Android中Bitmap,byte[],Drawable相互转化

一、相关概念

1、Drawable就是一个可画的对象，其可能是一张位图（BitmapDrawable），也可能是一个图形（ShapeDrawable），还有可能是一个图层（LayerDrawable），我们根据画图的需求，创建相应的可画对象

2、Canvas画布，绘图的目的区域，用于绘图

3、Bitmap位图，用于图的处理

4、Matrix矩阵

二、Bitmap

1、从资源中获取Bitmap

		Resources res = getResources();
		Bitmap bmp = BitmapFactory.decodeResource(res, R.drawable.icon);

2、Bitmap → byte[]

	public byte[] Bitmap2Bytes(Bitmap bm) {
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		bm.compress(Bitmap.CompressFormat.PNG, 100, baos);
		return baos.toByteArray();
	}

3、byte[] → Bitmap

	public Bitmap Bytes2Bimap(byte[] b) {
		if (b.length != 0) {
			return BitmapFactory.decodeByteArray(b, 0, b.length);
		} else {
			return null;
		}
	}

4、Bitmap缩放

	public static Bitmap zoomBitmap(Bitmap bitmap, int width, int height) {
		int w = bitmap.getWidth();
		int h = bitmap.getHeight();
		Matrix matrix = new Matrix();
		float scaleWidth = ((float) width / w);
		float scaleHeight = ((float) height / h);
		matrix.postScale(scaleWidth, scaleHeight);
		Bitmap newbmp = Bitmap.createBitmap(bitmap, 0, 0, w, h, matrix, true);
		return newbmp;
	}

 5、将Drawable转化为Bitmap

public static Bitmap drawableToBitmap(Drawable drawable) {
		// 取 drawable 的长宽
		int w = drawable.getIntrinsicWidth();
		int h = drawable.getIntrinsicHeight();

		// 取 drawable 的颜色格式
		Bitmap.Config config = drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
				: Bitmap.Config.RGB_565;
		// 建立对应 bitmap
		Bitmap bitmap = Bitmap.createBitmap(w, h, config);
		// 建立对应 bitmap 的画布
		Canvas canvas = new Canvas(bitmap);
		drawable.setBounds(0, 0, w, h);
		// 把 drawable 内容画到画布中
		drawable.draw(canvas);
		return bitmap;
	}

6、获得圆角图片 

	public static Bitmap getRoundedCornerBitmap(Bitmap bitmap, float roundPx) {
		int w = bitmap.getWidth();
		int h = bitmap.getHeight();
		Bitmap output = Bitmap.createBitmap(w, h, Config.ARGB_8888);
		Canvas canvas = new Canvas(output);
		final int color = 0xff424242;
		final Paint paint = new Paint();
		final Rect rect = new Rect(0, 0, w, h);
		final RectF rectF = new RectF(rect);
		paint.setAntiAlias(true);
		canvas.drawARGB(0, 0, 0, 0);
		paint.setColor(color);
		canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
		paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
		canvas.drawBitmap(bitmap, rect, rect, paint);

		return output;
	}

7、获得带倒影的图片

	public static Bitmap createReflectionImageWithOrigin(Bitmap bitmap) {
		final int reflectionGap = 4;
		int w = bitmap.getWidth();
		int h = bitmap.getHeight();

		Matrix matrix = new Matrix();
		matrix.preScale(1, -1);

		Bitmap reflectionImage = Bitmap.createBitmap(bitmap, 0, h / 2, w,
				h / 2, matrix, false);

		Bitmap bitmapWithReflection = Bitmap.createBitmap(w, (h + h / 2),
				Config.ARGB_8888);

		Canvas canvas = new Canvas(bitmapWithReflection);
		canvas.drawBitmap(bitmap, 0, 0, null);
		Paint deafalutPaint = new Paint();
		canvas.drawRect(0, h, w, h + reflectionGap, deafalutPaint);

		canvas.drawBitmap(reflectionImage, 0, h + reflectionGap, null);

		Paint paint = new Paint();
		LinearGradient shader = new LinearGradient(0, bitmap.getHeight(), 0,
				bitmapWithReflection.getHeight() + reflectionGap, 0x70ffffff,
				0x00ffffff, TileMode.CLAMP);
		paint.setShader(shader);
		// Set the Transfer mode to be porter duff and destination in
		paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
		// Draw a rectangle using the paint with our linear gradient
		canvas.drawRect(0, h, w, bitmapWithReflection.getHeight()
				+ reflectionGap, paint);

		return bitmapWithReflection;
	}

 三、Drawable

1、Bitmap转换成Drawable

Bitmap bm=xxx; //xxx根据你的情况获取
BitmapDrawable bd= new BitmapDrawable(getResource(), bm); 
因为BtimapDrawable是Drawable的子类，最终直接使用bd对象即可。

2、Drawable缩放

	public static Drawable zoomDrawable(Drawable drawable, int w, int h) {
		int width = drawable.getIntrinsicWidth();
		int height = drawable.getIntrinsicHeight();
		// drawable转换成bitmap
		Bitmap oldbmp = drawableToBitmap(drawable);
		// 创建操作图片用的Matrix对象
		Matrix matrix = new Matrix();
		// 计算缩放比例
		float sx = ((float) w / width);
		float sy = ((float) h / height);
		// 设置缩放比例
		matrix.postScale(sx, sy);
		// 建立新的bitmap，其内容是对原bitmap的缩放后的图
		Bitmap newbmp = Bitmap.createBitmap(oldbmp, 0, 0, width, height,
				matrix, true);
		return new BitmapDrawable(newbmp);
	}

转自http://dyh7077063.iteye.com/blog/970672