Question

我有很多线程通过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： [提示显示]

这种崩溃有时只会发生。请帮忙。

Answer 1

我想您忘记在代码中添加return;，以便if下面的代码也可以执行，无论它是否处于主循环中。

一个简单的修复可能是：

-(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return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

替代方案为什么不使用它：

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

而不是

 [alert show];

Exc_Bad_Access有时仅显示警报视图

4 个答案: