Question

我正在尝试创建一个ListView，但是适配器似乎崩溃导致空点异常

代码：

public void navMenuSetup()
{
    mDrawerLayout = (DrawerLayout)findViewById(R.id.nav_layout);
    mDrawerList = (ListView)findViewById(R.id.nav_listview);
    navDrawerItems = new ArrayList<String>();
    String[] navMenuItem = new String[]{"about","Stories","Donate","Gallery"};

    navDrawerItems.add(navMenuItem[0]);
    navDrawerItems.add(navMenuItem[1]);
    navDrawerItems.add(navMenuItem[2]);
    navDrawerItems.add(navMenuItem[3]);

    ArrayAdapter<String> itemsAdapter = new ArrayAdapter<String>(this,android.R.layout.activity_list_item,navMenuItem);
    mDrawerList.setAdapter(itemsAdapter);

    getActionBar().setDisplayHomeAsUpEnabled(true);
    getActionBar().setHomeButtonEnabled(true);




}

logcat的：

03-31 00:39:42.548  15014-15014/actionandroid.aa.com.actionandroid E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: actionandroid.aa.com.actionandroid, PID: 15014
    java.lang.RuntimeException: Unable to start activity ComponentInfo{actionandroid.aa.com.actionandroid/actionandroid.aa.com.actionandroid.AboutActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
            at actionandroid.aa.com.actionandroid.AboutActivity.navMenuSetup(AboutActivity.java:44)
            at actionandroid.aa.com.actionandroid.AboutActivity.onCreate(AboutActivity.java:59)
            at android.app.Activity.performCreate(Activity.java:5933)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

它似乎是由arrayAdapter使用null对象引起的，但是在我的生活中找出什么是null。

Answer 1

问题似乎与您创建ListView的方式有关。我不能完全从你发布的代码中说出来但是Udacity对android dev有很好的介绍，他们会通过ArrayAdapter创建一个ListView。

以下是其代码的链接：https://github.com/udacity/Sunshine/blob/1.06-bind-adapter-to-list-view/app/src/main/java/com/example/android/sunshine/app/MainActivity.java

Answer 2

您是否忘记在活动中调用setContentView？如果您这样做，请检查您引用的布局是否包含具有id nav_listview

的列表

Android setAdapter null对象引用

2 个答案: