android在如果绘制自定义的bitmap,然后返回给ImageView

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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());

这种方式来把bitmap来填入ImageView

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 iconif(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bitmapCanvas 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 iconh = 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;}

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