Objective-C-需要知道如何向按钮添加另一个目标

Question

So I have 2 classes(FirstClass and SecondClass). FirstClass is a UIViewController, and secondClass is a NSObject class. In the FirstClass i have a button -- dialButton.

In the SecondClass, I call a method that I made in the FirstClass (changeMethod)

This Method changes the Method that the button will call when clicked. The Method it changes to is a method in the SecondClass (secondClassMethod).

This changeMethod does exactly this:

[dialButton addTarget:secondClass selector:@selector(secondClassMethod)         
forControlEvents:UIControlEventTouchUpInside];

By the way, dialButton is a static button. What am I doing wrong

Edit: I fixed the problem above, but now my problem is this:

The button's target method is changed, but the target method isn't called.

I call the method printPrompt from the SecondClass.

printPrompt:

FirstClass *firstClass =[[FirstClass alloc]init];
[firstClass test];

test:

SecondClass *secondClass = [[SecondClass alloc]init];
[dialButton removeTarget:self selector:@selector(firstClassMethod) forControlEvent: UIControlEventTouchUpInside];
[dialButton addTarget:secondClass selector:@selector(secondClassMethod)         
forControlEvents:UIControlEventTouchUpInside];

secondClassMethod is not called when i click the button after calling test.. rather, the program crashes.

secondClassMethod: FirstClass *firstClass = [[FirstClass alloc]init]; [firstClass setString: @"Test"];

setString just changes a UIText Field. I've tested it and setString: works.

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Answer 1

The code you posted will add an additional target/action to the button. Buttons can call multiple methods in multiple targets when they are tapped.

If you want to replace an existing target/action with another one, you have to first remove the existing target/action using the removeTarget:action:forControlEvents: method, then add the new target/action with the code you posted.