Android中Bitmap,byte[],Drawable相互转换

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);
 }