异常：java.lang.NullPointerException

Question

I am using the following code to verify whether the image has loaded completely on a webpage or not.

public static boolean IsImageVisible1(WebDriver driver, By locator)
  {
    WebElement image = driver.findElement(locator);
    //if the element not present you'll get the NoSuchElementException exception
    JavascriptExecutor js = (JavascriptExecutor) driver;
    boolean imageLoaded1  = (boolean) js.executeScript("return arguments[0].complete && (typeof arguments[0].naturalWidth !== \"undefined\") && (arguments[0].naturalWidth > 0)", image);      
    return imageLoaded1;
  }

while running this method i am getting following exception

java.lang.NullPointerException
at pack2.image.IsImageVisible1(image.java:58)
at pack2.image.test(image.java:23)
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.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)


function call to above method: IsImageVisible1(driver, By.id("homepage-preview"));

let me know what i am missing in the above javascript code.

Thanks in advance

Answer 1

1. typeof should be one word. And that should fix it.
2. You can just return imageLoaded1 after that. No need to put the if condition.

UPDATE:

You are probably getting the NullPointer Exception because executeScript returns null. I've modified the code a bit (mainly I put the brackets to make sure the correct order of logical operators)

try this:

public static boolean IsImageVisible1(WebDriver driver, By locator)
  {
    WebElement image = driver.findElement(locator);
    //if the element not present you'll get the NoSuchElementException exception
    JavascriptExecutor js = (JavascriptExecutor) driver;
    boolean imageLoaded1  = (boolean) js.executeScript("return arguments[0].complete && (typeof arguments[0].naturalWidth !== \"undefined\") && (arguments[0].naturalWidth > 0)", image);      
    return imageLoaded1;
  }