C# generics 用于在 Selenium+specflow 框架中链接页面对象

Question

I am trying to create a POM using Specflow and Selenium. I am following a course and he used C# generics to call pages. Can someone help me understand how this following code works:

class BasePage
{
    public T As<T>()where T: BasePage
    {
        return(T) this;
    }
}

---

public class PropertiesCollection
{
    private static BasePage _currentPage;
    
    public static BasePage currentPage
    {
        get{return _currentPage;}
        set{
            ScenarioContext.current["class"]=value;
            _currentPage=ScenarioContext.Current.Get<BasePage>("class");
           }
    }
}

---

code in step definition file:(instead of creating an object for every page and calling methods from it the code is written as follows)

[Then(@"I should be asked to enter Username and password")]
public void ThenIShouldBeAskedToEnterUsernameAndPassword()
{
    PropertiesCollection.currentPage.As<LoginPage>().Login(username,password);
}

---

The PropertiesCollection (above line of code) cannot read LoginPage until i create object (PropertiesCollection.currentPage = new LoginPage();) before the steps.

and also its not reading the next page

[Then(@"I should Login and see Welcome page")]
public void ThenIShouldLoginAndSeeWelcomePage()
{
PropertiesCollection.currentPage.As<WelcomePage>().WelcomeLabel();
}

its throwing an error: Unable to cast Login page to Welcome Page.

When i debug and check its(currentPage) is still in the LoginPage

Answer 1

I'll make an assumption about what the scenario looks like:

Scenario: Logging in
    When I log
    Then should be logged in and see the welcome page

The key here is setting up your page object model correctly. Methods that cause a new page to load should return the page model for that next page. When logging in, the LoginPage.Login(...) method should return an instance of WelcomePage. Your SpecFlow steps should call these page model methods and reassign the currentPage property whenever you expect the user to navigate to a new page.

Here is how to modify your LoginPage class:

public class LoginPage
{
    private readonly IWebDriver driver;

    public LoginPage(IWebDriver driver)
    {
        this.driver = driver;
    }

    ///
    /// <summary>
    /// Logs in and redirects to the welcome screen
    /// </summary>
    /// <param name="username"></param>
    /// <param name="password"></param>
    /// <returns>A page object model representing the welcome screen</returns>
    public WelcomePage Login(string username, string password)
    {
        // log in

        return new WelcomePage(driver);
    }
}

Notice that the Login() method does not just type the username and password into the form fields, then click the Log In button. It returns an instance of a page object that you expect the user to navigate to after successfully logging in.

Some example step definitions that set the currentPage property:

[When(@"I log in")]
public void WhenILogIn()
{
    // Initialize a new login page object
    var loginPage = new LoginPage(driver);

    // Log the user in, and assign reference to the next expected page
    // to a local variable.
    var welcomePage = loginPage.Login(username, password);

    // Set the "current page" the user should be on
    PropertiesCollection.currentPage = welcomePage;
}

[Then(@"should be logged in and see welcome page")]
public void ThenShouldBeLoggedInAndSeeWelcomePage()
{
    // Get the "current page" and cast it to the expected type:
    var welcomePage = PropertiesCollection.currentPage.As<WelcomePage>();

    // Make your assertion:
    Assert.AreEqual("Welcome!", welcomePage.WelcomeLabel());
}