如何在任何地方等待脚本中的特定时间

Question

我正在尝试等待一段时间，但在加载页面之前会抛出异常。请告诉我如何在页面中显式等待。场景是 - 当主页加载时，加载器加载 5-6 秒。在这里我想等待加载器不禁用。

基类 ->

 package BasePOI;
import java.util.concurrent.TimeUnit;
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.firefox.FirefoxDriver;
public class Setup {
    public  static WebDriver driver;
    By counselor=By.id("counselor_login");
    public  void Websiteopen() 
    {
        driver = new FirefoxDriver();
        driver.manage().window().maximize();
        driver.manage().timeouts().implicitlyWait(20, TimeUnit.SECONDS);
        driver.get("url");
    }
    public Setup(WebDriver driver)
    {
        this.driver=driver;
    }
    public Setup()
    {
    }
    public WebDriver getDriver()
    {
        return this.driver;
    }
    public void click_Login_counselor()
    {
        driver.findElement(counselor).click();
    }
}

登录POI类--->

package BasePOI;
import java.util.concurrent.TimeUnit;
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;
public class LoginPOI {
    public WebDriver driver;
    // home
    By home_login = By.linkText("Login");
    By about_us = By.linkText("About Us");
    // login
    By counselor = By.id("counselor_login");
    By user = By.id("user_login");
    By username = By.id("username");
    By password = By.id("password");
    By Login = By.name("Login");
    By create_account = By.name("Login");
    By Logout = By.linkText("Logout");
    By Loader=By.id("loader");
    public void click_Login_button() {
        this.driver = new Setup().getDriver();
        //driver.manage().timeouts().pageLoadTimeout(10, TimeUnit.SECONDS);
        driver.findElement(home_login).click();
    }
    public void click_Login_counselor() {
        driver.findElement(counselor).click();
    }
    public void click_Login_user() {
        driver.findElement(user).click();
    }
    public void Enter_login_data(String uname, String pwd) {
        driver.findElement(username).clear();
        driver.findElement(username).sendKeys(uname);
        driver.findElement(password).clear();
        driver.findElement(password).sendKeys(pwd);
    }
    public void click_Login() {
        driver.findElement(Login).click();
    }
    public void waitforLogin(){
        System.out.println("a");
        WebDriverWait wait=new WebDriverWait(driver,15);
        WebElement b=wait.until(ExpectedConditions.visibilityOfElementLocated(Login));
        System.out.println(b);
    }
}

登录类-->

package Functionlity;
import org.openqa.selenium.WebDriver;
import org.testng.annotations.Test;
import BasePOI.LoginPOI;
import BasePOI.Setup;
public class Login  
{
    public WebDriver driver;
    @Test
    public void openwebsite() throws InterruptedException {
        Setup a = new Setup(driver);
        LoginPOI b = new LoginPOI();
        a.Websiteopen();
        b.waitforLogin();
        b.click_Login_button();

        b.click_Login_user();
        a.click_Login_counselor();
    }
}

错误--->

java.lang.NullPointerException
    at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:212)
    at org.openqa.selenium.support.ui.FluentWait.<init>(FluentWait.java:102)
    at org.openqa.selenium.support.ui.WebDriverWait.<init>(WebDriverWait.java:71)
    at org.openqa.selenium.support.ui.WebDriverWait.<init>(WebDriverWait.java:45)
    at BasePOI.LoginPOI.waitforLogin(LoginPOI.java:58)
    at Functionlity.Login.openwebsite(Login.java:20)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:86)
    at org.testng.internal.Invoker.invokeMethod(Invoker.java:643)
    at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:820)
    at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1128)
    at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:129)
    at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:112)
    at org.testng.TestRunner.privateRun(TestRunner.java:782)
    at org.testng.TestRunner.run(TestRunner.java:632)
    at org.testng.SuiteRunner.runTest(SuiteRunner.java:366)
    at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:361)
    at org.testng.SuiteRunner.privateRun(SuiteRunner.java:319)
    at org.testng.SuiteRunner.run(SuiteRunner.java:268)
    at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
    at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
    at org.testng.TestNG.runSuitesSequentially(TestNG.java:1244)
    at org.testng.TestNG.runSuitesLocally(TestNG.java:1169)
    at org.testng.TestNG.run(TestNG.java:1064)
    at org.testng.remote.RemoteTestNG.run(RemoteTestNG.java:113)
    at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:206)
    at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:177)

在执行点击登录按钮之前，我想等待页面加载器没有被禁用

Answer 1

尝试下面的代码，直到"pageloader"消失：

WebDriverWait wait = new WebDriverWait(driver, 10);
wait.until(ExpectedConditions.presenceOfElementLocated(By.id('loader')));
wait.until(ExpectedConditions.invisibilityOfElementLocated(By.id('loader')));