Question

我想首先显示视图，然后在后台线程中加载数据。当我从根控制器导航到视图控制器时，我想先显示视图。截至目前，它一直停留在根控制器上，直到加载视图控制器。这是我的根控制器代码。

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath 
{   
ProductDetailViewController *tempProductDetail = [[ProductDetailViewController alloc] init];

[self.navigationController pushViewController:tempProductDetail animated:YES];

[tempProductDetail release];
}

ProductDetailViewController，这里我想首先显示视图，然后加载数据......

- (void)viewWillAppear:(BOOL)animated{
[super viewWillAppear:YES];
[self performSelectorOnMainThread:@selector(workerThread) withObject:nil waitUntilDone:NO];
}

-(void) workerThread{

NSAutoreleasePool *arPool = [[NSAutoreleasePool alloc] init];
[arPool release];
}

不知道我做错了什么。请帮忙。

Answer 1

使用[self performSelectorInBackground:@selector(workerThread) withObject:nil];代替

[self performSelectorOnMainThread:@selector(workerThread) withObject:nil waitUntilDone:NO];

Answer 2

找到了这个问题的答案，

- (void)viewWillAppear:(BOOL)animated{
[super viewWillAppear:YES];
[self performSelectorInBackground:@selector(workerThread) withObject:nil];
}

- (void) workerThread
{
// Set up a pool for the background task.
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];

// only do data fetching here, in my case from a webservice.
//...

// Always update the components back on the main UI thread.
[self performSelectorOnMainThread:@selector(displayView) withObject:nil waitUntilDone:YES];

[pool release];
}

// Called once the background thread task has finished.
- (void) displayView
{
//here in this method load all the UI components
}

Answer 3

考虑使用以下模式代替线程，在我看来它更清晰：

- (void)viewWillAppear:(BOOL)animated 
{
   NSInvocationOperation *operation = [[NSInvocationOperation alloc] 
                                       initWithTarget:self 
                                       selector:@selector(someFunction) 
                                       object:nil];
   [[NSOperationQueue currentQueue] addObject:operation]; // this will actually start the thread
   [operation release];
}

- (void)someFunction 
{
   // don't need to initialize and release an autorelease pool here,
   // you can just write a function as usual ...

   [self updateUI];
}

- (void)updateUI 
{
   if (![NSThread isMainThread]) // if we need a UI update, force it on main thread
   {
      [self performSelectorOnMainThread:@selector(updateUI) withObject:nil waitUntilDone:YES];
      return;
   } 

   // do UI updates here
}

通过以这种方式编写代码，您可以更加动态地决定要线程化的函数，因为没有自动释放池要求。如果您需要进行UI更新， updateUI 函数将确保它自己在主线程上运行，因此调用者不需要考虑这一点。

iphone，后台线程无法正常工作

3 个答案: