UIRefreshControl自动启动

Question

是否可以在应用启动时自动启动UIRefreshControl？我试着给self.refreshControl beginRefreshing];打电话，但不起作用。

下面是我的viewDidLoad中的一些代码：

    UIRefreshControl *refreshControl = [[UIRefreshControl alloc] init];
    [refreshControl addTarget:self action:@selector(refreshNowShowingMoviesList:) forControlEvents:UIControlEventValueChanged];
    [self setRefreshControl:refreshControl];
    [refreshControl beginRefreshing];

编辑

下面是我的refreshNowShowingMoviesList方法中的内容：

- (void)refreshNowShowingMoviesList:(id)sender
{
    // Create URL
    NSURL *url = [NSURL URLWithString:kNowShowingMoviesURL"];

    // Initialize URL request
    NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:url];

    // Set value on header
    [urlRequest setValue:kHeaderFieldValue forHTTPHeaderField:kHeaderField];

    // JSON request operation
    AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:urlRequest success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
        NSMutableArray *results = [(NSDictionary *)JSON objectForKey:@"results"];

        if ([results count]) {
            _objects = results;

            // Reload table view
            [self.tableView reloadData];

            // End refreshing
            [(UIRefreshControl *)sender endRefreshing];
        }

    } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
        // End refreshing
        [(UIRefreshControl *)sender endRefreshing];

        // Show error alert
        dispatch_async(dispatch_get_main_queue(), ^{
            UIAlertView *errorAlert = [[UIAlertView alloc] initWithTitle:kSorryTitle message:[error localizedDescription] delegate:self cancelButtonTitle:nil otherButtonTitles:kOk, nil];
            [errorAlert show];
        });
    }];

    // Start operation
    [operation start];
}

并显示错误消息：

'NSInvalidArgumentException', reason: '-[MasterViewController endRefreshing]: unrecognized selector sent to instance 0xa172450'

Answer 1

您应该调用refreshNowShowingMoviesList:nil (请注意nil参数)。这样它就不会崩溃，因为你可以在nil对象上调用任何东西。但看起来你在给refreshNowShowingMoviesList:self打电话。这会导致在MasterViewController上进行endRefreshing调用，但该调用不可用。

或者更简单/更好，在调用之前检查类：

if([sender respondsToSelector:@selector(endRefreshing)]) {
    [(UIRefreshControl *)sender endRefreshing];
}

或者只使用属性而不是发送者参数。史密斯。比如self.tableView.refreshControl..。