问移动自动化-测试非静态驱动程序- TakeScreenshot方法使用并行线程抛出NPE错误

EN

public class g_MobileBase {

    @SuppressWarnings("rawtypes")

    public  AndroidDriver driver=null;

    public DesiredCapabilities cap;

    @SuppressWarnings("rawtypes")
    public AndroidDriver InitializeDriver() throws IOException
    {//initialization code; return driver;
        }
        public void getScreenshot(String classname, String testname) throws IOException
    {
        File src = ((TakesScreenshot)driver).getScreenshotAs(OutputType.FILE);
        FileUtils.copyFile(src,new File(System.getProperty("user.dir")+"\\ErrorSnapshots\\"+classname+"_"+testname+"_"+new SimpleDateFormat("yyyy-MM-dd hh-mm-ss").format(new Date())+".png"));
    }
}

public class G_SearchStore_LocOff extends g_MobileBase{


    @BeforeTest (description="Initialize driver and install application")

    public void Initialize() throws IOException
    {

        this.driver = InitializeDriver();
//remaining code

}

@AfterTest (description="Close application and Quit driver")
    public void finish()
    {

        driver.closeApp();

        driver.quit();
}

@Test
.................some methods
.................some methods

}

public class g_testListener implements ITestListener{

g_MobileBase b = new g_MobileBase();

@Override
    public void onTestFailure(ITestResult result) {
        // TODO Auto-generated method stub

        String[] temp = result.getInstanceName().toString().split("\\.");
        String classname = temp[1];

        try {

            b.getScreenshot(classname,result.getName());
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

}