iphone - 如果 UITextField 为空则显示 UIAlert

Question

我只想做，如果 UITextField 上没有任何内容，应用程序将显示警报。我不明白我在做什么错。这是我的代码:

- (IBAction)Calculate:(id)sender {
    /*If there is nothing on textfield, it will show an alert*/

    if ([addtake.text length] && [Subtake.text length] == 0) 
    {

            UIAlertView *myAlert = [[UIAlertView  alloc]initWithTitle:@"Alert"message:@"Empty   TextField not allowed" delegate:nil cancelButtonTitle:@"Okay" otherButtonTitles: nil];    
            [myAlert show];
    }

    else{

            NSString *Adding =[addtake text];
            NSInteger number = [Adding intValue]; /*Converting String to int*/
            NSInteger new = 5 + number;
            NSString *newString = [NSString stringWithFormat:@"%d",new];
            [myAdd setText:newString];
            /*Subtruct*/
            NSString *Subtruct =[Subtake text];
            NSInteger SubNumber = [Subtruct intValue];
            NSInteger newSub = 10 - SubNumber;
            NSString *newSubString = [NSString stringWithFormat:@"%d",newSub];
            [mySub setText:newSubString];

            [addtake resignFirstResponder]; 
            [Subtake resignFirstResponder];        
      }
  }

Answer 1

尝试使您的 if 语句中的每个子句显式 - 如果只是为了可读性...

我会在您的测试中使用逻辑 OR，而不是逻辑 AND。这样，如果任一文本字段为空，就会显示警报

    if ((![addtake.text length]) || (![Subtake.text length])) 
    {

            UIAlertView *myAlert = [[UIAlertView  alloc]initWithTitle:@"Alert"message:@"Empty   TextField not allowed" delegate:nil cancelButtonTitle:@"Okay" otherButtonTitles: nil];    
            [myAlert show];
    }