/** * Saves the current matrix and clip onto a private stack. Subsequent * calls to translate,scale,rotate,skew,concat or clipRect,clipPath * will all operate as usual, but when the balancing call to restore() * is made, those calls will be forgotten, and the settings that existed * before the save() will be reinstated. * * @return The value to pass to restoreToCount() to balance this save() */ public native int save(); /** * This call balances a previous call to save(), and is used to remove all * modifications to the matrix/clip state since the last save call. It is * an error to call restore() more times than save() was called. */ public native void restore(); /** * Returns the number of matrix/clip states on the Canvas' private stack. * This will equal # save() calls - # restore() calls. */ public native int getSaveCount(); /** * Efficient way to pop any calls to save() that happened after the save * count reached saveCount. It is an error for saveCount to be less than 1. * * Example: * int count = canvas.save(); * ... // more calls potentially to save() * canvas.restoreToCount(count); * // now the canvas is back in the same state it was before the initial * // call to save(). * * @param saveCount The save level to restore to. */ public native void restoreToCount(int saveCount);
做了一个简单实验:
@Override protected void onDraw(Canvas canvas) { // TODO Auto-generated method stub Log.e("FYF", "begin onDraw canvas SaveCount " + canvas.getSaveCount()); super.onDraw(canvas); canvas.save(); Drawable d = getResources().getDrawable(R.drawable.bender03pb); int savecount1 = canvas.save(); canvas.translate(100, 100); canvas.scale(1.5f, 1.5f); int savecount2 = canvas.save(); canvas.rotate(90); canvas.skew(0.5f, 0.5f); Log.e("FYF", savecount1 + " " + savecount2 + " canvas save count: " + canvas.getSaveCount()); d.setBounds(0,0,200,200); d.draw(canvas); canvas.restoreToCount(savecount2); Log.e("FYF", "after restore savecount2, canvas save count: " + canvas.getSaveCount()); d.draw(canvas); canvas.restoreToCount(savecount1); d.draw(canvas); Log.e("FYF", "after restore savecount1, canvas save count: " + canvas.getSaveCount()); canvas.restore(); Log.e("FYF", "end onDraw canvas SaveCount " + canvas.getSaveCount()); } }结果:
E/FYF (31669): begin onDraw canvas SaveCount 1
E/FYF (31669): 2 3 canvas save count: 4
E/FYF (31669): after restore savecount2, canvas save count: 3
E/FYF (31669): after restore savecount1, canvas save count: 2
E/FYF (31669): end onDraw canvas SaveCount 1
后来试着先canvas.restoreToCount(savecount1), 再 canvas.restoreToCount(savecount2), 没有出错,不过canvas.restoreToCount(savecount2)没有生效,
因为savecount2代表的状态在savecount1restore的时候就已经被清除了.
E/FYF (32303): HELLO WORLD!
E/FYF (32303): find tag B2 true
E/FYF (32303): begin onDraw canvas SaveCount 1
E/FYF (32303): 2 3 canvas save count: 4
E/FYF (32303): after restore savecount2, canvas save count: 2
E/FYF (32303): after restore savecount1, canvas save count: 2
E/FYF (32303): end onDraw canvas SaveCount 1
以前都没有注意过canvas 的save()还有返回值,偶然看到restoreToCount()才知道还可以这么用。方便使用。
看样子canvas 在进入onDraw前还被save了一次.