I know the differences between IBAction and IBOutlet, but I don't know when I should use one over the other.
For example, I'm trying to make a calculator. I have ten buttons and one label to display a result. Must I create ten IBOutlets in my interface? If not, why not?
An IBOutlet is a connection to an object, and an IBAction is a connection to a method to be invoked as a callback. For example, you might have ten buttons and one label, but you might connect to the label using an IBOutlet (so you can update its value), and a single function - (IBAction)buttonPressed:(id)sender; that is connected to the onTouchUpInside event of each of the ten buttons. The buttonPressed: method's implementation will then need to inspect the sender to figure out what its value is.
You should not need to have an IBOutlet for each button if this is all you need to do.
Ok, IBOutlets and IBActions serve two separate purposes.
IBActions are basically methods that can be connected to UI elements through IB. They provide ways for your object to be notified when something has happened with the UI. They also provide the sender argument when they are called so that you can access the UI Element that sent the message from within the method.
An IBOutlet on the other hand offers a way to get a reference to the UI element within your code at any point, it is used when you need to change aspects of the UI.
For your situation you don't really need to have IBOutlets for the buttons because you don't need to change anything about them, you just need to be notified when they have been pressed.
As a note, if you have that many buttons, and you for some reason needed a way to access them from within your code to change something about them i would not recommend using 10 IBOutlets. Instead, i would use the viewWithTag: method, and set each buttons tag accordingly so that you don't have to go to the trouble of creating IBOutlets for each one.
In your case, I would create one IBOutlet for the label, and one IBAction for the buttons. The IBOutlet for the label would be to update the text when the user pressed a button. Your IBAction would look something like this:
-(IBAction)digitPressed:(UIButton *)sender{
//First you have to check if there is currently any text in the label
//If there is not, the below line of code is performed
NSString *textWithDigit = [[yourLabel.text] stringByAppendingString: sender.titleLabel];
//This line updates the label's text
label.text = textWithDigit;
}
I only put in the code relevant to IBActions and IBOutlets (you need an IBOutlet for the label in order to update the text, and you need the IBAction to change the label's text to the digit pressed); there is much more code needed (code needed to check if the user is currently in the middle of typing a number, code for operations like +, -, *, /), but this was just a start.
Hope this helps!
Related
I have an app that contains an NSTableView instance with 2 columns. One column, is an instance of this:
#import <Cocoa/Cocoa.h>
#class NSTableView;
#interface MMCheckboxTableCellView : NSTableCellView
#property (weak) IBOutlet NSButton *checkboxField;
#end
and the implementation is all boilerplate with no custom code added at all. In code, the NSTableView instance sets tableview.enabled = YES (or NO) programmatically based on various state of the app. When tableview is disabled, the other column of the table, which is display only, stops responding to click actions, as expected. The checkbox column, above, continues to respond to clicks and lets the user check/uncheck the button instances.
To try to troubleshoot this, I added a Text Field (it's not hooked up to anything) in the the checkbox column and when the tableview is disabled, it isn't possible to enter text into the field. Is there something special about NSButton that I'm missing? Is it possible that because I derived this class from NSTableCellView with an added Check Box rather than using a Check Box Cell I'm running into this problem?
I finally figured this out. It appears that even though the NSButton is embedded in the NSTableView, setting enabled=NO on the table doesn't control the behavior of the button. The only thing that eventually made this work was to invoke setEnabled the the control based on the state of the app. This had to happen in the rendering of the cell, so when the state changes, it was also necessary to invoke NSTableView:reloadData so the visible cells would redraw immediately.
As an alternative, I decided to work around this same problem by setting up a computed property matching to my boolean property that returned either a blank or a checkmark character (✓). Then bound to this field as a normal NSTextfield for which the enabling/disabling works.
// Swift
// Computed variables on model for readonly display in table
var bIosText:String {return bIos ? "✓" : " " }
var bAndroidText:String {return bAndroid ? "✓" : " " }
Looks pretty good I think:
Of course this is only part of the solution, if you want to enable editing, you need to have multiple columns and hide/unhide as needed.
Do not embed an NSButton in the table view, only use a NSButtonCell. If your NSTableView was view based, it will switch to cell based (at least Xcode did that for me).
