Question

我在我的Android代码中遇到以下异常，但我无法弄明白。我已使用TabActivity扩展了我的主页活动，并从MainActivity接收了其中的意图。在tab3中，我已经将意图传递给另一个活动，该活动将在选择tab3时开始。来自该意图的数据正在该活动中收到。我已经通过Log检查了它。收到的数据将显示在该活动的ListView中。但不幸的是我的应用程序崩溃了。对此有何帮助？
这是我的logcat。

01-24 14:36:34.880: E/AndroidRuntime(1147): FATAL EXCEPTION: main
01-24 14:36:34.880: E/AndroidRuntime(1147): Process: com.example.app, PID: 1147
01-24 14:36:34.880: E/AndroidRuntime(1147): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.app/com.example.app.Home1}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.app/com.example.app.CameraList}: java.lang.NullPointerException
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.ActivityThread.access$700(ActivityThread.java:135)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.os.Looper.loop(Looper.java:137)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.ActivityThread.main(ActivityThread.java:4998)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at java.lang.reflect.Method.invokeNative(Native Method)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at java.lang.reflect.Method.invoke(Method.java:515)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at dalvik.system.NativeStart.main(Native Method)
01-24 14:36:34.880: E/AndroidRuntime(1147): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.app/com.example.app.CameraList}: java.lang.NullPointerException
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.ActivityThread.startActivityNow(ActivityThread.java:2019)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:135)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:347)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:749)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.widget.TabHost.setCurrentTab(TabHost.java:413)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.widget.TabHost.addTab(TabHost.java:240)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at com.example.app.Home1.setNewTab(Home1.java:136)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at com.example.app.Home1.onCreate(Home1.java:83)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.Activity.performCreate(Activity.java:5243)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
01-24 14:36:34.880: E/AndroidRuntime(1147):     ... 11 more
01-24 14:36:34.880: E/AndroidRuntime(1147): Caused by: java.lang.NullPointerException
01-24 14:36:34.880: E/AndroidRuntime(1147):     at com.example.app.CameraList.onCreate(CameraList.java:40)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.Activity.performCreate(Activity.java:5243)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-24 14:36:34.880: E/AndroidRuntime(1147):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
01-24 14:36:34.880: E/AndroidRuntime(1147):     ... 22 more

这是我在家庭活动中使用标签的地方..

String [] names;
names = intent.getStringArrayExtra("name");
    if(tag.equals("tab3"))
    {
        Intent ListIntent = new Intent(this, List.class);
        ListIntent.putExtra("itemName", names);
        tabSpec.setContent(ListIntent);
        tabHost.addTab(tabSpec);
    }

我在OnCreate方法中接收意图的活动：

public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.cam_list);

    //Log.i("cam","List");

    Intent intent = getIntent();
    name = intent.getStringArrayExtra("camName");
    //Log.i("cam", name[1]);
    url = intent.getStringArrayExtra("url");

    list = (ListView)findViewById(R.id.listView);

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,R.layout.cam_list,R.id.text1, name);
    list.setAdapter(adapter);
    /*list.setOnItemClickListener(new OnItemClickListener() {

         @Override
         public void onItemClick(AdapterView<?> parent, View view,
            int position, long id) {

              // ListView Clicked item value
              String  itemValue    = (String) list.getItemAtPosition(position);
              String camUrl = url[position];

               // Show Alert 
               Toast.makeText(getApplicationContext(),camUrl,Toast.LENGTH_LONG).show();
         }
    });*/
}

Answer 1

如果您从NullPointerException检索到的View获得findViewById()，则Android会告诉您View不存在。这里有两种主要的可能性：

View确实不存在，例如在您需要时无法拨打setContentView()。
如果您使用的是Eclipse，有时R常量会与APK文件的内容不同步。要解决此问题，请选择项目＆gt;从Eclipse主菜单中清除，然后再次尝试运行您的应用程序。幸运的是，我没有在Android Studio中看到这种行为（感谢$DEITY获得小优惠......）。

java.lang.RuntimeException：无法启动活动组件信息（Android）

1 个答案: