Android自定义Drawable之在Drawable中部指定透明区域方法示例

public void draw(@NonNull Canvas canvas) {
 //将绘制操作保存到新的图层，因为图像合成是很昂贵的操作，将用到硬件加速，这里将图像合成的处理放到离屏缓存中进行
 int saveCount = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), srcPaint, Canvas.ALL_SAVE_FLAG);

 //dst 绘制目标图层
 innerDrawable.draw(canvas);

 //设置混合模式
 srcPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
 //src 绘制源图
 canvas.drawPath(srcPath, srcPaint);
 //清除混合模式
 srcPaint.setXfermode(null);
 //还原画布
 canvas.restoreToCount(saveCount);
}

setLayerType(View.LAYER_TYPE_SOFTWARE, null);

import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

/**
 * 说明：支持中间出现透明区域的drawable 

 * 通过{@link #setSrcPath(Path)}设定透明区域的形状 

 * 作者：杨健
 * 时间：2017/9/4.
 */

public class HoleDrawable extends Drawable {
 private Paint srcPaint;
 private Path srcPath = new Path();

 private Drawable innerDrawable;


 public HoleDrawable(Drawable innerDrawable) {
  this.innerDrawable = innerDrawable;
  srcPath.addRect(100, 100, 200, 200, Path.Direction.CW);
  srcPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
  srcPaint.setColor(0xffffffff);
 }

 /**
  * 设置内部透明的部分
  *
  * @param srcPath
  */
 public void setSrcPath(Path srcPath) {
  this.srcPath = srcPath;
 }

 @Override
 public void draw(@NonNull Canvas canvas) {
  innerDrawable.setBounds(getBounds());
  if (srcPath == null || srcPath.isEmpty()) {
   innerDrawable.draw(canvas);
  } else {
   //将绘制操作保存到新的图层，因为图像合成是很昂贵的操作，将用到硬件加速，这里将图像合成的处理放到离屏缓存中进行
   int saveCount = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), srcPaint, Canvas.ALL_SAVE_FLAG);

   //dst 绘制目标图
   innerDrawable.draw(canvas);

   //设置混合模式
   srcPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
   //src 绘制源图
   canvas.drawPath(srcPath, srcPaint);
   //清除混合模式
   srcPaint.setXfermode(null);
   //还原画布
   canvas.restoreToCount(saveCount);
  }
 }

 @Override
 public void setAlpha(int alpha) {
  innerDrawable.setAlpha(alpha);
 }

 @Override
 public void setColorFilter(@Nullable ColorFilter colorFilter) {
  innerDrawable.setColorFilter(colorFilter);
 }

 @Override
 public int getOpacity() {
  return innerDrawable.getOpacity();
 }
}

import android.content.Context;
import android.graphics.Path;
import android.graphics.drawable.HoleDrawable;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.View;
import android.widget.FrameLayout;

/**
 * 能够局部透明的layout，也就是将background处理成带洞洞的效果 

 * 当然了，形状要你自己指定，目前想不到好的思路自动处理各种形状，有的话就直接完善了 

 * 根据个crop_image_cover_view_hole子View的位置，确定透明区域 

 * 作者：杨健
 * 时间：2017/9/4.
 */
public class HoleBackgroundLayout extends FrameLayout {

 private HoleDrawable background;

 public HoleBackgroundLayout(@NonNull Context context) {
  super(context);
  initView(context, null, 0);
 }

 public HoleBackgroundLayout(@NonNull Context context, @Nullable AttributeSet attrs) {
  super(context, attrs);
  initView(context, attrs, 0);
 }

 public HoleBackgroundLayout(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  initView(context, attrs, defStyleAttr);
 }

 private void initView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
  background = new HoleDrawable(getBackground());
  setBackground(background);
 }

 @Override
 protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
  super.onLayout(changed, left, top, right, bottom);
  resetBackgroundHoleArea();
 }

 private void resetBackgroundHoleArea() {
  Path path = null;
  // 以crop_image_cover_view_hole子View为范围构造需要透明显示的区域
  View v0 = findViewById(R.id.crop_image_cover_view_hole);
  if (v0 != null) {
   path = new Path();
   // 矩形透明区域
   path.addRect(v0.getLeft(), v0.getTop(), v0.getRight(), v0.getBottom(), Path.Direction.CW);
  }
  if (path != null) {
   background.setSrcPath(path);
  }
 }
}