So this is wrong:
And this is right:
It should suffice to disable/enable the table view after this change, the button cell will behave accordingly.
I've got an Custom UIButton. It's got
a "static" background image
a variable text (the Title) which gets set in the code
Now I would like to add an icon (UIImage/UIImageView) inside the button on the left of the text. (I use the indent to move the text slightly to the right). Is there an easy way of adding that icon (and referencing it from code, so I can change it) or would you recommend creating a completely new button e.g. based on a UIView? (e.g. a view, that responds to touches)?
I'm just trying to get a feel for what the best approach would be for this. Any experience?
Two ways:
I prefer doing this by subclassing a UIView and (as you mention) implement the UITouch-responder methods. You're also able to override drawRect: what I really like because it makes your app soooooo much faster!
Since UIButton is a subclass of UIView, you can add a UIImageView to your button by using addSubview:. If you save it in your main-class (#property (...) UIButton *button) you can always access it by calling [self button]. You can also subclass your UIButton and add this #property. That's up to you.
It's totally up to you. However I prefer the first way!
I have an IBOutlet assigned in my header file named *myButton and is type UIButton class.
the purpose of myButton is to programmatically assign the alpha to multiple buttons.
it seems as if you can only assign myButton to one button in IB.
is there a way to assign an alpha value to multiple buttons at the same time or am i going to have to refer to each button. ive got quite a few buttons and i need them all to change at the same time.
thanks for any help!
An IBOutlet is simply an instance variable (which is a pointer) in your class. You cannot have a pointer refer to more than one memory space simultaneously in any programming language.
You will need to refer to each button individually. You could look into storing pointers to all your buttons in an NSArray and simply iterating over it. You could also look into using an NSMatrixView or NSCollectionView to display your many buttons, and then take action on that to change all your buttons.
If I name a widget in Interface Builder, and then I write a method that receives click events on that button:
- (IBAction)btnTouchDown:(id)sender
{
// how can you identify the button here,
// if several different buttons map
// their "Touch" event to this same function?
// I know you can look at its text but that seems really clumsy
// can I somehow get its INTERFACE BUILDER NAME?
// I named each uniquely in interface builder,
// under "Identity"/"Name"
// Or is my only recourse to tie EACH BUTTON to its own handler function?
}
Click on the button in interface builder, press CMD+2 (Or in info dialog, second tab) and drag the circle from Touch up inside to File's Owner from the yourView.xib window and then it'll let you select one of the methods which has the - (IBAction) method:(id)sender signature. Choose the one you want to associate with that button :)
You say you don't want to make a method for each button, but actually that is the best way in my opinion, rather than having one huge monolithic method which handles each of the buttons and checks each time to see which one of them it is. Using the process I mentioned above, you can specifically tie a handler method to a particular button, keeping things nice, tidy, and logical.
If you really want to do that though, you can also test for the tag number.
you have to define the button as an instance variable in your view controller and then use the IBOutlet pragma to make it known to IB. So for example you would do this in your view controller:
UIButton IBOutlet *mybutton;
After defining it like this it will show up in your IB connections where you can associate it with the appropriate button
Here's a simplification:
I have an application with several buttons. If it is the first time the application is launching, I want to do some special things. In my AppController class, which is a delegate of NSApp, I use the delegate method -applicationDidFinishLaunching: to perform the test. After I've detected that it is the first time, I first want to access some IBOutlets. Then, I'd like to be able to get mouse events for each button, so that I can do other things.
I can't figure out want to do with the classes. I'd like to make a new class (FirstLaunch) for the first launch, but I'm not sure what to call from AppDelegate. Also, to get mouse events, shouldn't I be a sublass of the buttons, and considering that I have multiple buttons, I'm confused. I could probably tackle these issues one-by-one, but taken all together, they're confusing me.
Broken down, I need to access & manipulate IBOutlets I have set in IB, determine when buttons are clicked (and which button was clicked). I'd like to be able to do this from another class so as to not clutter up the AppDelegate.
Thanks for the help!
To be more clear, what I'm actually trying to do is to use Matt Gemmel's MAAttachedWindow to put up a help bubble by a button. When the button is clicked clicked, the bubble disappears and another one is put somewhere else. The bubbles will be attached to controls in the main window.
