iPhone XCode使用未声明的标识符

Question

I just started programming in objective-c and I have a problem with "use of undeclared identifier 'uneImage'; did you mean '_uneImage'?". Lot of post speak about this but I haven't found the solution.

.h :

    #import 


    @interface ViewController : UIViewController 
    {
        UIImagePickerController *picker;
    }

    @property (weak, nonatomic) IBOutlet UIImageView *uneImage;


    - (IBAction)album:(id)sender;
    @end

.m

    #import "ViewController.h"

    @interface ViewController ()

    @end

    @implementation ViewController

    - (IBAction)album:(id)sender
    {
        picker = [[UIImagePickerController alloc] init];
        picker.delegate = self;
        picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
        [self presentViewController:picker animated:YES completion:nil];
    }

    - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
    {
        uneImage.image = [info objectForKey:UIImagePickerControllerOriginalImage];
        [picker dismissViewControllerAnimated:YES completion:nil];
    }

    - (void)viewDidLoad
    {
        [super viewDidLoad];
        // Do any additional setup after loading the view, typically from a nib.
    }

    - (void)didReceiveMemoryWarning
    {
        [super didReceiveMemoryWarning];
        // Dispose of any resources that can be recreated.
    }

    @end

Answer 1

When you define a property xyz , by default its name is transformed to _xyz to name its backing variable. You can override it with @synthesize name; or even @synthesize name = someOtherName; , but the use of @synthesize is no longer required.

The property itself is visible from the outside, but it does not introduce an unqualified name in the scope the same way the variables do. In other words, you cannot use the property without prefixing it with self , but you can use its backing variable.

To make the long story short, replace

uneImage.image = [info objectForKey:UIImagePickerControllerOriginalImage];

with

_uneImage.image = [info objectForKey:UIImagePickerControllerOriginalImage];

or

self.uneImage.image = [info objectForKey:UIImagePickerControllerOriginalImage];

to make it work.

Answer 2

You don't have an instance variable named uneImage . You have a property with that name and an automatically synthesized instance variable named _uneImage .

So change:

uneImage.image = ...

to either:

self.uneImage.image = ... // use the property

or:

_uneImage.image = ... // use the generated instance variable

Answer 3

您正在访问属性，因此需要在变量前放置“ self”：

self.uneImage.image = ....