如何在 for 循环（Xcode、Objective C、iOS）中等待回调方法（或）响应？

Question

在我的代码中，我有多个位置，我必须检查所有位置是否正确（使用 google api 检查）如果位置正确，我必须获取该位置的坐标。

我正在尝试在 for 循环中编写代码，有什么方法可以等待 for 循环中的响应。

我在下面粘贴我的代码。

提前致谢。

for (int locationsCount=0;locationsCount<results.count;locationsCount++)
    {
        NSString *googlelocations = [[results objectAtIndex:locationsCount]objectForKey:@"description"];

        if ([locationAddress isEqualToString:googlelocations])
        {
            [[LocationManager share] fetchLatLngForPlacename:googlelocations placeId:[[results objectAtIndex:locationsCount] objectForKey:@"place_id"] completion:^(double lat, double lng, NSError *error)
            {
                [SVProgressHUD dismiss];

                if (error) {

                }else {

                    CLLocation *locationCoordinates = [[CLLocation alloc]initWithLatitude:lat longitude:lng];

                    NSMutableArray *globalArray = [[LocationManager share]getManualInterLocationArray];
                    NSMutableDictionary *dict = [[globalArray objectAtIndex:selectedTextField.tag] mutableCopy];

                    [dict setObject:locationCoordinates forKey:@"location_coordinates"];

                    [dict setObject:googlelocations forKey:@"location_Address"];

                    [dict setObject:[NSNumber numberWithBool:true] forKey:@"manualEntry_Flag"];

                    [globalArray replaceObjectAtIndex:selectedTextField.tag withObject:dict];

                    [[LocationManager share]saveManualInterLocationArray:globalArray];

                }

            }];
        }
    }

Answer 1

我为这个需求使用了递归方法，它现在工作正常。递归方法是满足此要求的最佳且简单的方法。

-(void)addressValidation:(int)locationCount andCompletion:(void(^)(BOOL isSuccess))callBack{
if (manualarraycount >= globalArray.count)
{
    callBack(true);
    return;
}

[[LocationManager share] fetchOfflineAutoCompleteSuggestionForKey:locationAddress LocationCoordinates:location Radius:duration completion:^(NSArray *results, NSError *error){
    // --------- do what you want ------------
    [self addressValidation:manualarraycount+1 andCompletion:callBack];
}];

}

Answer 2

尝试使用递归。创建函数

-(void)setLocation:(NSUInteger)locationCount andCompletion:(void (^))completionBlock{
    if (locationsCount>=results.count) {
       if (completion) {
              completion();
       }
       return;
    }
    NSString *googlelocations = [[results objectAtIndex:locationsCount]objectForKey:@"description"];

    if ([locationAddress isEqualToString:googlelocations])
    {
        [[LocationManager share] fetchLatLngForPlacename:googlelocations placeId:[[results objectAtIndex:locationsCount] objectForKey:@"place_id"] completion:^(double lat, double lng, NSError *error)
        {
            [SVProgressHUD dismiss];

            if (error) {

            }else {

                CLLocation *locationCoordinates = [[CLLocation alloc]initWithLatitude:lat longitude:lng];

                NSMutableArray *globalArray = [[LocationManager share]getManualInterLocationArray];
                NSMutableDictionary *dict = [[globalArray objectAtIndex:selectedTextField.tag] mutableCopy];

                [dict setObject:locationCoordinates forKey:@"location_coordinates"];

                [dict setObject:googlelocations forKey:@"location_Address"];

                [dict setObject:[NSNumber numberWithBool:true] forKey:@"manualEntry_Flag"];

                [globalArray replaceObjectAtIndex:selectedTextField.tag withObject:dict];

                [[LocationManager share]saveManualInterLocationArray:globalArray];

            }

        }];
    }
}

在您的完成块中，使用增量计数调用函数本身：

[self setLocation:locationCount++ andCompletion:nil];

并开始重复调用您需要从 0 开始的函数

[self setLocation:0 andCompletion:^{
 // handle completion
 }];

Answer 3

可以使用调度组，就像下面的伪代码：

dispatch_group_t loadDetailsGroup=dispatch_group_create();

for(id thing in thingsToDo)
{
    dispatch_group_enter(loadDetailsGroup);

    // call method with completion callback, and in the callback run
    dispatch_group_leave(loadDetailsGroup);
}

// Now outside the loop wait until everything is done. NOTE: this will block!
dispatch_group_wait(loadDetailsGroup, DISPATCH_TIME_FOREVER);

如果您在主线程上运行它，则不应阻止它，以便 UI 保持响应。所以你可以在后台做等待部分，然后在完成后可能在主线程中做一些事情：

// to background 
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),^{
    // wait in background
    dispatch_group_wait(loadDetailsGroup, DISPATCH_TIME_FOREVER);

    // back to main (not needed if what you need to do may happen in background)
    dispatch_async(dispatch_get_main_queue(),^{

        // do stuff here that affects the UI
    });
});

编辑： 正如 Kurt Revis 指出的，如果您想异步等待并进行回调，dispatch_group_notify() 更适合。所以上面的整个代码可以压缩成：

dispatch_group_t loadDetailsGroup=dispatch_group_create();

for(id thing in thingsToDo)
{
    dispatch_group_enter(loadDetailsGroup);

    // call method with completion callback, and in the callback run
    dispatch_group_leave(loadDetailsGroup);
}

// Now outside the loop wait until everything is done. NOTE: this will
// not block execution, the provided block will be called
// asynchronously at a later point.
dispatch_group_notify(loadDetailsGroup,dispatch_get_main_queue(),^{

    // Callback
});