How can you add a UIGestureRecognizer to a UIBarBu

Question

Problem

In my iPad app, I cannot attach a popover to a button bar item only after press-and-hold events. But this seems to be standard for undo/redo. How do other apps do this?

Background

I have an undo button (UIBarButtonSystemItemUndo) in the toolbar of my UIKit (iPad) app. When I press the undo button, it fires it's action which is undo:, and that executes correctly.

However, the "standard UE convention" for undo/redo on iPad is that pressing undo executes an undo but pressing and holding the button reveals a popover controller where the user selected either "undo" or "redo" until the controller is dismissed.

The normal way to attach a popover controller is with presentPopoverFromBarButtonItem:, and I can configure this easily enough. To get this to show only after press-and-hold we have to set a view to respond to "long press" gesture events as in this snippet:

UILongPressGestureRecognizer *longPressOnUndoGesture = [[UILongPressGestureRecognizer alloc] 
       initWithTarget:self 
               action:@selector(handleLongPressOnUndoGesture:)];
//Broken because there is no customView in a UIBarButtonSystemItemUndo item
[self.undoButtonItem.customView addGestureRecognizer:longPressOnUndoGesture];
[longPressOnUndoGesture release];

With this, after a press-and-hold on the view the method handleLongPressOnUndoGesture: will get called, and within this method I will configure and display the popover for undo/redo. So far, so good.

The problem with this is that there is no view to attach to. self.undoButtonItem is a UIButtonBarItem, not a view.

Possible solutions

1) [The ideal] Attach the gesture recognizer to the button bar item. It is possible to attach a gesture recognizer to a view, but UIButtonBarItem is not a view. It does have a property for .customView, but that property is nil when the buttonbaritem is a standard system type (in this case it is).

2) Use another view. I could use the UIToolbar but that would require some weird hit-testing and be an all around hack, if even possible in the first place. There is no other alternative view to use that I can think of.

3) Use the customView property. Standard types like UIBarButtonSystemItemUndo have no customView (it is nil). Setting the customView will erase the standard contents which it needs to have. This would amount to re-implementing all the look and function of UIBarButtonSystemItemUndo, again if even possible to do.

Question

How can I attach a gesture recognizer to this "button"? More specifically, how can I implement the standard press-and-hold-to-show-redo-popover in an iPad app?

Ideas? Thank you very much, especially if someone actually has this working in their app (I'm thinking of you, omni) and wants to share...

Answer 1

Note: this no longer works as of iOS 11

In lieu of that mess with trying to find the UIBarButtonItem's view in the toolbar's subview list, you can also try this, once the item is added to the toolbar:

[barButtonItem valueForKey:@"view"];

This uses the Key-Value Coding framework to access the UIBarButtonItem's private _view variable, where it keeps the view it created.

Granted, I don't know where this falls in terms of Apple's private API thing (this is public method used to access a private variable of a public class - not like accessing private frameworks to make fancy Apple-only effects or anything), but it does work, and rather painlessly.

Answer 2

I tried @voi1d's solution, which worked great until I changed the title of the button that I had added a long press gesture to. Changing the title appears to create a new UIView for the button that replaces the original, thus causing the added gesture to stop working as soon as a change is made to the button (which happens frequently in my app).

My solution was to subclass UIToolbar and override the addSubview: method. I also created a property that holds the pointer to the target of my gesture. Here's the exact code:

- (void)addSubview:(UIView *)view {
    // This method is overridden in order to add a long-press gesture recognizer
    // to a UIBarButtonItem. Apple makes this way too difficult, but I am clever!
    [super addSubview:view];
    // NOTE - this depends the button of interest being 150 pixels across (I know...)
    if (view.frame.size.width == 150) {
        UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:targetOfGestureRecognizers 
                                                                                                action:@selector(showChapterMenu:)];
        [view addGestureRecognizer:longPress];
    }
}

In my particular situation, the button I'm interested in is 150 pixels across (and it's the only button that is), so that's the test I use. It's probably not the safest test, but it works for me. Obviously you'd have to come up with your own test and supply your own gesture and selector.

The benefit of doing it this way is that any time my UIBarButtonItem changes (and thus creates a new view), my custom gesture gets attached, so it always works!

Answer 3

This is an old question, but it still comes up in google searches, and all of the other answers are overly complicated.

I have a buttonbar, with buttonbar items, that call an action:forEvent: method when pressed.

