主要思想:
重寫imageview,在imageview上畫一個四個圓角的方框,並把畫布下一一個圓角半徑長度,這樣就能不顯示下面對的四個角

重寫ImageView:

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import
 
 android.graphics.RectF;
import android.util.AttributeSet;
import android.widget.ImageView;

class RoundImageView extends ImageView {

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

    public RoundImageView(Context context) {
        super
 
(context);
        init();
    }

    private final RectF roundRect = new RectF();
    private float rect_adius = 15;
    private final Paint maskPaint = new Paint();
    private final Paint zonePaint = new Paint();

    private void init() {
        maskPaint.setAntiAlias(true);
        maskPaint.setXfermode(new
 
 PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
        zonePaint.setAntiAlias(true);
        zonePaint.setColor(Color.WHITE);
        float density = getResources().getDisplayMetrics().density;
        rect_adius = rect_adius * density;
    }

    public void setRectAdius(float adius) {
        rect_adius = adius;
        invalidate();
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right,
                            int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        int w = getWidth();
        int h = getHeight();
        roundRect.set(0, 0, w, h + rect_adius);//畫布下移半徑長度
    }


    @Override
    public void draw(Canvas canvas) {
        canvas.saveLayer(roundRect, zonePaint, Canvas.ALL_SAVE_FLAG);
        canvas.drawRoundRect(roundRect, rect_adius, rect_adius, zonePaint);
        canvas.saveLayer(roundRect, maskPaint, Canvas.ALL_SAVE_FLAG);
        super.draw(canvas);
        canvas.restore();
    }
}

注:該類可以直接在xml中呼叫,和imageView用法一樣,不過圓角半徑要動態在程式碼中設定,呼叫該物件的setRectAdius(adius)方法