http://blog.csdn.net/hursing/article/details/18703599

@Override  
public void onDraw (Canvas canvas) {  
    Rect targetRect = new Rect(50, 50, 1000, 200);  
    Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);  
    paint.setStrokeWidth(3);  
    paint.setTextSize(80);  
    String testString = "测试：ijkJQKA:1234";  
    paint.setColor(Color.CYAN);  
    canvas.drawRect(targetRect, paint);  
    paint.setColor(Color.RED);  
    FontMetricsInt fontMetrics = paint.getFontMetricsInt();  
    int baseline = (targetRect.bottom + targetRect.top - fontMetrics.bottom - fontMetrics.top) / 2;  
    // 下面这行是实现水平居中，drawText对应改为传入targetRect.centerX()  
    paint.setTextAlign(Paint.Align.CENTER);  
    canvas.drawText(testString, targetRect.centerX(), baseline, paint);  
}