问题描述

当我尝试在页面对象中使用静态方法时，我遇到了 NullPointerExceptions 问题.如果我使用非静态方法，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.

非静态版本:

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();

这很好用.日期字段已设置.

This works fine. The date field is set.

静态版

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();

这不起作用，并在标有*"的行(访问 WebElement 的行)上导致 java.lang.NullPointerException.

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

我有点喜欢在测试中使用像这样的静态方法，因为我真的看不出它有什么问题，而且它使代码更易于阅读.我以前在 C#/VS 中做过，但由于某种原因，我在这里遗漏了一些重要的东西.

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.

推荐答案

NullPointerException 因为 PageFactory 的工作方式而被抛出.你看，当你创建一个 ComplaintPage 类的实例时，你正在调用它的构造函数:

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);
    }

构造函数调用PageFactory类的initElements方法.此方法使用 Java 反射 API 初始化所有 WebElement 和 List> 字段.它基本上将默认的 null 值更改为接口的实现.它还提供了一种 WebElement 的惰性实例化，这意味着 - WebElement 仅在需要时才被发现(寻找?) - 当您调用它们的操作时.

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