场景是这样的，点击按钮，开辟新线程，弹出alertView。然后调用dismissWithClickedButtonIndex让其消失。

1 /** 定义按钮 */ 2 -(void)setupAllBtns{   3     UIButton *btn2 = [UIButton buttonWithType:UIButtonTypeRoundedRect]; 4     btn2.frame = CGRectMake(100, 140, 100, 50); 5     [btn2 setTitle:@"读取信息" forState:UIControlStateNormal]; 6     [btn2 setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal]; 7     btn2.backgroundColor = [UIColor brownColor]; 8     [btn2 addTarget:self action:@selector(readSimWithNewThread) forControlEvents:UIControlEventTouchUpInside]; 9     [self.view addSubview:btn2];10 }11 12 -(void)readSimWithNewThread{13     NSThread *button3Thread = [[NSThread alloc] initWithTarget:self selector:@selector(readInfo) object:nil];14     [button3Thread setName:@"thread-3"];15     [button3Thread start];16 }17 18 /** 新线程读取信息 */19 -(void)readInfo{20     [[NSOperationQueue mainQueue] addOperationWithBlock:^21      {22          self.mAlertView = [[UIAlertView alloc] initWithTitle:nil message:@"开始读取，请稍候..." delegate:self cancelButtonTitle:nil otherButtonTitles:nil, nil];23          [self.mAlertView show];24      }];25     26     char sn[64] = {
   0};27     int ret = [self.sim GetInfo:sn];28     29     //alert消失的方法30     if (self.mAlertView.visible) {31         [self.mAlertView dismissWithClickedButtonIndex:0 animated:YES];32     }33     34     NSString *msg = @"";35     msg=[NSString stringWithFormat:@"MobileNum=%@",[NSString stringWithUTF8String:sn]];36 }

但有时会出现alert界面一直出现，造成界面卡死。

原因在于由于用多线程，线程阻塞时，调用alert消失时，alertView还没有绘制出来。当alertView绘制出来时，alert消失的方法已经过时。

解决方法是在执行alert消失的方法时，让线程暂停一段时间。如0.5s

[NSThreadsleepForTimeInterval:0.5];

或是用

[self performSelector:@selector(dimissAlert) withObject:alert afterDelay:2.0];//将其添加在[self.mAlertView show]之后-(void)dimissAlert{    if (alert.visible) {        [alert dismissWithClickedButtonIndex:0 animated:YES ];    }}

这样在固定时间后，alert总会消失。