Android中Drawable和Bitmap互相转化

1. 相关概念

• 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即可。
• Canvas画布，绘图的目的区域。
• Bitmap位图，用于图形的处理。
• Matrix矩阵，进行图形变换。

2. Bitmap相关的转化

2.1. 从资源中获取Bitmap

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

2.2. Bitmap 转为 byte[]

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

2.3. byte[] 转为 Bitmap

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

2.4. 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;  
}

2.6. 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;  
}

2.7. 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;
}

3. Drawable相关的转化

3.1. 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。

3.2. 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);
}