I'm guessing you want to show some additional user interface on the first launch? If it's a separate window, I'd advise creating a subclass of NSWindowController. Add a new NIB file for the first-run user interface to your project and change the class of the File's Owner object to FirstLaunch. Control-drag a wire from the File's Owner delegate onto the window to connect it with the window outlet.
You create IBOutlets by adding an instance variable to the class. If your app will only run on Leopard or higher, it's better to declare your outlets like this:
#interface FirstLaunch : NSWindowController {
NSTextField *myTextField;
}
#property (nonatomic, retain) IBOutlet NSTextField *myTextField;
#end
In Interface Builder, you'll control-drag a wire from the File's Owner onto the control to associate it with that outlet. Make sure that you release your reference to each IBOutlet in your class's dealloc method (if you're not using garbage collection) or else your app will leak memory.
Buttons send action messages when they're clicked, so you'll need to provide an action method for the button to call. You do that by declaring a method with a signature like this:
- (IBAction)myButtonClicked:(id)sender;
In Interface Builder, you'll control-drag a wire from the button onto your window controller and choose the myButtonClicked: method.
To make all this work, you'll need to create an instance of the window controller and tell it to load the NIB file at runtime. So, in your AppDelegate class, when you've determined that this is the first launch, you'll do this:
FirstLaunch *firstLaunchController = [[FirstLaunch alloc] initWithWindowNibName:#"nameOfNibFile"];
[firstLaunchController show:self];
You'll probably want to keep the reference to the window controller in an instance variable instead of a local variable like I've done here. And, depending on your application, it may make more sense to show this as a sheet. But once you've made it this far, you'll be able to figure out how to do that on your own.
Then, I'd like to be able to get mouse events for each button, so that I can do other things.
Don't worry about the mouse. There may not even be a mouse (think of the ever-popular tablet-Mac rumor).
I'd like to make a new class (FirstLaunch) for the first launch, but I'm not sure what to call from AppDelegate.
You make your own methods here. You'll probably make it a singleton*; then, you'll implement a method named something like runFirstLaunchPanel:, which will be an action method (more on those in a moment):
- (IBAction) runFirstLaunchPanel:(id)sender;
Instantiate the object in the nib, then, from your app delegate, call the action method with nil as the sender.
The reason to put the object in your nib and make the method an action method is that this makes it easy to hook up a menu item to it, so that the user can re-run the first-launch panel at a later time. (For example, if it's a Starting Points window, you might connect the New menu item to this action instead of the default one.)
*Yes, I've seen the articles about singletons, and I agree with them. In a case like this, it's OK.
Also, to get mouse events,
This is the wrong way of thinking about it. What you need to do is set your button up to send a message to your controller to make the controller (probably AppDelegate) do something. The message you want the button to send is an action message.
Implement an action method in the object that owns the nib containing the window with the buttons. Declare this method in the class's header, then connect the button to it in IB by right-clicking on your controller and dragging from the correct action method's circle to the button.
This is called the target-action paradigm, and it insulates controller responsibilities (doing things) from the views that ordered them. Because each action method does only one thing, you can have a button, a menu item, and even another controller (your app delegate, above) send the same action message, and the receiving controller won't have to care which control is sending the action, because it already knows what it has to do.
shouldn't I be a sublass of the buttons,
No. You very rarely create subclasses of anything other than NSObject (or, for model objects in Core Data, NSManagedObject) in Cocoa.
Note that I said “rarely”, not “never”. You will have to make the occasional subclass, especially if you want to create custom or customized views and cells (and, maybe, customized windows). However, subclassing is not necessary in Cocoa to the degree that (I hear) it is in some other frameworks on other platforms.
and considering that I have multiple buttons, I'm confused.
The target-action paradigm means you don't have to create one button subclass per button. One controller class implements all the actions, and the stock buttons, because you've hooked them up in IB, simply tell the controller “do this”.
Broken down, I need to access & manipulate IBOutlets I have set in IB,
Probably not. At least, not as much as you think you do.
determine when buttons are clicked (and which button was clicked).
Nope. The buttons will worry about being clicked; you just worry about setting them up to send, and then responding to, their action messages.