問題描述

當我嘗試在頁面對象中使用靜態方法時，我遇到了 NullPointerExceptions 問題.如果我使用非靜態方法，它工作正常.

I'm having trouble with NullPointerExceptions when I try using static methods in a page object. If I do it with non-static methods, it works fine.

非靜態版本:

public class ComplaintPage {

    private ExtendedWebDriver driver;

    @FindBy(css = "[data-selector=date-received-complaint]")
    public WebElement dateComplaintReceoved;

    public ComplaintPage() {
        driver = Browser.extendedDriver();
        PageFactory.initElements(driver, this);
    }

    public void setComplaintDate() {
        dateComplaintReceoved.sendKeys(LocalDate.now().toString());
    }
}

Calling code:

ComplaintPage complaintPage = new ComplaintPage;
complaintPage.setComplaintDate();

這很好用.日期字段已設置.

This works fine. The date field is set.

靜態版

public class ComplaintPage {

    private static ExtendedWebDriver driver;

    @FindBy(css = "[data-selector=date-received-complaint]")
    public static WebElement dateComplaintReceoved;

    public ComplaintPage() {
        driver = Browser.extendedDriver();
        PageFactory.initElements(driver, this);
    }

    public void static setComplaintDate() {
*       dateComplaintReceoved.sendKeys(LocalDate.now().toString());
    }
}

Calling code:

ComplaintPage.setComplaintDate();

這不起作用，并在標有*"的行(訪問 WebElement 的行)上導致 java.lang.NullPointerException.

This does not work, and results in a java.lang.NullPointerException on the line marked with "*" (the line accessing the WebElement).

我有點喜歡在測試中使用像這樣的靜態方法，因為我真的看不出它有什么問題，而且它使代碼更易于閱讀.我以前在 C#/VS 中做過，但由于某種原因，我在這里遺漏了一些重要的東西.

I kind of like using static methods like this in test, since I don't really see a problem with it, and it makes the code even more easy to read. And I've done it before, in C#/VS, but for some reason I'm missing something important here.

推薦答案

NullPointerException 因為 PageFactory 的工作方式而被拋出.你看，當你創建一個 ComplaintPage 類的實例時，你正在調用它的構造函數:

NullPointerException is thrown because of how PageFactory works. You see, when you create an instance of ComplaintPage class, you are invoking its constructor:

public ComplaintPage() {
        driver = Browser.extendedDriver();
        PageFactory.initElements(driver, this);
    }

構造函數調用PageFactory類的initElements方法.此方法使用 Java 反射 API 初始化所有 WebElement 和 List> 字段.它基本上將默認的 null 值更改為接口的實現.它還提供了一種 WebElement 的惰性實例化，這意味著 - WebElement 僅在需要時才被發現(尋找?) - 當您調用它們的操作時.

    public void static setComplaintDate(WebDriver driver) {
        driver.findElement(By.cssSelector("[data-selector=date-received-complaint]")).sendKeys(LocalDate.now().toString());
    }