PHP中的PDO：fetch（）不起作用

Question

这是我的代码：

@Test
public void testBothAppAndSafari() throws MalformedURLException {
    URL appiumServerUrl = new URL("<your appium server host>");
    DesiredCapabilities appCaps = new DesiredCapabilities();
    // put required native app capabilities in appCaps
    DesiredCapabilities safariCaps = new DesiredCapabilities();
    // put required safari capabilities in safariCaps

    IOSDriver driver = new IOSDriver(appiumServerUrl, appCaps);
    driver.findElement(<locator for element in native app>).click();
    // do whatever you want with mobile app
    driver.quit();

    driver = new IOSDriver(appiumServerUrl, safariCaps);
    driver.findElement(<locator for element in web>).click();
    // do whatever you want in safari
    driver.quit();
}

但它显示错误：

致命错误：在布尔上调用成员函数fetchAll（）

为什么它不起作用？

谢谢。