android - Android 无法在画布上绘制透明矩形

Question

尝试使用透明背景绘制并在其上绘制线条。然而，它绘制了一个黑色矩形而不是 transparet。如果我将颜色更改为红色，它可以正常工作。所以我猜这是透明的问题。

       drawPoints[currentpoint*4+0] = 0; 
       drawPoints[currentpoint*4+1] = 10;
       drawPoints[currentpoint*4+2] = 20; 
       drawPoints[currentpoint*4+3] = 40;

        Canvas mCanvas = sfh.lockCanvas(new Rect(10,20,50,100));
        mCanvas.drawColor(Color.TRANSPARENT);           
        mCanvas.drawLines(drawPoints,mPaint);
        sfh.unlockCanvasAndPost(mCanvas);

为什么会画黑色？

Answer 1

如果你想要透明度，你可以尝试：

mPaint.setAlpha(100);

或 0 到 255 之间的某个值。

希望有帮助。

Answer 2

I find this on the internet, I think that can works

Paint pincel1=new Paint();
paint.setARGB(255,255,0,0);

canvas.drawRect(10,10,ancho-10,40,pincel1);

pincel1.setStyle(Style.STROKE);
canvas.drawRect(10,60,ancho-10,90,pincel1);

pincel1.setStrokeWidth(3);
canvas.drawRect(10,110,ancho-10,140,pincel1);

image http://www.javaya.com.ar/androidya/imagentema/foto137.jpg

thx javaya.com/ar for the code

code

Answer 3

您想将 Paint 对象的颜色设置为 Color.TRANSPARENT，而不是画布的颜色。所以试试

mPaint.setColor(Color.TRANSPARENT);