在我的应用程序中,我将图像保存为专辑作为资产.我也想检索它们并全屏显示它们.我使用以下代码：
ALAsset *lastPicture = [scrollArray objectAtIndex:iAsset];
ALAssetRepresentation *defaultRep = [lastPicture defaultRepresentation];
UIImage *image = [UIImage imageWithCGImage:[defaultRep fullScreenImage]
scale:[defaultRep scale] orientation:
(UIImageOrientation)[defaultRep orientation]];
问题是返回的图像是零.我在ALAssetRepresentation参考中读到,当图像不适合时,返回nil.
我把这个图像放到了一个大小与iPad屏幕相同的UIImageView上.我想知道你是否可以帮我解决这个问题？
先感谢您.
解决方法
我不是fullScreenImage或fullResolutionImage的粉丝.我发现当你对队列中的多个资产执行此操作时,即使你立即释放UIImage,内存使用量也会大幅增加而不应该增加.此外,当使用fullScreenImage或fullResolutionImage时,返回的UIImage仍然是压缩的,这意味着它将在第一次绘制之前被解压缩,因此在主线程上将阻止您的UI.
我更喜欢使用这种方法.
-(UIImage *)fullSizeImageForAssetRepresentation:(ALAssetRepresentation *)assetRepresentation
{
UIImage *result = nil;
NSData *data = nil;
uint8_t *buffer = (uint8_t *)malloc(sizeof(uint8_t)*[assetRepresentation size]);
if (buffer != NULL) {
NSError *error = nil;
NSUInteger bytesRead = [assetRepresentation getBytes:buffer fromOffset:0 length:[assetRepresentation size] error:&error];
data = [NSData dataWithBytes:buffer length:bytesRead];
free(buffer);
}
if ([data length])
{
CGImageSourceRef sourceRef = CGImageSourceCreateWithData((__bridge CFDataRef)data,nil);
NSMutableDictionary *options = [NSMutableDictionary dictionary];
[options setObject:(id)kcfBooleanTrue forKey:(id)kCGImageSourceShouldAllowFloat];
[options setObject:(id)kcfBooleanTrue forKey:(id)kCGImageSourceCreateThumbnailFromImageAlways];
[options setObject:(id)[NSNumber numberWithFloat:640.0f] forKey:(id)kCGImageSourceThumbnailMaxPixelSize];
//[options setObject:(id)kcfBooleanTrue forKey:(id)kCGImageSourceCreateThumbnailWithTransform];
CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(sourceRef,(__bridge CFDictionaryRef)options);
if (imageRef) {
result = [UIImage imageWithCGImage:imageRef scale:[assetRepresentation scale] orientation:(UIImageOrientation)[assetRepresentation orientation]];
CGImageRelease(imageRef);
}
if (sourceRef)
CFRelease(sourceRef);
}
return result;
}
你可以像这样使用它：
// Get the full image in a background thread
dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_HIGH,0),^{
UIImage* image = [self fullSizeImageForAssetRepresentation:asset.defaultRepresentation];
dispatch_async(dispatch_get_main_queue(),^{
// Do something with the UIImage
});
});
