Bitmap.java中createBitmap函數調用的是以下重構方法
public static Bitmap createBitmap(Bitmap source, int x, int y, int width, int height,
Matrix m, boolean filter) {
checkXYSign(x, y);
checkWidthHeight(width, height);
if (x + width > source.getWidth()) {
throw new IllegalArgumentException("x + width must be <= bitmap.width()");
}
if (y + height > source.getHeight()) {
throw new IllegalArgumentException("y + height must be <= bitmap.height()");
}
// check if we can just return our argument unchanged
if (!source.isMutable() && x == 0 && y == 0 && width == source.getWidth() &&
height == source.getHeight() && (m == null || m.isIdentity())) {
return source;
}
int neww = width;
int newh = height;
Canvas canvas = new Canvas();
Bitmap bitmap;
Paint paint;
Rect srcR = new Rect(x, y, x + width, y + height);
RectF dstR = new RectF(0, 0, width, height);
Config newConfig = Config.ARGB_8888;
final Config config = source.getConfig();
// GIF files generate null configs, assume ARGB_8888
if (config != null) {
switch (config) {
case RGB_565:
newConfig = Config.RGB_565;
break;
case ALPHA_8:
newConfig = Config.ALPHA_8;
break;
//noinspection deprecation
case ARGB_4444:
case ARGB_8888:
default:
newConfig = Config.ARGB_8888;
break;
}
}
if (m == null || m.isIdentity()) {
bitmap = createBitmap(neww, newh, newConfig, source.hasAlpha());
paint = null; // not needed
} else {
final boolean transformed = !m.rectStaysRect();
RectF deviceR = new RectF();
m.mapRect(deviceR, dstR);
neww = Math.round(deviceR.width());
newh = Math.round(deviceR.height());
bitmap = createBitmap(neww, newh, transformed ? Config.ARGB_8888 : newConfig,
transformed || source.hasAlpha());
canvas.translate(-deviceR.left, -deviceR.top);
canvas.concat(m);
paint = new Paint();
paint.setFilterBitmap(filter);
if (transformed) {
paint.setAntiAlias(true);
}
}
// The new bitmap was created from a known bitmap source so assume that
// they use the same density
bitmap.mDensity = source.mDensity;
canvas.setBitmap(bitmap);
canvas.drawBitmap(source, srcR, dstR, paint);
canvas.setBitmap(null);
return bitmap;
}
注意發現其中有以下代碼
// check if we can just return our argument unchanged
if (!source.isMutable() && x == 0 && y == 0 && width == source.getWidth() &&
height == source.getHeight() && (m == null || m.isIdentity())) {
return source;
}
以上代碼的邏輯是:如果源位圖是 immutable且請求傳回的位圖是和源位圖一樣的,則直接傳回源位圖,并不建立新位圖。
是以你在使用它的時候很可能會傳回一個你之前傳進來的bitmap。是以如果你把認為是臨時變量的bitmap回收掉之後,其實是把不該回收的也回收了。這時就會抛出詭異的bitmap回收問題,說是使用了recycled的bitmap。如果一定需要建立一個拷貝的話,可以嘗試使用Bitmap.copy(Config config, boolean isMutable)方法代替。