Android开发之自定义圆角矩形图片ImageView

android中的ImageView只能显示矩形的图片，这样一来不能满足我们其他的需求，比如要显示圆角矩形的图片，这个时候，我们就需要自定义ImageView了，其原理就是首先获取到图片的Bitmap，然后进行裁剪对应的圆角矩形的bitmap，然后在onDraw（）进行绘制圆角矩形图片输出。

自定义的圆形的ImageView类的实现代码如下：

package com.xc.xcskin.view;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.PorterDuff.Mode;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.widget.ImageView;

/**
 * 自定义的圆角矩形ImageView，可以直接当组件在布局中使用。
 * @author caizhiming
 *
*/
public class XCRoundRectImageView extends ImageView{

private Paint paint;

public XCRoundRectImageView(Context context) {  
this(context,null);  
    }  

public XCRoundRectImageView(Context context, AttributeSet attrs) {  
this(context, attrs,0);  
    }  

public XCRoundRectImageView(Context context, AttributeSet attrs, int defStyle) {  
super(context, attrs, defStyle); 
        paint  = new Paint();
    }  

/**
     * 绘制圆角矩形图片
     * @author caizhiming
*/
    @Override  
protected void onDraw(Canvas canvas) {  

        Drawable drawable = getDrawable();  
if (null != drawable) {  
            Bitmap bitmap = ((BitmapDrawable) drawable).getBitmap();  
            Bitmap b = getRoundBitmap(bitmap, 20);  
final Rect rectSrc = new Rect(0, 0, b.getWidth(), b.getHeight());  
final Rect rectDest = new Rect(0,0,getWidth(),getHeight());
            paint.reset();  
            canvas.drawBitmap(b, rectSrc, rectDest, paint);  

        } else {  
super.onDraw(canvas);  
        }  
    }  

/**
     * 获取圆角矩形图片方法
     * @param bitmap
     * @param roundPx,圆角的弧度
     * @return Bitmap
     * @author caizhiming
*/
private Bitmap getRoundBitmap(Bitmap bitmap, int roundPx) {  
        Bitmap output = Bitmap.createBitmap(bitmap.getWidth(),  
                bitmap.getHeight(), Config.ARGB_8888);  
        Canvas canvas = new Canvas(output);  

final int color = 0xff424242;

final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());  
final RectF rectF = new RectF(rect);
        paint.setAntiAlias(true);  
        canvas.drawARGB(0, 0, 0, 0);  
        paint.setColor(color);  
int x = bitmap.getWidth(); 

        canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
        paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));  
        canvas.drawBitmap(bitmap, rect, rect, paint);  
return output;  


    }  
}  

注：getRoundBitmap(Bitmap bitmap, int roundPx)中第二个参数为图片的圆角弧度

xml布局文件中直接引用即可：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >


    <com.xc.xcskin.view.XCRoundRectImageView
        android:id="@+id/roundRectImageView"  
        android:layout_centerInParent="true" 
        android:layout_width="200dp"   
        android:layout_height="80dp"
        android:src="@drawable/roundimageview"/>



</RelativeLayout>

最后：效果图如下：