Jake Ginnivan’s blog

Retry.For

With UI automation, you are constantly dealing with race conditions, especially in a good WPF app which lazy loads most things, and while we have put a lot of good helpers in place (WaitWhileBusy etc), there are still times where a button does not enable quick enough, or a windows is opening and if you do not have automatic retry enabled you will have quite fragile UI automation tests.

This is where my Retry static class comes in handy.

Usage

var element = Retry.ForDefault(
                  () => screen.WhiteWindow.Get(searchCriteria),
                  b => (bool)b.AutomationElement.GetCurrentPropertyValue(AutomationElement.IsOffscreenProperty, false));

or for retrying if a locked log file is encountered (app still shutting down, or in middle of a write)

Retry.For(() => File.Exists(@"C:\Logs\Terminal.log"), 5)

It will automatically retry if a value type is default, i.e if you call

Retry.For<int>(()=>default(int), 5); //Will retry for 5 seconds, then return default(int)

And some more of the default conditions that cause retry

  • Exception thrown
  • Value type == default(type)
  • Reference type == null
  • bool == false

You can also override the default conditions with a predicate.

Code

public static class Retry { public const int WindowWaitDefault = 30; public const int ElementWaitDefault = 10;

    public static Window ForDefault(Func<Window> getMethod)
    {
        return For(getMethod, WindowWaitDefault);
    }

    public static T ForDefault<T>(Func<T> getMethod)
    {
        return For(getMethod, ElementWaitDefault);
    }

    public static Window ForDefault(Func<Window> getMethod, Predicate<Window> shouldRetry)
    {
        return For(getMethod, shouldRetry, WindowWaitDefault);
    }

    public static T ForDefault<T>(Func<T> getMethod, Predicate<T> shouldRetry)
    {
        return For(getMethod, shouldRetry, ElementWaitDefault);
    }

    /// <summary>
    /// Retrys until action does not throw an exception
    /// </summary>
    /// <param name="action">The action.</param>
    /// <param name="retryForSeconds">The retry for seconds.</param>
    public static void For(Action action, int retryForSeconds)
    {
        var startTime = DateTime.Now;
        while (DateTime.Now.Subtract(startTime).TotalSeconds < retryForSeconds)
        {
            try
            {
                action();
                return;
            }
            catch (Exception)
            {
                Thread.Sleep(500);
                continue;
            }
        }

        action();
    }

    public static bool For(Func<bool> getMethod, int retryForSeconds)
    {
        return For(getMethod, g => !g, retryForSeconds);
    }

    public static T For<T>(Func<T> getMethod, int retryForSeconds)
    {
        //If T is a value type, by default we should retry if the value is default
        //Reference types will return fase, so our predecate will always pass
        return For(getMethod, IsValueTypeAndDefault, retryForSeconds);
    }

    public static T For<T>(Func<T> getMethod, Predicate<T> shouldRetry, int retryForSeconds)
    {
        var startTime = DateTime.Now;
        T element;
        while (DateTime.Now.Subtract(startTime).TotalSeconds < retryForSeconds)
        {
            try
            {
                element = getMethod();
            }
            catch (Exception)
            {
                Thread.Sleep(500);
                continue;
            }

            //Making it safe for bool and value types and reference types
            if (typeof(T) == typeof(bool) && !shouldRetry(element))
                return element;

            if (typeof(T) != typeof(bool) &&
                !IsReferenceTypeAndIsNull(element) &&
                !shouldRetry(element))
            {
                return element;
            }

            Thread.Sleep(500);
        }

        element = getMethod();
        return element;
    }

    private static bool IsReferenceTypeAndIsNull<T>(T element)
    {
        return (!(typeof(T).IsValueType) && ReferenceEquals(element, null));
    }

    private static bool IsValueTypeAndDefault<T>(T element)
    {
        return (typeof(T).IsValueType && element.Equals(default(T)));
    }
}

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