iphone - Exc_Bad_Access 有时仅在显示警报视图时

Question

我有许多线程通过 performSeleactoreOnMainThread 方法调用以下函数：

-(void) showAlert: (NSString *)message{
if ([NSRunLoop currentRunLoop] != [NSRunLoop mainRunLoop]) {
    NSLog(@"<< perform in main thread>>");
    [self performSelectorOnMainThread:@selector(showAlert:) withObject:message waitUntilDone:NO];
}
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Info" message:message delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
}

因为，无论如何，这个方法只会在主线程上调用，我没有得到 EXC_BAD_ACCESS 崩溃的原因：[alert show]

而这种崩溃只是偶尔发生。请帮忙。

Answer 1

我猜你忘了添加return;你的代码，这样你的 if 下面的代码也会被执行，无论它是否在主循环中。

一个简单的解决方法可能是：

-(void) showAlert: (NSString *)message{
    if ([NSRunLoop currentRunLoop] != [NSRunLoop mainRunLoop]) {
        NSLog(@"<< perform in main thread>>");
        [self performSelectorOnMainThread:@selector(showAlert:) withObject:message waitUntilDone:NO];
        return;
    }
    UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Info" message:message delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
}

Answer 2

问题是由于 if 条件是 true 还是 false，alertview 显示方法将起作用。改变你的方法，如：

-(void) showAlert: (NSString *)message
{
 if ([NSRunLoop currentRunLoop] != [NSRunLoop mainRunLoop])
 {
    NSLog(@"<< perform in main thread>>");
    [self performSelectorOnMainThread:@selector(showAlert:) withObject:message waitUntilDone:NO];
 }
 else
 {
   UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Info" message:message delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
  [alert show];
 }
}

Answer 3

将 areturn放在 if 块的末尾：

-(void) showAlert: (NSString *)message{
if ([NSRunLoop currentRunLoop] != [NSRunLoop mainRunLoop]) {
    NSLog(@"<< perform in main thread>>");
    [self performSelectorOnMainThread:@selector(showAlert:) withObject:message waitUntilDone:NO];
    return;
}
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Info" message:message delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
}

Answer 4

替代为什么你不使用这个：

 [alert performSelectorOnMainThread:@selector(show) withObject:nil waitUntilDone:YES];

代替

 [alert show];