一.获取单张图片

思路:

• 1.利用UIImagePickerController可以从系统自带的App(照片\相机)中获得图片
• 2.设置代理,遵守代理协议
• 注意这个UIImagePickerController类比较特殊,需要遵守两个代理协议

@interface ViewController () <UIImagePickerControllerDelegate, UINavigationControllerDelegate>

• 3.实现代理的方法didFinishPickingMediaWithInfo

- (void)getImageFromIpc
{
    // 1.判断相册是否可以打开
    if (![UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypePhotoLibrary]) return;
    // 2. 创建图片选择控制器
    UIImagePickerController *ipc = [[UIImagePickerController alloc] init];
    /**
     typedef NS_ENUM(NSInteger, UIImagePickerControllerSourceType) {
     UIImagePickerControllerSourceTypePhotoLibrary, // 相册
     UIImagePickerControllerSourceTypeCamera, // 用相机拍摄获取
     UIImagePickerControllerSourceTypeSavedPhotosAlbum // 相簿
     }
     */
    // 3. 设置打开照片相册类型(显示所有相簿)  
    ipc.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
    // ipc.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
    // 照相机
    // ipc.sourceType = UIImagePickerControllerSourceTypeCamera;
    // 4.设置代理
    ipc.delegate = self;
    // 5.modal出这个控制器
    [self presentViewController:ipc animated:YES completion:nil];
}

#pragma mark -- <UIImagePickerControllerDelegate>--
// 获取图片后的操作
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info
{
    // 销毁控制器
    [picker dismissViewControllerAnimated:YES completion:nil];

    // 设置图片
    self.imageView.image = info[UIImagePickerControllerOriginalImage];
}

二.获取多张图片

思路:

• 导入头文件#import <Photos/Photos.h>
• PHAsset : 一个资源, 比如一张图片\一段视频
• PHAssetCollection : 一个相簿
• PHImageManager 图片管理者,是单例,发送请求才能从asset获取图片
• PHImageRequestOptions图片请求选项
• 注意:这个类是iOS8开始推广,iOS9开始废弃之前的方法
  系统适配iOS8之前,用下面这个库里面的API

#import <AssetsLibrary/AssetsLibrary.h>

1.获得所有相簿的原图

- (void)getOriginalImages
{
    // 获得所有的自定义相簿
    PHFetchResult<PHAssetCollection *> *assetCollections = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
    // 遍历所有的自定义相簿
    for (PHAssetCollection *assetCollection in assetCollections) {
        [self enumerateAssetsInAssetCollection:assetCollection original:YES];
    }
    
    // 获得相机胶卷
    PHAssetCollection *cameraRoll = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeSmartAlbumUserLibrary options:nil].lastObject;
    // 遍历相机胶卷,获取大图
    [self enumerateAssetsInAssetCollection:cameraRoll original:YES];
}

2.获得所有相簿中的缩略图

- (void)getThumbnailImages
{
    // 获得所有的自定义相簿
    PHFetchResult<PHAssetCollection *> *assetCollections = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
    // 遍历所有的自定义相簿
    for (PHAssetCollection *assetCollection in assetCollections) {
        [self enumerateAssetsInAssetCollection:assetCollection original:NO];
    }
    // 获得相机胶卷
    PHAssetCollection *cameraRoll = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeSmartAlbumUserLibrary options:nil].lastObject;
    [self enumerateAssetsInAssetCollection:cameraRoll original:NO];
}

3.遍历相册

/**
 *  遍历相簿中的所有图片
 *  @param assetCollection 相簿
 *  @param original        是否要原图
 */
- (void)enumerateAssetsInAssetCollection:(PHAssetCollection *)assetCollection original:(BOOL)original
{
    NSLog(@"相簿名:%@", assetCollection.localizedTitle);
    
    PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
    // 同步获得图片, 只会返回1张图片
    options.synchronous = YES;

    // 获得某个相簿中的所有PHAsset对象
    PHFetchResult<PHAsset *> *assets = [PHAsset fetchAssetsInAssetCollection:assetCollection options:nil];
    for (PHAsset *asset in assets) {
        // 是否要原图
        CGSize size = original ? CGSizeMake(asset.pixelWidth, asset.pixelHeight) : CGSizeZero;
        
        // 从asset中获得图片
        [[PHImageManager defaultManager] requestImageForAsset:asset targetSize:size contentMode:PHImageContentModeDefault options:options resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
            NSLog(@"%@", result);
        }];
    }
}