    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {        super.onDrawOver(c, parent, state);        Log.i("debug", "==================onDrawOver==================");        //计算子元素实际左右坐标        int left = parent.getPaddingLeft()+itemSpace;        int right = parent.getWidth() - parent.getPaddingRight()-itemSpace;        int top = 0;        int bootom = 0;        int count = parent.getChildCount();        for (int i = 0; i < count; i++) {            View child = parent.getChildAt(i);            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();//            top = child.getBottom();            top = child.getTop();            bootom = child.getBottom();            c.drawRect(left,top,right,bootom,paint);        }    }

此时我们再来看看效果：

此时，我们只能看见一片蓝，因为之前的东东被onDrawOver里面的东东给覆盖了。

这就差不多是这三个方法的大致用法了，当然各种用途就要靠大家自我开发了。

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