When working with a UIViewController one of the most used pieces of functionality is dismissing the view
controller. As more and more projects where created and more and more UIViewController classes were created
it was noticed that the same piece of code was continually being written over and over again.
Dismiss Modal View Controller Code
- (IBAction)dismiss:(id)sender
{
[self dismissViewControllerAnimated:YES];
}
The IBAction from the above code will allow the user to attach an event from the Interface Builder to this
method and dismiss the currently displayed UIViewController. Since animated is YES it will
perform a default iOS animation unless you have overridden the animation in your UIViewController delegate.
It was therefore determined that a category could be created on the UIViewController object that would have
this code already pre-written and hence you would only ever have to include the category in your project and
the functionality would be there in one place. This category would be very simple incorporating the code
written above along with two other useful category methods. The full category is shown below.
@implementation UIViewController (DTFDismiss)
- (IBAction)dtf_dismissViewController:(id)sender
{
[self dismissViewControllerAnimated:YES completion:nil];
}
- (IBAction)dtf_popViewController:(id)sender
{
[self.navigationController popViewControllerAnimated:YES];
}
- (IBAction)dtf_popToRootViewController:(id)sender
{
[self.navigationController popToRootViewControllerAnimated:YES];
}
@end
The two extra category methods associated with the UIViewController are based on using a UINavigationController
with the functionality and pop the current view off the UINavigationController stack or alternatively the
second option will pop all of the view controllers off the UINavigationController stack and return you to
the root view controller for the UINavigationController.
Controlling the Animated Portion
From the above code snipet you only have the ability to set the animation value while dismissing the view controller to YES.
From a developer perspective this is a limitation since the methods would have to be duplicated with the appropriate NO or YES
values for each animation depending which is not what we want to achieve in any helper methods being created.
Since the main aspect of this library is to allow you to utilize the Storyboard it would be better if the
library also allowed you to control the animation property from the Storyboard. Initially for this it was
assumed you could just put a property in the Storyboard key/value pairs for the object and this would allow
you to have access to what the user wished.
Putting the above key path into the Storyboard file as shown above will cause the application to crash when the view controller / specifically the button is unarchived from the Storyboard file. The reason for this is the property does not exist on the button and hence when it is set the button does not respond to the selector and the application crashes. In order to get around this issue we need to create a category on the objects that we wish this functionality from the Storyboard upon. In this case it was determined to put the category on NSObject since this covers all of the necessary objects because UIBarButtonItem does not inherit from UIView so NSObject is the first in both UIButton and UIBarButtonItem hierarchies that matches both of the items most likely to utilize this functionality.
The NSObject+DTFDismissAnimate category utilizes the Objective C runtime in order to allow creation of a new
property on a class without subclassing the class. Using the Objective C runtime objc_setAssociatedObject
and objc_getAssociated methods we can simulate the NSObject class having the new runtime property
dtfDismissAnimate. As seen below the category is using the NSNumber class to store the value. This
behavior was required because we cannot associate anything which is not an object and NSNumber allows the application
to store BOOLEAN values and retrieve the values where requested.
@interface NSObject (DTFDismissAnimate)
@property (nonatomic, assign) BOOL dtfDismissAnimate;
@end
#import <objc/runtime.h>
static const void *kDTFDismissAnimateKey = &kDTFDismissAnimateKey;
@implementation NSObject (DTFDismissAnimate)
- (void)setDtfDismissAnimate:(BOOL)dtfDismissAnimate
{
objc_setAssociatedObject(self, kDTFDismissAnimateKey, @(dtfDismissAnimate), OBJC_ASSOCIATION_RETAIN);
}
- (BOOL)dtfDismissAnimate
{
NSNumber *associated = objc_getAssociatedObject(self, kDTFDismissAnimateKey);
return associated ? [associated boolValue] : NO;
}
@end
As can be seen the header file just declares the property dtfDismissAnimate as a BOOL property. This
property will be used as any other property on an object for holding the value of the animation. In the implementation
of the category we declare a static constant key that shall hold the value of the property on the object. We
have to implement the getter and setter manually since Objective C will not synthesize them for us. The getter is just a
simple lookup on the object for the value associated with the kDTFDismissAnimateKey. If a value exists
it will be returned otherwise a default of NO is returned since we cannot return nil when the return
type is not an object. Now we have the category defined running the application and loading the view controller
containing the button with our dtfDismissAnimate key path will no longer crash the application but allow
the UIViewController category to retrieve the value from the user defined Storyboard value and either animate or
not animate the transition of dismissing the view controller.
Storyboard Setup
Once you have all of the files setup in your project, you can now utilize the storyboard to setup dismissing the
modal view controller. Dragging from the UIBarButtonItem in the case below to the UIViewController will popup the
choices and inside the actions choices you will see the three choices made available by the category. Choosing the
dtf_dismissViewController method will allow the application to dismiss the view controller and if
you set the animation property as shown above then this will determine whether the view controller is dismissed with
an animation or not.
Conclusion
This category is useful to avoid code duplication across multiple view controllers. The ability to set the animation property also provides the user with the advantage of being able to configure everything through the Storyboard without having to go into the code base itself and change properties or add any additional code. The category code for this blog can be found here. A brief sample project with a dismissable modal view controller can be found here.
UIView Hierarchy