如果UITextField為空，則顯示UIAlert

Question

我要做的是，如果UITextField上沒有任何內容，則應用程序將顯示警報。 我不明白我在做什么錯。 這是我的代碼：

- (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

嘗試使if語句中的每個子句都明確-僅出於可讀性考慮...

我會在測試中使用邏輯或，而不是邏輯與。 這樣，如果任一文本字段為空，警報將顯示

    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];
    }

Answer 2

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

Answer 3

我假設addText是您的tesxField，所以您還需要設置條件[addtake.text length] == 0。