先来说一下FontMetrics这个类。这个类是关于字符属性和測量的类

用图能够更精确的知道各个属性的含义：

我们在Layout中有一个ImageView,我们能够通过：

		ImageView item_image = (ImageView)findViewById(R.id.item_image);		item_image.setImageBitmap(makeMessageCenterIcon());

这样的方式来把bitmap来填入ImageView

以下做一个这样的效果的。特别适合有消息通知的icon:

代码能够这样来写:

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是终于须要的画字的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;			}