为什么在Xcode中看到“未声明的标识符”？

Question

I recently started a book knowing nothing about Macs or Xcode called Beginning iOS 5 Development . I'm in chapter 4 and either I made a mistake or they made a typo. I cannot figure it out, so here's the problem:

- (IBAction)textFieldDoneEditing:(id)sender {
    [sender resignFirstResponder];
}


-(IBAction)backgroundTap:(id)sender {
    [nameField resignFirstResponder];
    [numberField resignFirstResponder];
}

- (IBAction)sliderChanged:(id)sender {
    UISlider *slider = (UISlider *)sender;
    int progressAsInt = (int)roundf(slider.value);
    sliderLabel.text = [NSString stringWithFormat:@"%d", progressAsInt];
}

@end

They told me to add the bold text after the sliderChanged method. Now Xcode is saying "use of undeclared identifier" so I can't run the app to preview on the iOS simulator. BTW, it says the problem is the sliderLabel.text .

Answer 1

确保头文件的接口声明中具有IBOutlet UILabel *sliderLabel （并且已将其连接到视图中的标签）。

Answer 2

Second paragraph of page 98 describes how to name the label "sliderLabel". The label itself was created in the last paragraph of page 96. The critical thing here is to inspect the property of the label in assistant editor, and change the "Name" field of the label widget to "sliderLabel".