The calendar app has a costom view, here is another code snippet
@Override
protected void onDraw(Canvas canvas) {
if (mRedrawRequired) {
// if canvas is null, we get the canvas prepared for drawing,
and
// the background bitmap is needed because we do not need the
draw
// the view every time(such as the parent calls scrollTo()
method,
// etc.), only draw it when needed. when onDraw method is called
// again, by default if has nothing done, the view will be
cleared.
// Here we keep the background bitmap saved, we just show the
bitmap
// instead of draw the canvas.
if (null == mCanvas) {
Log.i(TAG, "prepareCanvas.");
prepareCanvas(mVisibleWidth, mVisibleHeight);
}
// else means we can not just show the background bitmap, which
is
// not enough, we should clear the bitmap and redraw it.
// This statement clear will clear the canvas
mCanvas.drawColor(0, PorterDuff.Mode.CLEAR);
drawContent();
mRedrawRequired = false;
}
if (null != *mContentBitmap*) {
canvas.drawBitmap(mContentBitmap, mBitmapRect, mBitmapRect,
mPaint);
}
}
take attention the mContentBitmap here, this is the cache of the canvas, if
it is unnessarry to redraw your whole view, just call canvas.drawBitmap()
method
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Regards
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