我用UIAlertViewStylePlainTextInput风格显示UIAlertView。然后我尝试像这样验证空字段:-(void)alertView:(UIAlertView*)alertViewclickedButtonAtIndex:(NSInteger)buttonIndex{if(buttonIndex==1){if([[alertViewtextFieldAtIndex:0].textlength]>0||[alertViewtextFieldAtIndex:0].text!=nil||[[alertViewtextFieldAtIndex:0].textisEqua