Android中Drawable和Bitmap的区别及互相转化

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);  
    }