Android异常java.lang.IllegalStateException: Immutable bitmap passed to Canvas constructor

使用BitmapFactory的decodeResource方法需注意，不能直接修改res里面的图片，需要添加copy(Bitmap.Config.ARGB_8888,true)方法，否则会报以下异常：

Caused by: java.lang.IllegalStateException: Immutable bitmap passed to Canvas constructor

代码如下：

    private Bitmap getBitmap(Context context, int resId) {
        BitmapFactory.Options options = new BitmapFactory.Options();
        TypedValue value = new TypedValue();
        context.getResources().openRawResource(resId,value);
        options.inTargetDensity = value.density;
        options.inScaled = false;
        return BitmapFactory.decodeResource(context.getResources(),resId,options).copy(Bitmap.Config.ARGB_8888,true);
    }