不使用UIImagePickerController实现读取相册图片的方法

转载自：http://blog.ilovedev.com/blog/2013/11/03/bu-shi-yong-uiimagepickercontrollershi-xian-du-qu-xiang-ce-tu-pian-de-fang-fa/

在读取系统相册的图片时，一般的实现是使用UIImagePickerController控件，然后实现UIImagePickerControllerDelegate里面的两个回调方法。 本文介绍一种不使用此控件，用ALAssetsLibrary类库枚举出相册下面的图片信息。

旧的常规实现代码如下：

- (void)button2Pressed:(id)sender
{
UIImagePickerController* vc = [[UIImagePickerController alloc] init];
vc.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
vc.delegate = self;
[self presentViewController:vc animated:YES completion:nil];
[vc release];
}

#pragma mark - UIImagePickerControllerDelegate
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
// 图片在这里
UIImage* image = [info objectForKey:UIImagePickerControllerOriginalImage];
[self dismissViewControllerAnimated:YES completion:nil];
}

- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker
{
[self dismissViewControllerAnimated:YES completion:nil];
}

使用新的方法，首先做以下两点： 1.引入头文件：#import (尖括号)AssetsLibrary/AssetsLibrary.h(尖括号) 2.在工程中引入库：AssetsLibrary.framework 具体代码如下：

// 打印信息，仅做演示
- (void)printALAssetInfo:(ALAsset*)asset
{
//取图片的url
NSString *photoURL=[NSString stringWithFormat:@"%@",asset.defaultRepresentation.url];
NSLog(@"photoURL:%@", photoURL);
// 取图片
UIImage* photo = [UIImage imageWithCGImage:asset.defaultRepresentation.fullScreenImage];
NSLog(@"PHOTO:%@", photo);
NSLog(@"photoSize:%@", NSStringFromCGSize(photo.size));
// 取图片缩图图
UIImage* photoThumbnail = [UIImage imageWithCGImage:asset.thumbnail];
NSLog(@"PHOTO2:%@", photoThumbnail);
NSLog(@"photoSize2:%@", NSStringFromCGSize(photoThumbnail.size));
}

-(void)loadImageFromPhotoLibrary
{
// 为了防止界面卡住，可以异步执行
dispatch_async(dispatch_get_main_queue(), ^{
// 获取相册每个组里的具体照片
ALAssetsGroupEnumerationResultsBlock groupEnumerAtion = ^(ALAsset *result, NSUInteger index, BOOL *stop){
if (result!=nil) {
// 检查是否是照片，还可能是视频或其它的
// 所以这里我们还能类举出枚举视频的方法。。。
if ([[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto]) {
[self printALAssetInfo:result];
}
}
};
//获取相册的组
ALAssetsLibraryGroupsEnumerationResultsBlock groupsEnumeration = ^(ALAssetsGroup* group, BOOL* stop){
if (group!=nil) {
NSString *groupInfo=[NSString stringWithFormat:@"%@",group];
NSLog(@"GROUP INFO:%@",groupInfo);

[group enumerateAssetsUsingBlock:groupEnumerAtion];
}
};

ALAssetsLibraryAccessFailureBlock failureblock = ^(NSError *error){
// 相册访问失败的回调，可以打印一下失败原因
NSLog(@"相册访问失败，ERROR:%@", [error localizedDescription]);
};

ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];
[library enumerateGroupsWithTypes:ALAssetsGroupAll
usingBlock:groupsEnumeration
failureBlock:failureblock];
[library release];
});

}

// 同上面的原理，我们再做一个根据URL取图片及缩略图的方法
- (void)loadImageForURL:(NSURL*)photoUrl
{
ALAssetsLibrary *assetLibrary=[[ALAssetsLibrary alloc] init];
[assetLibrary assetForURL:photoUrl
resultBlock:^(ALAsset *asset)
{
[self printALAssetInfo:asset];
}
failureBlock:^(NSError *error)
{
NSLog(@"error=%@",error);
}];
}