ListView 适配器崩溃活动

Question

就像在 subcjet 中一样。当我评论 listView.setAdapter(adapter); 它只是显示另一个活动：

这是整个 onCreate：

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_lista__klas);

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }

        klasy = getResources().getStringArray(R.array.klasy);

        ListView listView = (ListView)findViewById(R.id.lista_klas);
        adapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.activity_lista__klas);
        listView.setAdapter(adapter);
    }

当我按下启动此活动的按钮时，从 logcat 记录：

11-20 13:14:53.085    1494-1780/system_process I/ActivityManager﹕ START {cmp=pl.krasiniak.krachapp_beta/.Lista_Klas} from pid 3975
11-20 13:14:53.335    3975-3975/pl.krasiniak.krachapp_beta D/AndroidRuntime﹕ Shutting down VM
11-20 13:14:53.335    3975-3975/pl.krasiniak.krachapp_beta W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x40a521f8)
11-20 13:14:53.345    3975-3975/pl.krasiniak.krachapp_beta E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{pl.krasiniak.krachapp_beta/pl.krasiniak.krachapp_beta.Lista_Klas}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2079)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2104)
            at android.app.ActivityThread.access$600(ActivityThread.java:132)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1157)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4575)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at pl.krasiniak.krachapp_beta.Lista_Klas.onCreate(Lista_Klas.java:34)
            at android.app.Activity.performCreate(Activity.java:4465)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2033)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2104)
            at android.app.ActivityThread.access$600(ActivityThread.java:132)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1157)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4575)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
            at dalvik.system.NativeStart.main(Native Method)
11-20 13:14:53.355    1494-1675/system_process W/ActivityManager﹕ Force finishing activity pl.krasiniak.krachapp_beta/.Lista_Klas
11-20 13:14:53.355    1494-1675/system_process W/ActivityManager﹕ Force finishing activity pl.krasiniak.krachapp_beta/.MainActivity
11-20 13:14:53.865    1494-1509/system_process W/ActivityManager﹕ Activity pause timeout for ActivityRecord{40ef3f48 pl.krasiniak.krachapp_beta/.Lista_Klas}
11-20 13:14:54.065    3215-3215/com.cyanogenmod.trebuchet W/Adreno200-EGLSUB﹕ SetSwapInterval() interval: 0 not set
11-20 13:14:54.105    1494-1506/system_process I/ActivityManager﹕ No longer want com.android.keychain (pid 3950): hidden #16
11-20 13:15:04.105    1494-1509/system_process W/ActivityManager﹕ Activity destroy timeout for ActivityRecord{40ebf3c0 pl.krasiniak.krachapp_beta/.MainActivity}
11-20 13:15:04.105    1494-1509/system_process W/ActivityManager﹕ Activity destroy timeout for ActivityRecord{40ef3f48 pl.krasiniak.krachapp_beta/.Lista_Klas}

我确定数组不为空。谢谢你的回答，问候:)

Answer 1

代码不正确：

setContentView(R.layout.activity_lista__klas);

// ...

ListView listView = (ListView)findViewById(R.id.lista_klas);
adapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.activity_lista__klas);

内容视图和数组适配器使用相同的布局。当使用two-argument constructor of ArrayAdapter 时，资源ID 必须解析为单个TextView。 findViewById() 调用意味着它是一个更复杂的布局，带有 ListView。

如果我正确理解您的意图，请执行以下操作：

• 确保activity_list__klas 包含具有指定ID lista_klas 的ListView，以便findViewById() 返回非null。

• 将适配器构造函数的布局资源 ID 更改为包含单个 TextView 的资源文件，该 TextView 代表您的列表行。或者更改为允许您指定映射数组项的TextViews 的另一个构造函数重载。

• 向适配器提供一些数据以实际显示某些内容。

Answer 2

试试这个。添加第三个参数

adapter = new ArrayAdapter<String>(getApplicationContext(),R.layout.activity_lista__klas,klasy);

如果这不起作用。请也粘贴您的布局文件。

Answer 3

我猜你的问题在这里：

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

检查您是否有一个具有此 ID 的 ListView 并且 listView 不为空。

此外，当您创建适配器时，您需要将包含单个 TextView 的布局文件传递给 ArrayAdapter，以用于显示每个列表项。您已经传递了在 setContentView 中使用的相同布局，（我假设）是您的活动的完整布局。