如何将<应用程序中的图片>保存到<手机相册>中

三大步骤

/*
 1.添加图片到【相机胶卷】
 1> UIImageWriteToSavedPhotosAlbum函数
 2> AssetsLibrary框架
 3> Photos框架(推荐)
 
 2.拥有一个【自定义相册】
 1> AssetsLibrary框架
 2> Photos框架(推荐)
 
 3.将刚才添加到【相机胶卷】的图片，引用（添加）到【自定义相册】
 1> AssetsLibrary框架
 2> Photos框架(推荐)
 */

Photos框架须知

/*
 Photos框架须知
 1.PHAsset : 一个PHAsset对象代表一张图片或者一个视频文件
 1> 负责查询一堆的PHAsset对象
 
 2.PHAssetCollection : 一个PHAssetCollection对象代表一个相册
 1> 负责查询一堆的PHAssetCollection对象
 
 3.PHAssetChangeRequest
 1> 负责执行对PHAsset的【增删改】操作
 2> 这个类只能放在-[PHPhotoLibrary performChanges:completionHandler:] 或者 -[PHPhotoLibrary performChangesAndWait:error:]方法的block中使用
 
 4.PHAssetCollectionChangeRequest
 1> 负责执行对PHAssetCollection的【增删改】操作
 2> 这个类只能放在-[PHPhotoLibrary performChanges:completionHandler:] 或者 -[PHPhotoLibrary performChangesAndWait:error:]方法的block中使用
 */

• 代码实现

//当用户点击"保存图片"的按钮时
-(IBAction )save {
  /*
     requestAuthorization方法的功能
     1.如果用户还没有做过选择，这个方法就会弹框(是否允许该程序访问相册)让用户做出选择
     1> 用户做出选择以后才会回调block
     
     2.如果用户之前已经做过选择，这个方法就不会再弹框，直接回调block，传递现在的授权状态给block
     */

PHAuthorizationStatus oldStatus = [PHPhotoLibrary authorizationStatus];
    
        //此方法在异步线程调用
        NSLog(@"%@",[NSThread currentThread]);
        
        //将和UI相关的东西放在主线程去做
    [PHPhotoLibrary requestAuthorization:^(PHAuthorizationStatus status) {
        dispatch_async(dispatch_get_main_queue(), ^{
            switch (status) {
                case PHAuthorizationStatusAuthorized: {
                    //  保存图片到相册
                    [self saveImageIntoAlbum];
                    break;
                }
                    
                case PHAuthorizationStatusDenied: {
                    if (oldStatus == PHAuthorizationStatusNotDetermined) return;
                    
                    XMGLog(@"提醒用户打开相册的访问开关")
                    break;
                }
                    
                case PHAuthorizationStatusRestricted: {
                    [SVProgressHUD showErrorWithStatus:@"因系统原因，无法访问相册！"];
                    break;
                }
                    
                default:
                    break;
            }
        });
    }];

/**
 *  获得刚才添加到【相机胶卷】中的图片
 */
- (PHFetchResult<PHAsset *> *)createdAssets
{
    __block NSString *createdAssetId = nil;
    
    // 添加图片到【相机胶卷】
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        createdAssetId = [PHAssetChangeRequest creationRequestForAssetFromImage:self.imageView.image].placeholderForCreatedAsset.localIdentifier;
    } error:nil];
    
    if (createdAssetId == nil) return nil;
    
    // 在保存完毕后取出图片
    return [PHAsset fetchAssetsWithLocalIdentifiers:@[createdAssetId] options:nil];
}

/**
 *  获得【自定义相册】
 */
- (PHAssetCollection *)createdCollection
{
    // 获取软件的名字作为相册的标题
    NSString *title = [NSBundle mainBundle].infoDictionary[(NSString *)kCFBundleNameKey];
    
    // 获得所有的自定义相册
    PHFetchResult<PHAssetCollection *> *collections = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
    for (PHAssetCollection *collection in collections) {
        if ([collection.localizedTitle isEqualToString:title]) {
            return collection;
        }
    }
    
    // 代码执行到这里，说明还没有自定义相册
    
    __block NSString *createdCollectionId = nil;
    
    // 创建一个新的相册
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        createdCollectionId = [PHAssetCollectionChangeRequest creationRequestForAssetCollectionWithTitle:title].placeholderForCreatedAssetCollection.localIdentifier;
    } error:nil];
    
    if (createdCollectionId == nil) return nil;
    
    // 创建完毕后再取出相册
    return [PHAssetCollection fetchAssetCollectionsWithLocalIdentifiers:@[createdCollectionId] options:nil].firstObject;
}

/**
 *  保存图片到相册
 */
- (void)saveImageIntoAlbum
{
    // 获得相片
    PHFetchResult<PHAsset *> *createdAssets = self.createdAssets;
    
    // 获得相册
    PHAssetCollection *createdCollection = self.createdCollection;
    
    if (createdAssets == nil || createdCollection == nil) {
        [SVProgressHUD showErrorWithStatus:@"保存失败！"];
        return;
    }
    
    // 将相片添加到相册
    NSError *error = nil;
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        PHAssetCollectionChangeRequest *request = [PHAssetCollectionChangeRequest changeRequestForAssetCollection:createdCollection];
        [request insertAssets:createdAssets atIndexes:[NSIndexSet indexSetWithIndex:0]];
    } error:&error];
    
    // 保存结果
    if (error) {
        [SVProgressHUD showErrorWithStatus:@"保存失败！"];
    } else {
        [SVProgressHUD showSuccessWithStatus:@"保存成功！"];
    }
}

常见的BUG

• BUG 1

This method can only be called from inside of -[PHPhotoLibrary performChanges:completionHandler:] or -[PHPhotoLibrary performChangesAndWait:error:]

• 解决方案1

 // Asynchronously 异步执行操作
 [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
    [PHAssetChangeRequest creationRequestForAssetFromImage:self.imageView.image];
 } completionHandler:^(BOOL success, NSError * _Nullable error) {
    XMGLog(@"保存完毕")
 }];

• 解决方案2

 // Synchronously 同步执行操作
 NSError *error = nil;
 [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
    [PHAssetChangeRequest creationRequestForAssetFromImage:self.imageView.image];
 } error:&error];

• BUG 2

//注意:PHPhotoLibrary的performChangesAndWait的block不能嵌套的,因为这个方法是同步方法,这样会卡主线程造成死锁
 [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
 
    } error:nil];
 } error:nil];

其他注意细节

// 这个方法只适合加载普通的plist文件，不能用来加载Info.plist
[NSDictionary dictionaryWithContentsOfFile:pathForResource:]

CoreFoundation和Foundation之间的数据类型，可以互相转换

只有遵守了NSFastEnumeration协议的对象才能使用for-in循环

• 被readonly修饰的属性

/* 自动生成的内容：number的getter声明+实现、_number成员变量*/
@property (nonatomic, assign, readonly) NSInteger number;