EDIT: These problems appear to be fixed as of iOS 7.1 / Xcode 5.1.1. (Possibly earlier, as I haven't been able to test all versions. Definitely after iOS 7.0, since I tested that one.) When you create a popover segue from a UIBarButtonItem, the segue makes sure that tapping the popover again hides the popover rather than showing a duplicate. It works right for the new UIPresentationController-based popover segues that Xcode 6 creates for iOS 8, too.

Since my solution may be of historical interest to those still supporting earlier iOS versions, I've left it below.

If you store a reference to the segue's popover controller, dismissing it before setting it to a new value on repeat invocations of prepareForSegue:sender:, all you avoid is the problem of getting multiple stacking popovers on repeated presses of the button -- you still can't use the button to dismiss the popover as the HIG recommends (and as seen in Apple's apps, etc.)

You can take advantage of ARC zeroing weak references for a simple solution, though:

1: Segue from the button

As of iOS 5, you couldn't make this work with a segue from a UIBarButtonItem, but you can on iOS 6 and later. (On iOS 5, you'd have to segue from the view controller itself, then have the button's action call performSegueWithIdentifier: after checking for the popover.)

2: Use a reference to the popover in -shouldPerformSegue...

@interface ViewController
@property (weak) UIPopoverController *myPopover;
@end

@implementation ViewController
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // if you have multiple segues, check segue.identifier
    self.myPopover = [(UIStoryboardPopoverSegue *)segue popoverController];
}
- (BOOL)shouldPerformSegueWithIdentifier:(NSString *)identifier sender:(id)sender {
    if (self.myPopover) {
        [self.myPopover dismissPopoverAnimated:YES];
        return NO;
    } else {
        return YES;
    }
}
@end

3: There's no step three!

The nice thing about using a zeroing weak reference here is that once the popover controller is dismissed -- whether programmatically in shouldPerformSegueWithIdentifier:, or automatically by the user tapping somewhere else outside the popover -- the ivar goes to nil again, so we're back to our initial state.

Without zeroing weak references, we'd have to also:

• set myPopover = nil when dismissing it in shouldPerformSegueWithIdentifier:, and
• set ourself as the popover controller's delegate in order to catch popoverControllerDidDismissPopover: and also set myPopover = nil there (so we catch when the popover is automatically dismissed).

Using Objective-C Classes in Swift

If you have an existing class that you'd like to use, perform Step 2 and then skip to Step 5. (For some cases, I had to add an explicit #import <Foundation/Foundation.h to an older Objective-C File.)

Step 1: Add Objective-C Implementation -- .m

Add a .m file to your class, and name it CustomObject.m.

Step 2: Add Bridging Header

When adding your .m file, you'll likely be hit with a prompt that looks like this:

Click Yes!

If you did not see the prompt, or accidentally deleted your bridging header, add a new .h file to your project and name it <#YourProjectName#>-Bridging-Header.h.

In some situations, particularly when working with Objective-C frameworks, you don't add an Objective-C class explicitly and Xcode can't find the linker. In this case, create your .h file named as mentioned above, then make sure you link its path in your target's project settings like so:

Note:

It's best practice to link your project using the $(SRCROOT) macro so that if you move your project, or work on it with others using a remote repository, it will still work. $(SRCROOT) can be thought of as the directory that contains your .xcodeproj file. It might look like this:

$(SRCROOT)/Folder/Folder/<#YourProjectName#>-Bridging-Header.h

Step 3: Add Objective-C Header -- .h

Add another .h file and name it CustomObject.h.

Step 4: Build your Objective-C Class

In CustomObject.h

#import <Foundation/Foundation.h>

@interface CustomObject : NSObject

@property (strong, nonatomic) id someProperty;

- (void) someMethod;

@end

In CustomObject.m

#import "CustomObject.h"

@implementation CustomObject 

- (void) someMethod {
    NSLog(@"SomeMethod Ran");
}

@end

Step 5: Add Class to Bridging-Header

In YourProject-Bridging-Header.h:

#import "CustomObject.h"

Step 6: Use your Object

In SomeSwiftFile.swift:

var instanceOfCustomObject = CustomObject()
instanceOfCustomObject.someProperty = "Hello World"
print(instanceOfCustomObject.someProperty)
instanceOfCustomObject.someMethod()

There is no need to import explicitly; that's what the bridging header is for.

Using Swift Classes in Objective-C

Step 1: Create New Swift Class

Add a .swift file to your project, and name it MySwiftObject.swift.

In MySwiftObject.swift:

import Foundation

@objc(MySwiftObject)
class MySwiftObject : NSObject {

    @objc
    var someProperty: AnyObject = "Some Initializer Val" as NSString

    init() {}

    @objc
    func someFunction(someArg: Any) -> NSString {
        return "You sent me \(someArg)"
    }
}

Step 2: Import Swift Files to ObjC Class

In SomeRandomClass.m:

#import "<#YourProjectName#>-Swift.h"

The file:<#YourProjectName#>-Swift.h should already be created automatically in your project, even if you can not see it.

Step 3: Use your class

MySwiftObject * myOb = [MySwiftObject new];
NSLog(@"MyOb.someProperty: %@", myOb.someProperty);
myOb.someProperty = @"Hello World";
NSLog(@"MyOb.someProperty: %@", myOb.someProperty);

NSString * retString = [myOb someFunctionWithSomeArg:@"Arg"];

NSLog(@"RetString: %@", retString);

Notes:

1. If Code Completion isn't behaving as you expect, try running a quick build with ⌘⇧R to help Xcode find some of the Objective-C code from a Swift context and vice versa.

2. If you add a .swift file to an older project and get the error dyld: Library not loaded: @rpath/libswift_stdlib_core.dylib, try completely restarting Xcode.

3. While it was originally possible to use pure Swift classes (Not descendents of NSObject) which are visible to Objective-C by using the @objc prefix, this is no longer possible. Now, to be visible in Objective-C, the Swift object must either be a class conforming to NSObjectProtocol (easiest way to do this is to inherit from NSObject), or to be an enum marked @objc with a raw value of some integer type like Int. You may view the edit history for an example of Swift 1.x code using @objc without these restrictions.