先来说一下FontMetrics这个类，这个类是关于字符属性和测量的类

用图可以更精确的知道各个属性的含义：

我们在Layout中有一个ImageView,我们可以通过：

<span style="white-space:pre">		</span>ImageView item_image = (ImageView)findViewById(R.id.item_image);
		item_image.setImageBitmap(makeMessageCenterIcon());

下面做一个这种效果的，特别适合有消息通知的icon:

代码可以这样来写:

protected Bitmap makeMessageCenterIcon(){
		int mMsgCnt = 4;
		Bitmap icon = BitmapFactory.decodeResource(getResources(), R.drawable.desktop_messageicon);
		if(icon == null){
			return icon;
		}
		
		//make notice icon
		if(mMsgCnt > 0) {
			Bitmap noticeIcon = BitmapFactory.decodeResource(getResources(), R.drawable.notice_count_bg);
			if(noticeIcon != null){
				int h = noticeIcon.getHeight();
				int w = noticeIcon.getWidth();
				
				
				Bitmap noticeIconBmp = Bitmap.createBitmap(w, h, Config.ARGB_8888);//noticeIconBmp是最终需要的画字的bitmap
				Canvas noticeCanvas = new Canvas(noticeIconBmp);
				Paint noticeCntpaint = new Paint();
				noticeCntpaint.setAntiAlias(true);
				noticeCanvas.drawBitmap(noticeIcon, 0, 0, noticeCntpaint);
				noticeCntpaint.setTextAlign(Align.CENTER);
				noticeCntpaint.setColor(getResources().getColor(R.drawable.white));
				
				FontMetrics fontMetrics = noticeCntpaint.getFontMetrics(); 
				float x = noticeIcon.getWidth() / 2;
				float y = (noticeIcon.getHeight() - fontMetrics.ascent) / 2 - 2;  //fontMetrics是在baseline以上的字符最高处的位置
				noticeCanvas.drawText(String.valueOf(mMsgCnt), x, y, noticeCntpaint);  //在canvas上的(x,y)的位置上写mMsgCnt
				
				//draw notice icon onto message icon
				h = icon.getHeight();
				w = icon.getWidth();
				Bitmap iconBmp = Bitmap.createBitmap(w, h, Config.ARGB_8888);
				Canvas canvas = new Canvas(iconBmp);
				
				Paint paint = new Paint();
				paint.setAntiAlias(true);
				canvas.drawBitmap(icon, 0, 0, paint);
				float left = icon.getWidth() - noticeIcon.getWidth();
				float top = 0;
				canvas.drawBitmap(noticeIconBmp, left, top, paint);
				
				return iconBmp;
			}
		}
		return icon;
		
	}

android在如果绘制自定义的bitmap,然后返回给ImageView