Question

所以我有一个表视图，在didSelectRowAtIndexPath方法中，我想根据选择的行推送视图控制器。但是，要确定要推送哪个视图，我需要执行Parse（我使用parse.com后端为我的应用程序）后台提取，并且我想在此查询的完成处理程序中执行推送。但问题是，如果我多次点击按钮，那么在完成后会将多个视图推送到我的导航堆栈，并使用以下代码：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
// call super because we're a custom subclass.
[super tableView:tableView didSelectRowAtIndexPath:indexPath];
UserDetailsViewController *controller = [[DetailsViewController alloc] initWithNibName:nil
                                                                                    bundle:nil];
UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];

PFQuery *query = [PFQuery queryWithClassName:self.parseClassName];
[query includeKey:@"key1"];
[query whereKey:@"key2" containsString:((UILabel *)(cell.contentView.subviews[1])).text];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error){
    Model *model = [[Model alloc] initWithPFObject:[objects objectAtIndex:0]];
    controller.annotation = model;
    [self.navigationController pushViewController:controller animated:YES];
}];
[tableView deselectRowAtIndexPath:indexPath animated:YES];
}

如何锁定完成块以仅执行一次推送，因为即使用户在推送发生之前依次点击多个行，也可以说是第一次点击的indexPath。

Answer 1

尝试类似：

[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error){
    if (self.navigationController.topViewController == self) {
        Model *model = [[Model alloc] initWithPFObject:[objects objectAtIndex:0]];
        controller.annotation = model;
        [self.navigationController pushViewController:controller animated:YES];
    }
}];

这样，如果您已在self之上安装了另一个视图控制器，它就不会推送。并且还要确保你在主线程上做了所有这些。

Answer 2

有很多方法可以做到其中一个是

取一个实例BOOL isRowSelectedToViewPush; // set isRowSelectedToViewPush = NO;在viewWillAppear方法

中

和

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    // call super because we're a custom subclass.
    if(!isRowSelectedToViewPush ) {
    isRowSelectedToViewPush = YES;
    [super tableView:tableView didSelectRowAtIndexPath:indexPath];
    UserDetailsViewController *controller = [[DetailsViewController alloc] initWithNibName:nil
                                                                                        bundle:nil];
    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];

    PFQuery *query = [PFQuery queryWithClassName:self.parseClassName];
    [query includeKey:@"key1"];
    [query whereKey:@"key2" containsString:((UILabel *)(cell.contentView.subviews[1])).text];
    [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error){
        Model *model = [[Model alloc] initWithPFObject:[objects objectAtIndex:0]];
        controller.annotation = model;
        [self.navigationController pushViewController:controller animated:YES];
    [tableView deselectRowAtIndexPath:indexPath animated:YES];

    }];

    }
 }

如何从完成块安全地推送视图控制器？

2 个答案: