覆盖的OnDraw怎么改图纸时（安卓） [英] Override onDraw to change how the drawing occurs (Android)

问题描述

我如何可以覆盖的OnDraw 让我把什么话都被画（作为位图），并把它？

下面作品的方法，但它不幸的是，这种方法包括创建一个位图的整个屏幕的尺寸 - 不只是被吸引到该区域。如果我用这个来绘制UI元素，它被重新绘制的每个UI元素的。这可以更有效地完成？

  @覆盖
保护无效的OnDraw（帆布油画）{
    // TODO：减少从多个图纸的负担
    点阵位图= Bitmap.createBitmap（canvas.getWidth（），canvas.getHeight（），Config.ARGB_8888）;
    帆布屏幕外=新的Canvas（位）;
    super.onDraw（屏幕外）;
    //然后画在屏幕上
    涂料P =新的油漆（）;
    p.setXfermode（新PorterDuffXfermode（PorterDuff.Mode.DARKEN））;
    canvas.drawBitmap（位图，0，0，p）的;
}
 

解决方案

以下code将更加高效。

 公共类MyView的扩展TextView的{
    私人帆布屏幕外;

    公共MyView的（上下文的背景下，ATTRS的AttributeSet，诠释defStyle）{
        超（背景下，ATTRS，defStyle）;
    }

    公共MyView的（上下文的背景下，ATTRS的AttributeSet）{
        超（背景下，ATTRS）;
    }

    公共MyView的（上下文的背景下）{
        超（上下文）;
    }

    @覆盖
    保护无效的OnDraw（帆布油画）{
        //我们希望超直接绘制到屏幕外的画布，使我们没有得到一个无限深的递归调用
        如果（帆布==屏幕外）{
            super.onDraw（屏幕外）;
        }
        其他{
            //我们的外图像使用该视图的尺寸，而不是在画布
            点阵位图= Bitmap.createBitmap（的getWidth（），getHeight（）都会，Config.ARGB_8888）;
            屏幕外=新的Canvas（位）;
            super.draw（屏幕外）;
            //创建涂料绘制效果
            涂料P =新的油漆（）;
            p.setXfermode（新PorterDuffXfermode（PorterDuff.Mode.DARKEN））;
            //绘制在画布上。幸运的是，这一类使用相对坐标，这样我们就不必担心在那里这种观点是实际定位。
            canvas.drawBitmap（位图，0，0，p）的;
        }
    }
}
 

How can I override onDraw so that I take what would have been drawn (as a bitmap) and transform it?

The method below works, but it unfortunately, this method involves creating a bitmap the size of the entire screen - not just the area that is drawn to. If I use this to draw UI elements, it is redrawn for each UI element. Can this be done more efficiently?

@Override
protected void onDraw(Canvas canvas) {
    //TODO: Reduce the burden from multiple drawing
    Bitmap bitmap=Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Config.ARGB_8888);
    Canvas offscreen=new Canvas(bitmap);
    super.onDraw(offscreen);
    //Then draw onscreen
    Paint p=new Paint();
    p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DARKEN));
    canvas.drawBitmap(bitmap, 0, 0, p);
}

解决方案

The following code will be much more efficient.

public class MyView extends TextView{
    private Canvas offscreen;

    public MyView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

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

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

    @Override
    protected void onDraw(Canvas canvas) {
        //We want the superclass to draw directly to the offscreen canvas so that we don't get an infinitely deep recursive call
        if(canvas==offscreen){
            super.onDraw(offscreen);
        }
        else{
            //Our offscreen image uses the dimensions of the view rather than the canvas
            Bitmap bitmap=Bitmap.createBitmap(getWidth(), getHeight(), Config.ARGB_8888);
            offscreen=new Canvas(bitmap);
            super.draw(offscreen);
            //Create paint to draw effect
            Paint p=new Paint();
            p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DARKEN));
            //Draw on the canvas. Fortunately, this class uses relative coordinates so that we don't have to worry about where this View is actually positioned.
            canvas.drawBitmap(bitmap, 0, 0, p);
        }
    }
}

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