Can I just omit the parameter completely? I cannot seem to find a use for it within my IBAction method.
Yes, you can omit it if you don't want it:
-(IBAction)action{
// some stuff
}
Although it can come in handy in a lot of situations
Source : Apple Doc
Related
Is there any sort of flag or way to call a method without triggering any event handlers?
FOR EXAMPLE
I'm handling a controlTextDidChange method and checking to see if the character returned by a keystroke is valid. If it's not, I remove it; if it is, I append a word. The problem is that when I change the text while in controlTextDidChange, controlTextDidChange is called again and the program will loop indefinitely. I know I can use an instance variable to get around this, but is there any sort of flag or way to call a method without triggering any event handlers?
To expand the comment into a quick answer.
You have a method that issues a notification by design. You want it to not issue that notification. You don't have an alternative available that does the same thing w/o the notification. If you want it to never issue that notification, and you have access to the code for the method, you could swizzle the method to a version where you've just commented out the notification. Of course, if you had the code, you could just add another method, and call that one. So you don't have the code, and all that's moot.
Can't you just bracket that invocation in code that removes the listener and then restores the listener? In other words, psuedocode like this:
[self.controlThingy removeObserver:self]
[self.controlThingy myMethod]
[self.controlThingy addObserver:self]
You've then made self deaf to notifications for that one invocation of myMethod. I've done similar things with bindings and KVO.
I've seen a lot of discussions NEAR this subject, but none that actually work in Xcode 5.x, especially using ARC. I have a simple problem:
I need to pass a method reference to a CreateButton method so that when the button is called it calls my custom function, and not some generic one.
I've tried using (SEL) type, but that doesn't work with ARC. I've tried using the &func method, but that claims I haven't declared the function yet.
So my need is:
Class A calls Class B and sends over the info to make a UIButton. Within that call, I want to send over the action:method in a reference. I'm sure this is done routinely, but I can't seem to find an iOS 7 / Xcode 5.x method of doing it. I've also reviewed the O'Reilly iOS 7 fundamentals and cookbook code and couldn't find this discussed anywhere.
Thanks for you help.
When I have to pass selectors around, I convert them to strings with NSStringFromSelector() and back to selectors with NSSelectorFromString().
Passing the strings around is a lot easier. You can store them in collections (arrays, dictionaries), serialize and unserialize them, and they will work naturally with ARC.
Example:
In your class A where you gather the information to create a button:
NSString *selectorString = NSStringFromSelector(#selector(yourActionMethodNameHere:));
// Gather more information needed by Class B here, then package
// it all up into a dictionary, for example
NSDictionary *buttonInfo = #{#"selectorString": selectorString, /* more stuff here */};
At this point, you can call your button-constructing method in Class B, passing along buttonInfo, which contains all the information that that helper method needs, including the selector. The method can convert the string back to a selector and use it like this:
SEL actionSelector = NSSelectorFromString(buttonInfo[#"selectorString"]);
// configure your button to use actionSelector here
You should be able to use SEL parameters? I know I have done before.
ARC might complain and give you a warning, but it won't fail to compile. It's simply a warning because it can't quite figure out what to do memory wise.
If you really can't get that to work though, another alternative would be to use a block, so you might call your method like
[objectA performMethodWithParam:paramA paramb:paramB completion:^{ ... do somethhing ... }];
Then in that method you can just call
completion();
Instead of actually calling a method.
Another alternative would be to use the delegate pattern. Create a #protocol defining a method such as classADidFinish then make class B implement that method. Then set the instance of classB as the delegate for your classA instance, and have it call that method when it's done.
Both of these approaches will stop ARC moaning at you.
But as I said, using SEL params should work fine. There is a way you can even get the compiler to stop showing you the warnings but it's a little ugly.
I'm just beginning with ObjC. I'm wondering how to find out when looking at code, written by me or from a template that comes when you use the wizard to create a new class, how you can tell if a method is overriding something.
In Java, you can mark a method with #Override, and then it's very easy to see if it's overriding something. That's not foolproof, because #Override is optional, but if I'm still unsure I can just type that in and see if it generates an error.
Is the only way to look up the source of the superclass, or in the case of a framework to read the documentation?
I don't know a way to see this immediately, but you could check if super responds
to the same selector. Example:
- (void)myMethod
{
// Temporarily add this line. If the compiler does NOT complain,
// "myMethod" overrides a method from some superclass.
[super myMethod];
// ...
}
You can use instancesRespondToSelector to see if your instance has an implementation of the method in its object hierarchy.
[MyClass instancesRespondToSelector:#selector(myMethod)];
or depending on what type of checking you need to do
[MyClassSuperClass instancesRespondToSelector:#selector(myMethod)];
I'm new to programming in Cocoa, so I'm still struggling to grasp some basic concepts.
What I want to do (as an example) is write an application with multiple NSTextFields. However, these NSTextFields need to be linked to separate classes. Additionally, each separate class needs to be able to get and set data from each other.
I tried to add methods to tackle this problem, to no avail. Let's say this is a method in the textbox's original class, and I want to call it from another class.
-(void)settextfield:(NSString*)stringy;
{
[TextField setStringValue:stringy];
}
Here's the calling code (we're calling this from another class, TestClass)...
-(IBAction)test:sender;
{
[BundleBrowseTextBox settextfield: #"Testy"];
}
Nothing happens. There's probably some obvious way to do this, but I haven't been able to unearth this via Google searches.
My mistake was that I was calling the class method instead of the instance... you can call the instance via IBOutlets and defining those outlets properly in Interface Builder.
You need to make sure the pointers you are using are not nil.
One odd/convenient thing about objC is that you can pass messages to nil and it won't crash.
If I'm right in assuming you're trying to set the text in an instance of BundleBrowseTextBox, you should call the settextfield: message on the instance name, rather than on the class name (if BundleBrowseTextBox IS the instance -- rather than the class -- you should really avoid capitalized instance names for clarity). i.e.:
-(IBAction)test:(id)sender;
{
// Assuming bbtBox is defined as an instance of BundleBrowseTextBox
[bbtBox settextfield: #"Testy"];
}
I believe you forgot your parameter type in your original post
this...
-(IBAction)test:sender;
{
[BundleBrowseTextBox settextfield: #"Testy"];
}
should be
-(IBAction)test:(id)sender;
{
[BundleBrowseTextBox settextfield: #"Testy"];
}
That aside if you understand the difference between class and instance as you say you do.
Then it would be nice if you would show us the rest of your implementation and interface.
The problem is probably not in the code snippets you showed us.
I see two approaches to handling sender objects in IBAction statements. The first looks like this:
-(IBAction)buttonPressed:(id)sender{
UIButton*someButton=(UIButton*)sender;
//do something with someButton.tag or whatever
}
Another seems easier:
-(IBAction)buttonPressed:(UIButton*)sender{
//do something with sender.tag or whatever
}
I generally opt for version 2. Any particular reason to prefer one style over the other, if you know that only a button will be sending to this method?
I can see where version 1 is good if anything can be a sender, like a button, or switch or slider, etc. But if you are looking for UIButton properties like tag it won't make much difference if your sender is not a UIButton. So version 2 seems a lot more straightforward.
Just thought I'd see if I'm missing an obvious reason to prefer version 1.
I see no problem using the second version. I usually use the second version, only using the first version if the sender may be more than one type of object. Then, if the method needs to know what type of object, the method can query the sender before casting the sender to a particular type.
Even more frequently I find no need to access the sender, so I just use:
- (IBAction)buttonPressed {
// Do something.
}