getTextBounds 方法作用

		 Rect mBounds = new Rect();

		mPaint.setColor(Color.BLUE);
		canvas.drawRect(0, 0, getWidth(), getHeight(), mPaint);
		mPaint.setColor(Color.YELLOW);
		mPaint.setTextSize(30);
		String text = String.valueOf(mCount);
		mPaint.getTextBounds(text, 0, text.length(), mBounds);
		float textWidth = mBounds.width();
		float textHeight = mBounds.height();
		canvas.drawText(text, getWidth() / 2 - textWidth / 2, getHeight() / 2
				+ textHeight / 2, mPaint);

 		getTextBounds 是将TextView 的文本放入一个矩形中， 测量TextView的高度和宽度，还有一下方法

		参考：http://blog.csdn.net/it_transformers/article/details/46041899