iphone - 我应该为“无价值”声明写什么？

Question

我是 xcode 的初学者。如何为尚未完成写入信息或在 UILabel (labelDate) 中没有值的内容编写代码，然后弹出 UIAlertView 告诉您是否尚未输入信息？

我的 UILabel 从下面的代码中获取输入

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
    year = [picker selectedRowInComponent:0];
    month = [picker selectedRowInComponent:1];
    day = [picker selectedRowInComponent:2];
    date = @"";
    if(viewPicker.tag == 1)
        labelDate.text = [date stringByAppendingFormat:@"%d:%d:%d", year , month, day];
    else
    ... etc
}

我的按钮是这样的

- (IBAction)readyBtn:(id)sender { 
    if ( ??? ) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Alert" message:@"Please input date" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
    }

我已经尝试过这样写，但我认为这不是一个好主意，因为如果年、月、日选择为 0，则会弹出 uialertview。

- (IBAction)readyBtn:(id)sender { 
    if (viewPicker.tag == 1) {
        year = month = day = 0;
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Alert" message:@"Please input date" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
    }

谢谢你教我。

Answer 1

如果您想检查您的 UILabel 是否没有价值，请在您的函数中执行以下操作

- (IBAction)readyBtn:(id)sender { 
    if ( [yourLabel.text isEqualToString:@""]) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Alert" message:@"Please input date" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
    }

Answer 2

检查输入的日期是否为零，如果为零则弹出警报视图。或者

if(entereddate.text isEqualToString:" ")
{
       UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Alert" message:@"Please input date" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
            [alert show];

}

Answer 3

您的 Button 事件将是这样的：

 - (IBAction)readyBtn:(id)sender 
 { 
    if ( labelDate.text.length >0 ) // Add OR condition for any other lablel or textField
    {
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Alert" message:@"Please input date" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
    }
}