翻译画布和偏移操作栏

Question

Please bear with me if this isn't clear, this is my first posting here.

I'm drawing a couple of lines on a canvas and trying to translate the canvas to centre the lines on the screen. The trouble is, I have an actionbar (using actionbarsherlock) which I want to exclude from the translation ie I want the top of the view to be under the action bar.

As it is, the data is centred vertically on the whole screen height, but I want it to be centred vertically only on the visible part of the canvas under the action bar.

Any ideas of the best way to achieve this?

@Override
protected void onDraw(Canvas canvas) {
    Paint paint = mPaint;

    paint.setAntiAlias(true);
    paint.setColor(Color.WHITE);
    paint.setStyle(Paint.Style.FILL);


    int centrew = canvas.getWidth()/2;
    int centreh = canvas.getHeight()/2;

    canvas.translate(centrew, centreh);
    canvas.drawLine(0, -5, 0, 5, mPaint);
    canvas.drawLine(5, 0, -5, 0, mPaint);

}

Answer 1

if you know the exact size of the bar, you could apply it it to the overall canvas height to increase the shift:

int maxV = canvas.getHeight() + barHeight;
int centreh = maxV/2;

I am assuming, the bar is on top, covering apart of the canvas, so the shift (from the top left corner) has to be greater. If the bar is on the bottom, the shift should be reduced:

int maxV = canvas.getHeight() - barHeight;
int centreh = maxV/2;

EDIT: If the bar has a different size in pixels on different devices, you have to hack a bit to make it work. You can safely make assuptions about the bar and revise them in case they don't hold. You could assume a certain ratio reserved for the bar and adapt the absolute pixel count accordingly (the oneliner is rather for illustration):

int maxV = Math.round(canvas.getHeight()*(1f + barRatio)); 

You can further adapt the ratio depending on the aspect ratio of the screen to make it work even better.

Unfortunately there is no really clean solution as you cannot read the current layout and extract sizes.

Answer 2

The solution I used was as described here :

http://developer.android.com/resources/samples/HoneycombGallery/src/com/example/android/hcgallery/TitlesFragment.html

Basically my activity has the following layout listener defined:

ViewTreeObserver.OnGlobalLayoutListener layoutListener = new ViewTreeObserver.OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
        mmv.setAbShift(MunroBag.this.actionBar.getHeight());
    }
};  

Then the view class has the following method defined:

    public void setAbShift(int shift)
    {
        abShift = shift;
        this.invalidate();
    }

So onDraw gets called and the shift is applied to the view depending on the actionBar height.