Android自定义View实现带4圆角或者2圆角的效果

1 问题

实现任意view经过自定义带4圆角或者2圆角的效果

2 原理

1) 实现view 4圆角

我们只需要把左边的图嵌入到右边里面去，最终显示左边的图就行。

2) 实现view上2圆角

我们只需要把左边的图嵌入到右边里面去，最终显示左边的图就行。

安卓源码里面有这样的类

package android.graphics;
 
/**
 * <p>Specialized implementation of {@link Paint}'s
 * {@link Paint#setXfermode(Xfermode) transfer mode}. Refer to the
 * documentation of the {@link PorterDuff.Mode} enum for more
 * information on the available alpha compositing and blending modes.</p>
 *
 */
public class PorterDuffXfermode extends Xfermode {
 /**
  * Create an xfermode that uses the specified porter-duff mode.
  *
  * @param mode   The porter-duff mode that is applied
  */
 public PorterDuffXfermode(PorterDuff.Mode mode) {
  porterDuffMode = mode.nativeInt;
 }
}

然后我们看下点击mode进去看下

 /**
  * @hide
  */
 public static Mode intToMode(int val) {
  switch (val) {
   default:
   case 0: return Mode.CLEAR;
   case 1: return Mode.SRC;
   case 2: return Mode.DST;
   case 3: return Mode.SRC_OVER;
   case 4: return Mode.DST_OVER;
   case 5: return Mode.SRC_IN;
   case 6: return Mode.DST_IN;
   case 7: return Mode.SRC_OUT;
   case 8: return Mode.DST_OUT;
   case 9: return Mode.SRC_ATOP;
   case 10: return Mode.DST_ATOP;
   case 11: return Mode.XOR;
   case 16: return Mode.DARKEN;
   case 17: return Mode.LIGHTEN;
   case 13: return Mode.MULTIPLY;
   case 14: return Mode.SCREEN;
   case 12: return Mode.ADD;
   case 15: return Mode.OVERLAY;
  }
 }

什么意思呢？

应该可以看得懂，这里每个图片显示的效果是最终的效果，然后很明显，我们这里需要的是SrcIn效果，我们要把左图的效果嵌套到右图里面去。

3 代码实现

1）MyTextView.java文件如下

package com.onemt.sdk.circle;
 
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.RectF;
import android.util.AttributeSet;
 
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.widget.AppCompatTextView;
 
public class MyTextView extends AppCompatTextView {
 
 private final RectF roundRect = new RectF();
 private final Paint desPaint = new Paint();
 private final Paint srcPaint = new Paint();
 private float mRadius = 10;
 private boolean isChange = false;
 
 public MyTextView(@NonNull Context context) {
  super(context);
  init();
 }
 
 public MyTextView(@NonNull Context context, @Nullable AttributeSet attrs) {
  super(context, attrs);
  init();
 }
 
 public MyTextView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  init();
 }
 
 public void change(boolean isChange) {
  this.isChange = isChange;
  invalidate();
 }
 public void init() {
  desPaint.setAntiAlias(true);//设置抗锯齿
  desPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
  srcPaint.setAntiAlias(true);
  float density = getResources().getDisplayMetrics().density;
  mRadius *= density;
 }
 @Override
 protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
  super.onLayout(changed, left, top, right, bottom);
  int width = getWidth();
  int height = getHeight();
  roundRect.set(0, 0, width, height);
 }
 
 @Override
 public void draw(Canvas canvas) {
  //保存最原始的roundRect
  canvas.saveLayer(roundRect, srcPaint, Canvas.ALL_SAVE_FLAG);
  if (isChange) {
   //保存去掉头部2圆角的roundRect(实际就是保留底部的2个圆角)
   canvas.drawRect(roundRect.left, (roundRect.top + roundRect.bottom) / 2, roundRect.right, roundRect.bottom, srcPaint);
   //保存去掉底部2圆角的roundRect(实际就是保留顶部的2个圆角)
//   canvas.drawRect(roundRect.left, roundRect.top, roundRect.right, roundRect.bottom / 2, srcPaint);
  }
  //保存掉头部2圆角的roundRect
  canvas.drawRoundRect(roundRect, mRadius, mRadius, srcPaint);
  //保存叠加后的内容
  canvas.saveLayer(roundRect, desPaint, Canvas.ALL_SAVE_FLAG);
  super.draw(canvas);
  //清空所有的图像矩阵修改状态
  canvas.restore();
 }
 
}

如果你看不懂这个函数drawRoundRect，请看下我的这篇博客介绍 Android之Canvas的drawRoundRect()

2）MainActivity.java文件如下

package com.onemt.sdk.circle;
 
import androidx.appcompat.app.AppCompatActivity;
 
import android.os.Bundle;
import android.view.View;
 
public class MainActivity extends AppCompatActivity {
 
 
 public MyTextView myTextView;
 public boolean isChange = true;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  myTextView = findViewById(R.id.my_textview);
  myTextView.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
    if (isChange) {
     myTextView.change(true);
     isChange = false;
    } else {
     myTextView.change(false);
     isChange = true;
    }
   }
  });
 }
}

3）activity_main.xml文件如下

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:app="http://schemas.android.com/apk/res-auto"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context=".MainActivity">
 
 <com.onemt.sdk.circle.MyTextView
  android:id="@+id/my_textview"
  android:layout_width="100dp"
  android:layout_height="100dp"
  android:background="@color/colorAccent"
  app:layout_constraintBottom_toBottomOf="parent"
  app:layout_constraintLeft_toLeftOf="parent"
  app:layout_constraintRight_toRightOf="parent"
  app:layout_constraintTop_toTopOf="parent" />
 
</androidx.constraintlayout.widget.ConstraintLayout>

4 效果

初始进来如下效果，4圆角效果

然后我们点击图片切换效果如下，上2圆角效果