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Displaying Alerts in Xamarin.iOS

  • Artikkeli

Starting with iOS 8, UIAlertController has completed replaced UIActionSheet and UIAlertView both of which are now deprecated.

Unlike the classes it replaced, which are subclasses of UIView, UIAlertController is a subclass of UIViewController.

Use UIAlertControllerStyle to indicate the type of alert to display. These alerts types are:

  • UIAlertControllerStyleActionSheet
    • Pre-iOS 8 this would have been a UIActionSheet
  • UIAlertControllerStyleAlert
    • Pre-iOS 8 this would have been UIAlertView

There are three necessary steps to take when creating an Alert Controller:

  • Create and configure the Alert with a:

    • title
    • message
    • preferredStyle

  • (Optional) Add a text field

  • Add the Required actions

  • Present the View Controller

The simplest alert contains a single button, as shown in this screenshot:

Alert with one button

The code to display a simple alert is as follows:

okayButton.TouchUpInside += (sender, e) => {

    //Create Alert
    var okAlertController = UIAlertController.Create ("Title", "The message", UIAlertControllerStyle.Alert);

    //Add Action
    okAlertController.AddAction (UIAlertAction.Create ("OK", UIAlertActionStyle.Default, null));

    // Present Alert
    PresentViewController (okAlertController, true, null);
};

Displaying an alert with multiple options, is done in a similar fashion but add two actions. For example, the following screenshot shows an alert with two buttons:

Alert with two Buttons

okayCancelButton.TouchUpInside += ((sender, e) => {

    //Create Alert
    var okCancelAlertController = UIAlertController.Create("Alert Title", "Choose from two buttons", UIAlertControllerStyle.Alert);

    //Add Actions
    okCancelAlertController.AddAction(UIAlertAction.Create("OK", UIAlertActionStyle.Default, alert => Console.WriteLine ("Okay was clicked")));
    okCancelAlertController.AddAction(UIAlertAction.Create("Cancel", UIAlertActionStyle.Cancel, alert => Console.WriteLine ("Cancel was clicked")));

    //Present Alert
    PresentViewController(okCancelAlertController, true, null);
});

Alerts can also display an action sheet, similar to the screenshot below:

Action sheet alert

Buttons are added to the alert with the AddAction method:

actionSheetButton.TouchUpInside += ((sender, e) => {

    // Create a new Alert Controller
    UIAlertController actionSheetAlert = UIAlertController.Create("Action Sheet", "Select an item from below", UIAlertControllerStyle.ActionSheet);

    // Add Actions
    actionSheetAlert.AddAction(UIAlertAction.Create("OK",UIAlertActionStyle.Default, (action) => Console.WriteLine ("Item One pressed.")));

    actionSheetAlert.AddAction(UIAlertAction.Create("custom button 1",UIAlertActionStyle.Default, (action) => Console.WriteLine ("Item Two pressed.")));

    actionSheetAlert.AddAction(UIAlertAction.Create("Cancel",UIAlertActionStyle.Cancel, (action) => Console.WriteLine ("Cancel button pressed.")));

    // Required for iPad - You must specify a source for the Action Sheet since it is
    // displayed as a popover
    UIPopoverPresentationController presentationPopover = actionSheetAlert.PopoverPresentationController;
    if (presentationPopover!=null) {
        presentationPopover.SourceView = this.View;
        presentationPopover.PermittedArrowDirections = UIPopoverArrowDirection.Up;
    }

    // Display the alert
    this.PresentViewController(actionSheetAlert,true,null);
});