Custom View in UIAlertController

问题:

I am trying to put a custom view inside a UIAlertController. I'm running into some odd issues with the sizing of the custom view.

I want the custom view to span the width of the UIAlertController, whatever that might be. I'm using CGRectGetWidth(alertController.view.bounds) to get the width of the alert controller. However, this seems instead to be returning the width of the entire view. using view.frame does not make a difference.

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"My Title" message:nil preferredStyle:UIAlertControllerStyleAlert];

UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, CGRectGetWidth(alertController.view.bounds), 50)];
view.backgroundColor = [UIColor blueColor];

[alertController.view addSubview:view];
[self presentViewController:alertController animated:YES completion:nil];

This yields the results below. I have the same issue trying to get X, Y width and height properties of the UIAlertController. Does anyone know how I can position this view in the middle of the alert controller without using hard-coded numbers?

回答1:

You're not supposed to do that. To quote the docs:

The UIAlertController class is intended to be used as-is and does not support subclassing.

The view hierarchy for this class is private and must not be modified.

If you go against an explicit statement like that from Apple all bets are off, and even if you can get it to work on the current OS version, it could break with any future version.

回答2:

Here's an alternative.It's not adding subview to UIAlertControl's view hierarchy, but to UIWindow instead in appropriate position. To track UIAlertControl's view frame the view controller is extended with a custom .view getter using obj-c runtime/swift extension which calls UIViewController super class implementation. This allows avoiding genuine view's private class dependence and is neither subclassing UIAlertControl or modifying it's view hierarchy.

Example screenshot

Objective-C

#import <objc/runtime.h>
#import <objc/message.h>
@implementation AppDelegate
+ (UIView*)alertHelperView
{
    static UIView *alertHelperView = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        alertHelperView = [UIView new];
        alertHelperView.backgroundColor = [UIColor redColor];
        alertHelperView.frame = CGRectZero;
    });
    return alertHelperView;
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    [self.window addSubview:[AppDelegate alertHelperView]];
    return YES;
}
@end
@implementation ViewController

- (void)viewDidAppear:(BOOL)animated {
    Class class = [UIAlertController class];
    class_addMethod(class, @selector(view), imp_implementationWithBlock(^(__unsafe_unretained UIAlertController* self) {

        struct objc_super super = {
            .receiver = self,
            .super_class = class_getSuperclass(class)
        };

        id (*objc_msgSendSuper_typed)(struct objc_super *, SEL) = (void *)&objc_msgSendSuper;

        UIView* myView = objc_msgSendSuper_typed(&super, @selector(view));
        CGRect newFrame = myView.frame;
        if (!self.isBeingPresented) {
            [AppDelegate alertHelperView].frame = CGRectZero;
        } else {
            [[AppDelegate alertHelperView].superview bringSubviewToFront:[AppDelegate alertHelperView]];
            [AppDelegate alertHelperView].frame = CGRectMake(newFrame.origin.x,
                                                             newFrame.origin.y,
                                                             newFrame.size.width/2,
                                                             newFrame.size.height/2);
        }
        return myView;
    }), "@@:");

    UIAlertController * alert=   [UIAlertController
                                  alertControllerWithTitle:@"Info"
                                  message:@"You are using UIAlertController"
                                  preferredStyle:UIAlertControllerStyleAlert];

    UIAlertAction* ok = [UIAlertAction
                         actionWithTitle:@"OK"
                         style:UIAlertActionStyleDefault
                         handler:^(UIAlertAction * action)
                         {
                         }];
    UIAlertAction* cancel = [UIAlertAction
                             actionWithTitle:@"Cancel"
                             style:UIAlertActionStyleDefault
                             handler:^(UIAlertAction * action)
                             {
                             }];

    [alert addAction:ok];
    [alert addAction:cancel];

    [self presentViewController:alert animated:YES completion:nil];
}
@end

Swift 3.1

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
        static var alertHelperView : UIView!

        func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
            AppDelegate.alertHelperView = UIView()
            AppDelegate.alertHelperView.backgroundColor = .red
            self.window?.addSubview(AppDelegate.alertHelperView!)
            return true
        }
  }

    extension UIAlertController {
        open override var view: UIView! {
            get {
                let newFrame : CGRect = super.view.frame
                if !self.isBeingPresented {
                    AppDelegate.alertHelperView.frame = CGRect.zero
                } else {
                    AppDelegate.alertHelperView.superview?.bringSubview(toFront: AppDelegate.alertHelperView)
                    AppDelegate.alertHelperView.frame = CGRect(x:newFrame.origin.x,y:newFrame.origin.y,width:newFrame.size.width/2,height:newFrame.size.height/2)
                }
                return super.view
            }
            set(newValue) {
                super.view = newValue
            }
        }
    }

    class ViewController: UIViewController {
        override func viewDidAppear(_ animated: Bool) {
            let alertController = UIAlertController(title: "Default Style", message: "A standard alert.", preferredStyle: .alert)

            let cancelAction = UIAlertAction(title: "Cancel", style: .cancel) { action in
                // ...
            }
            alertController.addAction(cancelAction)

            let OKAction = UIAlertAction(title: "OK", style: .default) { action in
                // ...
            }
            alertController.addAction(OKAction)
            self.present(alertController, animated: false) {
            }
        }
    }
}