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, , baos);
　　return baos.toByteArray();
}

3、byte[] → Bitmap

public Bitmap Bytes2Bimap(byte[] b) {
        if (b.length != ) {
            return BitmapFactory.decodeByteArray(b, , 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, , , 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(, , 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(, , w, h);
        final RectF rectF = new RectF(rect);
        paint.setAntiAlias(true);
        canvas.drawARGB(, , , );
        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 = ;
        int w = bitmap.getWidth();
        int h = bitmap.getHeight();

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

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

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

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

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

        Paint paint = new Paint();
        LinearGradient shader = new LinearGradient(, bitmap.getHeight(), ,
                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(, 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, , , width, height,
                matrix, true);
        return new BitmapDrawable(newbmp);
    }

　　本文转自dyh7077063的博客http://dyh7077063.iteye.com/blog/970672