我是否可以为直到在OC中运行才指定的类设置属性？

Question

I've got a fixed controller with dynamic views as its view. I want to set value for property of a certain view.

Here's code in the controller as below:

@property (nonatomic, retain) Class viewClass;

- (void)viewDidLoad {
        [super viewDidLoad];
        // Do any additional setup after loading the view.
        self.view =  _viewClass.new;
        if ([_viewClass resolveInstanceMethod:@selector(lineAdded)]) {
            [_viewClass setValue:@YES forKey:@"lineAdded"];
        }
        self.view.backgroundColor = [UIColor whiteColor];
}

In * the certain* view, I've got a property like this.

@property (nonatomic, assign) BOOL lineAdded;

It reminds me

Undeclared selector 'lineAdded'

When I run, it just skip if condition and go on.

My question is: is it impossible to set property when the class it belongs to isn't specified?

Hope somebody could help me. Thanks in advance.

Answer 1

When you are setting value of @YES . You should declare that as NSNumber instead of using primitive data type: BOOL . When you retrieve, you should use -(BOOL)boolean method to retrieve it. As for the resolveInstanceMethod , I think you should look into this documentation to make sure that's the correct logic you are putting in.

https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtDynamicResolution.html

Answer 2

You can get rid of the warning by making the compiler see a declaration of the lineAdded selector. Either #import a header file that contains a declaration of that property, or declare it another way, for example like this:

@protocol DummyProtocol
@property (nonatomic, unsafe_unretained) BOOL lineAdded;
@end

Second, setting the value of the property doesn't require the lineAdded selector. It requires the setLineAdded: selector.

Third, the proper way to check whether self.view responds to setLineAdded: is to ask it, like this:

    if ([self.view respondsToSelector:@selector(setLineAdded:)]) {
        [self.view setValue:@YES forKey:@"lineAdded"];
    }

Fourth, you were asking _viewClass whether its instances respond to lineAdded , but then you were asking the _viewClass object itself (rather than the self.view instance of it) to set its own lineAdded property. I fixed that in my code above.

Fifth, you should assign to self.view in loadView , not in viewDidLoad .

If, after all that, it's not setting lineAdded , then your view (whatever class you chose) simply doesn't respond to setLineAdded: .