iOS4.0:UITextField出错的UIAlertView

UIAlertView *alert = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"Rank on ScoreBoard: %d",positionOnBoard] message:@"" delegate:self cancelButtonTitle:@"Dismiss" otherButtonTitles:@"Submit", nil];
nameField = [[UITextField alloc] initWithFrame:CGRectMake(12, 25, 260, 21)];

[nameField setBackgroundColor:[UIColor whiteColor]];
[nameField setPlaceholder:@"Your Name Here!"];

[alert addSubview:nameField];

[alert show];

[nameField becomeFirstResponder];

[alert release];

正如你所看到的,事情搞砸了。 它只发生在我的项目升级到ios4.0的时候。