我正在尝试从UIImageView加载并显示照片库（相机胶卷）中的最后一张照片，一切正常！除了一件事！如果库中没有可用的图像，则应用程序崩溃！这是我的代码：
-(void)importLastImage {
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
// Enumerate just the photos and videos group by using ALAssetsGroupSavedPhotos.
[library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
// Within the group enumeration block, filter to enumerate just photos.
[group setAssetsFilter:[ALAssetsFilter allPhotos]];
// Chooses the photo at the last index
[group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:([group numberOfAssets]-1)]
options:0
usingBlock:^(ALAsset *alAsset, NSUInteger index, BOOL *innerStop) {
// The end of the enumeration is signaled by asset == nil.
if (alAsset) {
ALAssetRepresentation *representation = [alAsset defaultRepresentation];
latestPhoto = [UIImage imageWithCGImage:[representation fullResolutionImage]];
_lastImage.image = latestPhoto;
}else {
//no image found !
}
}];
}
failureBlock: ^(NSError *error) {
// Typically you should handle an error more gracefully than this.
NSLog(@"No groups");
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"ERROR" message:@"No Image found" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:nil, nil];
[alert show];
}];
}
最佳答案
我决定在此处发布一个代码片段，您可以将其复制粘贴，其中包含我上面的评论中的建议。
如果我的英语不太清楚（我不是英语为母语的人），请提前抱歉。
您的崩溃是由于该行代码[group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:([group numberOfAssets]-1)]
正如您所说，问题是，当库中没有可用图像时，numberOfAssets返回0，
并且由于您是使用numberOfAssets - 1创建索引的，因此您基本上是在尝试创建一个负索引，这会使程序崩溃。
我只是添加了一个if语句，以检查'if'numberOfAssets（表示它不是0），
只有这样，才执行以下枚举，因此，请避免出现任何负索引的情况。
无论如何，您可以在这里结伴：
-(void)importLastImage {
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
// Enumerate just the photos and videos group by using ALAssetsGroupSavedPhotos.
[library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
// Within the group enumeration block, filter to enumerate just photos.
[group setAssetsFilter:[ALAssetsFilter allPhotos]];
if([group numberOfAssets]) {
// Chooses the photo at the last index
[group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:([group numberOfAssets]-1)]
options:0
usingBlock:^(ALAsset *alAsset, NSUInteger index, BOOL *innerStop) {
// The end of the enumeration is signaled by asset == nil.
if (alAsset) {
ALAssetRepresentation *representation = [alAsset defaultRepresentation];
latestPhoto = [UIImage imageWithCGImage:[representation fullResolutionImage]];
_lastImage.image = latestPhoto;
}else {
//no image found !
}
}];
} else {
NSLog(@"No images in photo library");
}
}
failureBlock: ^(NSError *error) {
// Typically you should handle an error more gracefully than this.
NSLog(@"No groups");
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"ERROR" message:@"No Image found" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:nil, nil];
[alert show];
}];
}