android中canvas.drawText参数的介绍以及绘制一个文本居中的案例

float baseline = height/2 + mPaint.getTextSize()/2 - mPaint.getFontMetrics().descent;文字尺寸就是

protected void onDraw(Canvas canvas) {  
    String testString = "测试：gafaeh:1234";  
    Paint mPaint = new Paint();  
    mPaint.setStrokeWidth(3);  
    mPaint.setTextSize(40);  
    mPaint.setColor(Color.RED);  
    mPaint.setTextAlign(Align.LEFT);  
    Rect bounds = new Rect();  
    mPaint.getTextBounds(testString, 0, testString.length(), bounds);  
    FontMetricsInt fontMetrics = mPaint.getFontMetricsInt();  
    int baseline = (getMeasuredHeight() + mPaint.getTextSize) / 2 - fontMetrics.descent;  
    canvas.drawText(testString,getMeasuredWidth() / 2 - bounds.width() / 2, baseline, mPaint);  
}