Question

如何创建多个视图可以访问的数据源？

我当前的项目有TabBarController链接到多个视图，所有视图都需要访问同一个好友列表。

目前，我将数据源存储在名为DataHolder的单例类中，代码显示在下面。

DataHolder.m

#import "DataHolder.h"
@interface DataHolder(){
    DataQuery *dataQuery;
    NSMutableArray *friendList;
}
@end
@implementation DataHolder
+(DataHolder*)sharedInstance{
    static DataHolder *_sharedInstance = nil;
    static dispatch_once_t oncePredicate;
    dispatch_once(&oncePredicate, ^{
        _sharedInstance = [[DataHolder alloc]init];
    });
    return _sharedInstance;
}

-(id)init{
    self = [super init];
    if (self){
        NSLog(@"DataHolder init method called");
             dataQuery =[[DataQuery alloc]init];

    }
    return self;
}

-(NSMutableArray *)getFriendList{
    NSLog(@"Friend List from DataHolder %@", [dataQuery getFriendList]);
    return [dataQuery getFriendList];
}

-(void)logout{
    [friendList removeAllObjects];
}

@end

我遇到的问题是我一次不能拥有多个视图来保存数据。我目前在每个viewController中使用NSMutableArray属性并让它们调用self.Array = [NSMutableArray ArrayWithArray:[DataHolder SharedInstance]GetFriendList]];这并不总是返回任何数据，特别是如果之前调用了另一个viewController。我也觉得令人费解的是，一些viewControllers将不显示数据，而另一个拥有数据，下次我运行应用程序时，它会有一个具有数据的不同viewController。

编辑：这是执行查询的dataQuery类，DataHolder保留在其中。

DataQuery.m

@interface DataQuery(){

    NSMutableArray *friendsToAccept;
    //NSMutableArray *friendsList;
    int *count;
}

@end
@implementation DataQuery

-(id)init{
    self = [super init];
    if (self){
        self.friendsList = [NSMutableArray new];
        //[self.friendsList mutableArrayValueForKey:@"friendsArray"];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(getFriendList) name:@"friendList" object:nil];
        self.currentUser = [[CurrentUser sharedInstance]getCurrentUser];

        [self friendListQueryWithDataSource:self.friendsList];
        //[self checkForFriends];

    }
    return self;
}
-(NSMutableArray *)getFriendList{
    return self.friendsList;
}

-(void)friendListQueryWithDataSource:(NSMutableArray*)datasource{
    PFRelation *friendRelation = [self.currentUser relationForKey:@"friendRelation"];
    PFQuery *acceptedQuery = [friendRelation query];
    acceptedQuery.cachePolicy = kPFCachePolicyCacheThenNetwork;


        [acceptedQuery findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
            if (error){
                NSLog(@"ERROR: %@ %@", error, [error userInfo]);
            }else{
                self.friendsList = [NSMutableArray arrayWithArray:objects];
                NSLog(@"Friend List from DataQuery %@", self.friendsList);
            }
        }];


}

以下是视图控制器如何设置以显示数据

#import "ConnectionTableViewController.h"


@interface ConnectionTableViewController (){
    DataHolder  *dataHolder;
}

@end

@implementation ConnectionTableViewController

- (void)viewDidLoad
{
    self.pending = [NSArray new];
    NSLog(@"%@", self.pending);
    self.friendList = [NSMutableArray new];
    self.edgesForExtendedLayout = UIRectEdgeNone;
    backgroundQueue = dispatch_queue_create("word", NULL);
    self.friendList = [NSMutableArray arrayWithArray:[[DataHolder sharedInstance] getFriendList]];


      [super viewDidLoad];
}

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"friendList"]) {
        for (PFUser *user in [[DataHolder sharedInstance]getFriendList]){
            [self.friendList addObject:user];
        }
        [self.tableView reloadData];
    }

}

Answer 1

使用NSNotificationCenter在数据下载完成后收到通知。在我看来，你使用Parse作为后端。

Answer 2

findObjectsInBackgroundWithBlock:是一种异步方法！在完成之前，您不会在friendList中拥有任何数据。

尝试使getFriendList异步。

- (void)getFriendListWithCallback:(CallbackBlock)callback {
    //...
    if (self.friendsList.count == 0) {
        [acceptedQuary findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
            if (error){
                self.friendsList = @[];
                NSLog(@"ERROR: %@ %@", error, [error userInfo]);

            } else {
                self.friendsList = [NSMutableArray arrayWithArray:objects];
                NSLog(@"Friend List from DataQuary %@", self.friendsList);
            }
            if (callback) callback(self.friendsList);
        }];
    } else {
        if (callback) callback(self.friendsList);
    }
}

使用单个数据源的多个UIView

2 个答案: