Question

与子飞机一样。当我评论listView.setAdapter(adapter);时，它只显示另一项活动：

这完全是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);
    }

当我按下开始此活动的按钮时，从logcat登录：

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}

我确定数组不是空的。谢谢你的回答，问候：）

Answer 1

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。请粘贴您的布局文件。

Answer 2

我猜你的问题就在这里：

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

检查您是否拥有包含此ID的ListView且listView不为空。

此外，在创建适配器时，您需要传递ArrayAdapter包含单个TextView的布局文件，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，其中（我假设）是您活动的完整布局。

Answer 3

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。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，其中包含ListView。

如果我理解您的意图正确，请执行以下操作：

确保activity_list__klas包含具有指定ID ListView的{{1}}，以便lista_klas返回非findViewById()。
将适配器构造函数的布局资源ID更改为包含表示列表行的单个null的资源文件。或者更改为另一个构造函数重载，允许您指定映射数组项的TextView。
向适配器提供一些数据以实际显示内容。

ListView适配器崩溃活动

3 个答案: