異常：java.lang.NullPointerException

Question

我正在使用以下代碼來驗證圖像是否已完全加載到網頁上。

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; 
    } 

運行此方法，而我得到以下異常

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")); 

讓我知道我在我缺少JavaScript代碼之上。

在此先感謝

Answer 1

1. typeof應該是一個單詞。這應該解決它。
2. 之後您可以返回imageLoaded1。無需輸入if條件。

UPDATE：

你可能會得到空指針異常，因爲executeScript返回null。我已經修改了代碼位（主要是我把支架，以確保邏輯運算符的正確順序）

試試這個：

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; 
    }