<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="CircleImageView">
        <attr name="src" format="reference"/>
    </declare-styleable>
</resources>

class檔案

package com.zdsoft.circleimageview;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.View;

/**
 * Created by Administrator on 2017/1/11.
 */
public class CircleImageView extends View {
    private int src;

    public CircleImageView(Context context) {
        super(context);
    }

    public CircleImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }

    public CircleImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context, attrs);
    }

    /**
     * 接收屬性值
     *
     * @param context
     * @param attrs
     */
    private void init(Context context, AttributeSet attrs) {
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.CircleImageView);
        if (typedArray != null) {
            src = typedArray.getResourceId(R.styleable.CircleImageView_src, R.mipmap.ic_launcher);
            typedArray.recycle();
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        Bitmap sfBitmap = null;//縮放後的bitmap
        //1、獲取Bitmap
        Bitmap bitmap = BitmapFactory.decodeResource(getResources(), src);
        //2、裁剪：對原始bitmap進行處理，看是否需要進行縮放處理，如果bitmap寬度或高度只要不等於圓的直徑。
        if (bitmap.getWidth() != getWidth() || bitmap.getHeight() != getWidth()) {
            sfBitmap = Bitmap.createScaledBitmap(bitmap, getWidth(), getWidth(), false);
        } else {
            sfBitmap = bitmap;
        }
        Bitmap output = Bitmap.createBitmap(sfBitmap.getWidth(), sfBitmap.getHeight(), Bitmap.Config.ARGB_8888);
        //3、例項化新的一張畫布Canvas
        Canvas canvas_new = new Canvas(output);
        //4、對畫布進行裁剪
        Paint paint = new Paint();
        paint.setAntiAlias(true);//抗鋸齒
        paint.setFilterBitmap(true);//抗鋸齒，對點陣圖進行濾波處理
        paint.setDither(true);//設定防抖動，影象比較柔和
        canvas_new.drawCircle(sfBitmap.getWidth() / 2, sfBitmap.getWidth() / 2, sfBitmap.getWidth() / 2, paint);
        //5、核心部分，設定兩張圖片的相交模式，在這裡就是上面繪製的Circle和下面繪製的Bitmap
        Rect rect = new Rect(0, 0, sfBitmap.getWidth(), sfBitmap.getWidth());
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));//取兩層繪製交集,顯示上層
        canvas_new.drawBitmap(sfBitmap, rect, rect, paint);
        //6、把輸出bitmap放到輸出畫布上去
        canvas.drawBitmap(output, 0, 0, null);
    }
}
 

layout檔案

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center">

    <com.zdsoft.circleimageview.CircleImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="15dp"
        app:src="@drawable/a1" />
</RelativeLayout>