如何在Wait.until()中使用selenium 2 PageFactory init元素？

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.FindBy;
import org.openqa.selenium.support.PageFactory;
import org.openqa.selenium.support.ui.WebDriverWait;
import org.openqa.selenium.support.ui.ExpectedConditions;

public class LoginPage {
    private WebDriver driver;
    private WebDriverWait wait;

    @FindBy(id = "username")
    private WebElement usernameInput;

    @FindBy(id = "password")
    private WebElement passwordInput;

    @FindBy(id = "login-button")
    private WebElement loginButton;

    public LoginPage(WebDriver driver) {
        this.driver = driver;
        this.wait = new WebDriverWait(driver, 10);
        PageFactory.initElements(driver, this);
    }

    public void login(String username, String password) {
        wait.until(ExpectedConditions.visibilityOf(usernameInput));
        usernameInput.sendKeys(username);
        passwordInput.sendKeys(password);
        loginButton.click();
    }
}