Android中Bitmap回收问题

Question

使用Bitmap的静态方法createScaledBitmap来创建一个符合规格的Bitmap的时候，原生的bitmap是否需要回收？

代码如下：

private void initDragBitmap() {
    Bitmap srcBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.mingren);
    mDragBitmap = Bitmap.createScaledBitmap(srcBitmap, FLOAT_BALL_WIDTH, FLOAT_BALL_HEIGHT, true);
    srcBitmap.recycle();
}

代码中srcBitmap是否需要回收？

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补充问题：

看了大家的回复，基本可以确定如果srcBitmap后续不再使用了，确实是可以手动recycle的，同时它本身也是个局部变量，是可以等待系统GC的。

那新问题来了（或者说我最初想问的问题来了），当createScaledBitmap方法中传入的宽和高跟srcBitmap相同时，通过createScaledBitmap代码注释可以看出它是将srcBitmap返回了，这个时候我强行recycle了srcBitmap，会不会导致mDragBitmap也为null？

源码注释：

    /**
     * Creates a new bitmap, scaled from an existing bitmap, when possible. If the
     * specified width and height are the same as the current width and height of
     * the source bitmap, the source bitmap is returned and no new bitmap is
     * created.
     *
     * @param src       The source bitmap.
     * @param dstWidth  The new bitmap's desired width.
     * @param dstHeight The new bitmap's desired height.
     * @param filter    true if the source should be filtered.
     * @return The new scaled bitmap or the source bitmap if no scaling is required.
     * @throws IllegalArgumentException if width is <= 0, or height is <= 0
     */
    public static Bitmap createScaledBitmap(Bitmap src, int dstWidth, int dstHeight,
            boolean filter) {
            }

Answer 1

你可以等待GC去回收，当然，像你这样手动回收是个好习惯。

补答：

会的，如果两个引用都是同一个对象，那么你使用recycle时会让对象中的图片被清理。不过清理的是对象中的图片数据，并不是对象本身，所以说mDragBitmap不会为null，但是使用mDragBitmap中的图片数据时会报错。

你这里可以进行进行一次判断再回收：

if (srcBitmap != mDragBitmap) {  // 内存地址不同，说明不是同一个对象
    srcBitmap.recycle();
}

Answer 2

如果你确信没有进一步的操作就可以调用其recycler方法，释放内存；如果后续有getPixels()与setPixels()的调用就不要随意释放内存，等待GC的回收，否则会抛异常。

Answer 3

private void initDragBitmap() {

Bitmap srcBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.mingren);
mDragBitmap = Bitmap.createScaledBitmap(srcBitmap, FLOAT_BALL_WIDTH, FLOAT_BALL_HEIGHT, true);
srcBitmap.recycle();

}

就题主以上代码，和大家探讨个问题，是不是用srcBitmap=null；可以尽快让gc回收呢？

Answer 4

/*Free the native object associated with this bitmap, and clear the
 * reference to the pixel data. This will not free the pixel data synchronously;
 * it simply allows it to be garbage collected if there are no other references.
 * The bitmap is marked as "dead", meaning it will throw an exception if
 * getPixels() or setPixels() is called, and will draw nothing. This operation
 * cannot be reversed, so it should only be called if you are sure there are no
 * further uses for the bitmap. This is an advanced call, and normally need
 * not be called, since the normal GC process will free up this memory when
 * there are no more references to this bitmap.
 */
public void recycle() {
    if (!mRecycled && mFinalizer.mNativeBitmap != 0) {
        if (nativeRecycle(mFinalizer.mNativeBitmap)) {
            // return value indicates whether native pixel object was actually recycled.
            // false indicates that it is still in use at the native level and these
            // objects should not be collected now. They will be collected later when the
            // Bitmap itself is collected.
            mBuffer = null; 
            mNinePatchChunk = null;
        }
        mRecycled = true;
    }
}
回复3楼,@xialong
可以看到,源码也是将数据制为`null`,一般情况下,你可以`bitmap.recycle()`与`bitmap=null`一起用;

题主确定不需要用到那个`bitmap`就可以手动回收,`recycle()`的回收是`不可逆`的

Answer 5

带现在的主流版本上，Google已经将Bitmap的内存放到堆中去了，这个回收也交给了gc，所以楼主不用考虑这个这个问题了。内存不够时就自动回收了。