相关疑难解决方法(0)

我是Objective C的新手,来自.NET和java背景.

所以我需要异步创建一些UIwebviews,我在自己的队列中使用

     dispatch_queue_t queue = dispatch_queue_create("myqueue", NULL);
     dispatch_async(queue, ^{
        // create UIwebview, other things too
             [self.view addSubview:webView];
        });

正如你所想象的那样会抛出一个错误:

   bool _WebTryThreadLock(bool), 0xa1b8d70: Tried to obtain the web lock from a thread other  
   than the main thread or the web thread. This may be a result of calling to UIKit from a  
   secondary thread. Crashing now...

那么如何在主线程上添加子视图呢？

相关：可以在后台线程上创建 UIView 吗？

这个后台线程代码安全吗？

let viewController = MyViewController(nibName: nil, bundle: nil)
viewController.title = "My Title"
viewController.myProperty = true
dispatch_async(dispatch_get_main_queue(), {
    self.navigationController?.pushViewController(viewController, animated: true)
})

我想在线程中加载一些视图以避免UI冻结等待加载结束.

我不习惯穿线,所以我做了一个快速测试.我的代码只是尝试在线程中创建视图,并在主线程的当前viewcontroller视图中添加此视图.

我的UIView正在工作,但对于我的UILabel,我必须等待20-60秒才能将它放在屏幕上.

我使用UIButton进行测试,在这种情况下,按钮会立即显示,但按钮内的标签显示的延迟与我的UILabel相同.

让它按我想要的方式工作的唯一方法是添加一个[lbl setNeedsDisplay]; 在主线程中强制UILabel立即显示.为什么？没有这条线可以完成这项工作吗？

    dispatch_queue_t queue = dispatch_queue_create("myqueue", NULL);
dispatch_async(queue, ^{

    // NEW THREAD
    UILabel *lbl = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 100, 48)];
    lbl.text = @"FOO";

    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 40, 40)];
    view.backgroundColor = [UIColor redColor];

    // MAIN THREAD
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.view addSubview:lbl];
        [lbl setNeedsDisplay]; // Needeed to see the UILabel. WHY???

        [self.view addSubview:view];
    });
});
dispatch_release(queue);

我读了一些UI接口只在MainThread上更新的信息.

我需要异步更新一些UIButtons,所以我使用performSelectorInBackground它,它在模拟器和设备(iPad4)上工作正常.

[self performSelectorInBackground:@selector(toggleToUpperWhenSingleShift) withObject:nil];

- (void)toggleToUpperWhenSingleShift{
    shiftStateIndicator = 1;
    for (UIView *aPad in self.subviews) {
        if ( [aPad isKindOfClass:[UIButton class]] ) {
            UIButton *aButPad = (UIButton *)aPad;
            NSMutableString *currentTitle = [NSMutableString stringWithString:[aButPad titleForState:UIControlStateNormal]];
            NSString *firstChar = [currentTitle substringToIndex:1];
            [currentTitle replaceCharactersInRange:NSMakeRange(0, 1) withString:[firstChar uppercaseString]];
            [aButPad setTitle:currentTitle forState:UIControlStateNormal];
            [aButPad setTitle:currentTitle forState:UIControlStateHighlighted];

            currentTitle = [NSMutableString stringWithString:[aButPad titleForState:UIControlStateSelected]];
            firstChar = [currentTitle substringToIndex:1];
            [currentTitle replaceCharactersInRange:NSMakeRange(0, 1) withString:[firstChar uppercaseString]];
            [aButPad setTitle:currentTitle forState:UIControlStateSelected];
        }
    }
}

我担心如果我保留我的代码会发生一些不需要的功能.谁能解释一下我的细节performSelectorInBackground？

为什么不用它来更新UI以及为什么我的应用程序没问题？无论如何调试问题都会欣赏!

HomeViewController.h

#import "DataParser.h"
@interface HomeViewController : UIViewController <DataParserDelegate>
{
    UILabel *theLabel;
}

HomeViewController.m

#import "HomeViewController.h"
@implementation HomeViewController
-(void)viewDidLoad
{
    theLabel = [[UILabel alloc] initWithFrame:CGRectMake(200, 200, 100, 30)];
    theLabel.text = @"Bob";
    theLabel.font = [UIFont italicSystemFontOfSize:20.0];
    theLabel.textColor = [UIColor whiteColor];
    theLabel.backgroundColor = [UIColor blueColor];
    [self.view addSubview:theLabel];

    UIButton *theButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [theButton addTarget:self action:@selector(clicked:) forControlEvents:UIControlEventTouchUpInside];
    [theButton setTitle:@"Big Button" forState:UIControlStateNormal];
    theButton.frame = CGRectMake(100,100,200,50);
    [self.view addSubview:theButton];
}
-(void)clicked:(id)sender
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND,0),
    ^{
        DataParser *data = [[DataParser alloc] init];
        data.delegate = self;
        [data loadSomething];

        dispatch_async(dispatch_get_main_queue(),
        ^{ …