In that method, add these lines:

bool longpress=NO;
UITouch *touch=[[[event allTouches] allObjects] objectAtIndex:0];
if(touch.tapCount==0) longpress=YES;

If it was a single tap, tapCount is one. If it was a double tap, tapCount is two. If it's a long press, tapCount is zero.

Answer 4

I tried something similar to what Ben suggested. I created a custom view with a UIButton and used that as the customView for the UIBarButtonItem. There were a couple of things I didn't like about this approach:

• The button needed to be styled to not stick out like a sore thumb on the UIToolBar
• With a UILongPressGestureRecognizer I didn't seem to get the click event for "Touch up Inside" (This could/is most likely be programing error on my part.)

Instead I settled for something hackish at best but it works for me. I'm used XCode 4.2 and I'm using ARC in the code below. I created a new UIViewController subclass called CustomBarButtonItemView. In the CustomBarButtonItemView.xib file I created a UIToolBar and added a single UIBarButtonItem to the toolbar. I then shrunk the toolbar to almost the width of the button. I then connected the File's Owner view property to the UIToolBar.

Then in my ViewController's viewDidLoad: message I created two UIGestureRecognizers. The first was a UILongPressGestureRecognizer for the click-and-hold and second was UITapGestureRecognizer. I can't seem to properly get the action for the UIBarButtonItem in the view so I fake it with the UITapGestureRecognizer. The UIBarButtonItem does show itself as being clicked and the UITapGestureRecognizer takes care of the action just as if the action and target for the UIBarButtonItem was set.

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

    UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(longPressGestured)];

    UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(buttonPressed:)];

    CustomBarButtomItemView* customBarButtonViewController = [[CustomBarButtomItemView alloc] initWithNibName:@"CustomBarButtonItemView" bundle:nil];

    self.barButtonItem.customView = customBarButtonViewController.view;

    longPress.minimumPressDuration = 1.0;

    [self.barButtonItem.customView addGestureRecognizer:longPress];
    [self.barButtonItem.customView addGestureRecognizer:singleTap];        

}

-(IBAction)buttonPressed:(id)sender{
    NSLog(@"Button Pressed");
};
-(void)longPressGestured{
    NSLog(@"Long Press Gestured");
}

Now when a single click occurs in the ViewController's barButtonItem (Connected via the xib file) the tap gesture calls the buttonPressed: message. If the button is held down longPressGestured is fired.

For changing the appearance of the UIBarButton I'd suggest making a property for CustomBarButtonItemView to allow access to the Custom BarButton and store it in the ViewController class. When the longPressGestured message is sent you can change the system icon of the button.

One gotcha I've found is the customview property takes the view as is. If you alter the custom UIBarButtonitem from the CustomBarButtonItemView.xib to change the label to @"really long string" for example the button will resize itself but only the left most part of the button shown is in the view being watched by the UIGestuerRecognizer instances.

Answer 5

While this question is now over a year old, this is still a pretty annoying problem. I've submitted a bug report to Apple (rdar://9982911) and I suggest that anybody else who feels the same duplicate it.

Answer 6

Option 1 is indeed possible. Unfortunately it's a painful thing to find the UIView that the UIBarButtonItem creates. Here's how I found it:

[[[myToolbar subviews] objectAtIndex:[[myToolbar items] indexOfObject:myBarButton]] addGestureRecognizer:myGesture];

This is more difficult than it ought to be, but this is clearly designed to stop people from fooling around with the buttons look and feel.

Note that Fixed/Flexible spaces are not counted as views!

In order to handle spaces you must have some way of detecting them, and sadly the SDK simply has no easy way to do this. There are solutions and here are a few of them:

1) Set the UIBarButtonItem's tag value to it's index from left to right on the toolbar. This requires too much manual work to keep it in sync IMO.

2) Set any spaces' enabled property to NO. Then use this code snippet to set the tag values for you:

NSUInteger index = 0;
for (UIBarButtonItem *anItem in [myToolbar items]) {
    if (anItem.enabled) {
        // For enabled items set a tag.
        anItem.tag = index;
        index ++;
    }
}

// Tag is now equal to subview index.
[[[myToolbar subviews] objectAtIndex:myButton.tag] addGestureRecognizer:myGesture];

Of course this has a potential pitfall if you disable a button for some other reason.

3) Manually code the toolbar and handle the indexes yourself. As you'll be building the UIBarButtonItem's yourself, so you'll know in advance what index they'll be in the subviews. You could extend this idea to collecting up the UIView's in advance for later use, if necessary.