ios - 在 For 循环结束时显示 UIAlertView...如果没有错误

Question

我的以下代码循环遍历 Parse.com 的数组，以从本地数据存储上传到服务器。当然，这里的问题是，它为每个成功的条目创建一个 UIAlertView...这很快就会变得烦人。我怎样才能改变它，以便它仍然只在没有错误的情况下显示，但只在循环结束时执行一次？

-(void)uploadToParse {

    int i;
    for (i = 0; i < [self.objects count]; i++) {
        PFObject *entry = [self.objects objectAtIndex:i];


    NSString *imageFileName = [entry[@"FamilyName"] stringByAppendingString:@".png"];
    NSLog(@"%@", imageFileName);
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *filePath = [[paths objectAtIndex:0] stringByAppendingPathComponent:imageFileName];
    UIImage *newImage = [UIImage imageWithContentsOfFile:filePath];
    NSData* data = UIImagePNGRepresentation(newImage);


    PFFile *imageFile = [PFFile fileWithName:@"Locationimage.png" data:data];

    [entry setObject:imageFile forKey:@"HousePicture"];


    [entry saveInBackgroundWithBlock:^(BOOL succeeded, NSError * _Nullable error) {
        if (!error) {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Upload Complete" message:@"Successfully added your Bible Distribution data." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
            [alert show];


            [entry unpinInBackgroundWithName:@"Share" block:^(BOOL succeeded, NSError * _Nullable error) {

            }];

        }
    }];


    [entry unpinInBackgroundWithName:@"Share" block:^(BOOL succeeded, NSError * _Nullable error) {
        [self loadObjects];
    }];

    }
}

Answer 1

我建议使用 dispatch_group。它们允许您对任务进行排队，并且只有在每个任务完成后才会调用完成处理程序。

这应该有效:

-(void)uploadToParse {

    dispatch_group_t uploadGroup = dispatch_group_create();
    int i;
    for (i = 0; i < [self.objects count]; i++) {

        dispatch_group_enter(uploadGroup);
        // ... Your code that sets up the upload task


       [entry saveInBackgroundWithBlock:^(BOOL succeeded, NSError * _Nullable error) {
           dispatch_group_leave(uploadGroup);
        }];
    }

    dispatch_group_notify(uploadGroup, dispatch_get_main_queue(),^{
        // This gets called after each task completes.
        // Add code to show alert view here.
    });
}