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UITest - making setting iOS pickers easier with backdoors.

JamesLaveryJamesLavery GBBeta, University ✭✭✭✭✭

I've found that setting Pickers on iOS is difficult via UITest - to get round this I've written some iOS Backdoors which make the process much easier - see the UITest-Pickers repo.

For details, is reproduced below.

Any comments/suggestions for improvements welcome.



Driving iOS Pickers from UITest tests is painful - usually we end up coding gestures and scroll commands. All nasty and error-prone.

To get round this, I've created a set of Backdoor methods which can be called from UITest tests to directly select Picker values.

Supported Pickers are:

  • Ordinary Pickers with a list of items
  • Date Pickers.

Note that these backdoors and supporting classes are only for iOS.



  1. Add UITestBackdoorMethods.cs to your iOS project.
  2. Amend AppDelegate.cs to add the actual backdoor methods which will be Invoked.

Invoking The Backdoors

The Backdoors can be invoked via extension methods defined for the UITest App class:

// Set an ordinary picker to index 2, showing the picker as it's set
AppManager.App.SetFormsPickerIndex(AppManager.Platform, "MyPickerAutomationId", "2", true);
// Set an ordinary picker to the value "Second item", without showing the picker as it's set
AppManager.App.SetFormsPickerIndex(AppManager.Platform, "MyPickerAutomationId", "Second item", false);
// set a date picker, showing the Picker at it's updated
AppManager.App.SetFormsDatePickerValue(AppManager.Platform, "MyDatePickerAutomationId", dateValue , true);

Note that AppManager above is an artefact of the UITest project setup (see below).

Ancillary Architecture

The repo has other artefacts which are not directly concerned with the backdoors themselves, but make UITest management and debugging easier.

MVVM Framework

The test app makes use of FreshMvvm for its MVVM implementation.

UITestPickerBackdoors.UITests Project

This implements the Page Object Pattern and other concepts presented in this Xamarin Blog - Best Practices and Tips for Using Xamarin.UITest

The Backdoors are invoked using extensions to the UITest App object, defined in AppPickerExtensions.cs.

In addition, I use a wrapper UIElement class, which allows us to access either the underlying UI View or the AutomationId for the View. I've found this useful because we need to know the AutomationId and View for a visual element - for example, scrolling takes an AutomationId in some cases and the Element in others.

Allowing Debugging Of Backdoors

Out of the box, it's not easy to debug a Backdoor, because when you're running the UITest, you can only debug the UITest project itself - the Backdoor is being Invoked.

To get round this, I've created an IBackdoorRunner interface, which is implemented in the iOS project. This allows us run the app and run the underlying Backdoor code from the app itself.

Obviously, this Interface and its implementation are not needed in a project which makes use of the Backdoors - but is useful when developing and debugging them.

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