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: 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

总结

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