Question

我试图在viewDidLoad中加载数据时显示一个指示器视图，但是在显示指示符之前加载开始，我猜这是因为直到之后才加载视图。我一直在读这个，但是无法让它发挥作用。

我想要的是在将文件加载到数据库期间显示活动指示器。

我一直在做测试，所以代码结构可能看起来有点奇怪。

有人可以请给我一个提示或链接，如何解决这个问题，以便在/如果数据从.txt文件加载到数据库中时显示活动指示符？

- (void)viewDidLoad {
[super viewDidLoad];
self.title = @" ";

loadActivityIndicator.hidden = TRUE;  // Hide UIActivityIndicationView at start



[self loadDataIfNeeded];
}

-(void)loadDataIfNeeded {
NSFileManager *fileManager = [NSFileManager defaultManager];

myFileArray = [[NSMutableArray alloc]init];

//======SET THE FILE INPUT NAME======//
qFileTxtName = @"110615";
[myFileArray addObject:qFileTxtName];
//===================================//

// CHECK IF THE FILE EXISTS
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:@"checkQuestionFile.plist"];

if([fileManager fileExistsAtPath:path]) {
    NSArray *readKeyFileName = [[NSArray alloc] initWithContentsOfFile:path];

    if ([[readKeyFileName objectAtIndex:0] isEqualToString:qFileTxtName]) {
        //==== THERE IS NO UPDATED QUESTION .txt FILE ====//
    }
    else {
        //==== THERE IS AN UPDATED QUESTION .txt FILE ====//

        //  SET UP UIActivityIndicator view to show that work is ongoing
        loadActivityIndicator.hidden = FALSE;
        [loadActivityIndicator startAnimating];


        //==== SET UP PATH FOR ALL FILES====//

        NSString *aString = [[NSString alloc]init];

        aString = [@"questions_famquiz_hard_" stringByAppendingString:qFileTxtName];
        NSString *path1 = [[NSBundle mainBundle] pathForResource:aString ofType:@"txt"];

        aString = [@"questions_famquiz_medium_" stringByAppendingString:qFileTxtName];
        NSString *path2 = [[NSBundle mainBundle] pathForResource:aString ofType:@"txt"];

        aString = [@"questions_famquiz_easy_" stringByAppendingString:qFileTxtName];
        NSString *path3 = [[NSBundle mainBundle] pathForResource:aString ofType:@"txt"];


        AccessQuestionsDB *accessQuestionDataFunction = [AccessQuestionsDB new];
        idCounter = [accessQuestionDataFunction populateTheDatabase: path1 theID:0 firstTime: YES];
        idCounter = [accessQuestionDataFunction populateTheDatabase: path2 theID:idCounter firstTime: NO];
        idCounter = [accessQuestionDataFunction populateTheDatabase: path3 theID:idCounter firstTime: NO];


        //==UPDATE THE PLIST==//
        [myFileArray writeToFile:path atomically: TRUE];

        //  Stop UIActivityIndicator as activity is over
        loadActivityIndicator.hidden = TRUE;
        [loadActivityIndicator stopAnimating];


    }



} else {
    //== If file not found write a new file ==//
    [myFileArray addObject:qFileTxtName];
    [myFileArray writeToFile:path atomically: TRUE];
}
}

问题已解决

我替换了电话

[self loadDataIfNeeded];

用;

[NSThread detachNewThreadSelector：@selector（loadDataIfNeeded）toTarget：self withObject：nil];

根据约拿的建议实现多线程： - ）

Answer 1

您正在主线程中同步加载数据。这意味着主线程，即负责绘制UI的主线程，正在忙于加载您的数据，并且在您的loadDataIfNeeded方法完成之后将无法更新您的视图（此时您不希望显示您的活动指示器无论如何都可见。）

在主线程上显示活动指示符，然后允许主线程的运行循环继续，而是在辅助线程上异步执行昂贵的操作（如加载数据或执行网络请求）。

查看NSThread，NSObject的{{1}}和-performSelectorInBackground:withObject:，了解从主线程执行任务的不同选项。

Answer 2

Matt Drance撰写的“IOS Recipes”一书讲述了如何做到最好。您可以在http://media.pragprog.com/titles/cdirec/activity.pdf

的书中免费摘录此食谱

您可以在http://pragprog.com/titles/cdirec/ios-recipes

的图书页面上找到该食谱的源代码

Answer 3

在viewDidLoad中添加

    UIActivityIndicatorView *activityView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
    activityView.frame = CGRectMake(0, 0, 44, 44);
    activityView.center = self.view.center;
    activityView.tag = 99;
    [activityView startAnimating];

    [self.view addSubview: activityView];

    [activityView release];

然后在加载方法完成加载后，只需从超级视图中删除活动指示器。

在加载add

后的loadDataIfNeeded中

[[self.view viewWithTag:99] removeFromSuperview];

如何在加载数据时显示UIActivityIndicationView

3 个答案:

如何在加载数据时显示UIActivityIndi​​cationView

3 个答案:

如何在加载数据时显示UIActivityIndicationView