如何解決由意圖引起的空指針異常

Question

將第三個活動添加到我的代碼后，我遇到了錯誤。 生成錯誤的代碼如下：

public void onClick(View v) {
            Intent callIncomeIntent = new Intent(v.getContext(), Add_Income.class);
            startActivityForResult(callIncomeIntent, 0);
        }
    });

產生錯誤：

11-18 13:59:29.137: D/libEGL(13211): loaded /vendor/lib/egl/libEGL_adreno.so
11-18 13:59:29.147: D/libEGL(13211): loaded /vendor/lib/egl/libGLESv1_CM_adreno.so
11-18 13:59:29.147: D/libEGL(13211): loaded /vendor/lib/egl/libGLESv2_adreno.so
11-18 13:59:29.157: I/Adreno-EGL(13211): <qeglDrvAPI_eglInitialize:316>: EGL 1.4 QUALCOMM build:  (CL4169980)
11-18 13:59:29.157: I/Adreno-EGL(13211): OpenGL ES Shader Compiler Version: 17.01.10.SPL
11-18 13:59:29.157: I/Adreno-EGL(13211): Build Date: 11/04/13 Mon
11-18 13:59:29.157: I/Adreno-EGL(13211): Local Branch: 
11-18 13:59:29.157: I/Adreno-EGL(13211): Remote Branch: 
11-18 13:59:29.157: I/Adreno-EGL(13211): Local Patches: 
11-18 13:59:29.157: I/Adreno-EGL(13211): Reconstruct Branch: 
11-18 13:59:29.197: D/OpenGLRenderer(13211): Enabling debug mode 0
11-18 13:59:31.800: D/AndroidRuntime(13211): Shutting down VM
11-18 13:59:31.800: W/dalvikvm(13211): threadid=1: thread exiting with uncaught exception (group=0x415b58b0)
11-18 13:59:31.830: E/AndroidRuntime(13211): FATAL EXCEPTION: main
11-18 13:59:31.830: E/AndroidRuntime(13211): java.lang.RuntimeException: Unable to start activity ComponentInfo{tei.ptix.income_management/tei.ptix.income_management.Add_Income}: java.lang.NullPointerException
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2266)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2316)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.app.ActivityThread.access$600(ActivityThread.java:150)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1298)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.os.Looper.loop(Looper.java:213)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.app.ActivityThread.main(ActivityThread.java:5225)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at java.lang.reflect.Method.invokeNative(Native Method)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at java.lang.reflect.Method.invoke(Method.java:525)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:741)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at dalvik.system.NativeStart.main(Native Method)
11-18 13:59:31.830: E/AndroidRuntime(13211): Caused by: java.lang.NullPointerException
11-18 13:59:31.830: E/AndroidRuntime(13211):    at tei.ptix.income_management.Add_Income.onCreate(Add_Income.java:31)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.app.Activity.performCreate(Activity.java:5133)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-18 13:59:31.830: E/AndroidRuntime(13211):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2230)
11-18 13:59:31.830: E/AndroidRuntime(13211):    ... 11 more

當我將鼠標懸停在Intent上時，它會顯示以下文本：android.content.Intent.Intent（Context packageContext，Class注意：此元素沒有附加的源，並且在附加的Javadoc中找不到Javadoc。

有人可以提出解決方案嗎？

提前致謝。

Answer 1

11-18 13:59:31.830: E/AndroidRuntime(13211): Caused by: java.lang.NullPointerException
11-18 13:59:31.830: E/AndroidRuntime(13211):    at tei.ptix.income_management.Add_Income.onCreate(Add_Income.java:31)

有人編寫了一個名為tei.ptix.income_management.Add_Income的Java類。 從上面的代碼段來看，它似乎是Activity的子類。 在其onCreate()方法中，在Add_Income.java第31行中，您具有NullPointerException 。

因此，請看一下Add_Income.java第31行，並確定為什么要對某些參數，變量或為null數據成員調用方法。 如果您不能確定為什么它為null ，則可以考慮問一個問題，在哪里為活動提供源代碼，或者至少在onCreate()方法中指出哪一行是第31行，並且有人可以提供幫助。您確定什么為null以及為什么。