Question

在我的应用程序中，我将图像保存为相册作为资源。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]];

问题是返回的图片是 nil 。我在ALAssetRepresentation引用中读到，当图像不适合时，返回nil。

我将此图片放入具有iPad屏幕大小的UIImageView。我想知道你是否可以帮我解决这个问题？

提前谢谢你。

Answer 1

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仍然被压缩，这意味着它将在第一次被绘制之前被解压缩，因此在主线程上将阻止你的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, 0, (__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
    });
});

ALAsset上的defaultRepresentation fullScreenImage不会返回全屏图像

1 个答案: