android 自定義View畫圓

package movie.bw.com.myapplication.viewO;

import android.annotation.SuppressLint;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.Shader;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.support.annotation.Nullable;
import android.support.v7.widget.AppCompatImageView;
import android.util.AttributeSet;

public class CircleImageView extends AppCompatImageView {
    private float width;
    private float height;
    private float radius;
    private Paint paint;
    private Matrix matrix;

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

    public CircleImageView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CircleImageView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        paint = new Paint();
        paint.setAntiAlias(true);
        matrix = new Matrix();
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        width = getMeasuredWidth();
        height = getMeasuredHeight();
        radius = Math.min(width, height) / 2;
    }
    @Override
    protected void onDraw(Canvas canvas) {
        Drawable drawable = getDrawable();
        if (drawable == null) {
            super.onDraw(canvas);
            return;
        }
        if (drawable instanceof BitmapDrawable) {
            paint.setShader(initBitmapShader((BitmapDrawable) drawable));
            canvas.drawCircle(width / 2, height / 2, radius, paint);
            return;
        }
        super.onDraw(canvas);
    }
    private BitmapShader initBitmapShader(BitmapDrawable drawable) {
        Bitmap bitmap = drawable.getBitmap();
        BitmapShader bitmapShader = new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        float scale = Math.max(width / bitmap.getWidth(), height / bitmap.getHeight());
        matrix.setScale(scale, scale);
        bitmapShader.setLocalMatrix(matrix);
        return bitmapShader;
    }
}