安卓:使用2个ArrayAdapters错误

Question

我现在得到一个新的错误。

这是我的代码：

lv.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
    @Override
    public boolean onItemLongClick(AdapterView<?> arg0, View arg1, int i, long id) {
        Toast.makeText(getApplicationContext(), beaconAdap.getItem(i).toString() + " Added to history", Toast.LENGTH_SHORT).show();
        historyBeacons.add(beaconAdap.getItem(i).toString());
        Intent intent = new Intent(getBaseContext(), HistoryActivity.class);
        intent.putStringArrayListExtra("beacons", historyBeacons);
        startActivity(intent);
        return true;
    }
});

}

因此，我将int i添加到数组列表中，我测试了它是否正确，它确实有效。然后，为历史活动开始一个新的意图，并发送数组列表。

以下是历史记录中的代码：

ListView historyLv = (ListView) findViewById(R.id.historyView);
ArrayAdapter historyAdap;
ArrayList<String> historyBeacons = getIntent().getExtras().getStringArrayList("beacons");

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_history);
    historyAdap = new ArrayAdapter(getApplicationContext(), android.R.layout.simple_list_item_1, historyBeacons);
    historyLv.setAdapter(historyAdap);
}

但是我得到了这个错误：

03-18 17:44:41.238 18641-18641/nsa.com.museum E/AndroidRuntime: FATAL EXCEPTION: main
                                                                Process: nsa.com.museum, PID: 18641
                                                                java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{nsa.com.museum/nsa.com.museum.HistoryActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                    at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                    at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                    at android.os.Looper.loop(Looper.java:148)
                                                                    at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
                                                                    at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:120)
                                                                    at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:151)
                                                                    at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:31)
                                                                    at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:55)
                                                                    at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:33)
                                                                    at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:203)
                                                                    at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:185)
                                                                    at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
                                                                    at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
                                                                    at nsa.com.museum.HistoryActivity.<init>(HistoryActivity.java:12)
                                                                    at java.lang.Class.newInstance(Native Method)
                                                                    at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)
                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                    at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                    at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                    at android.os.Looper.loop(Looper.java:148) 
                                                                    at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                    at java.lang.reflect.Method.invoke(Native Method) 
                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
03-18 17:44:43.362 18846-18846/nsa.com.museum W/System: ClassLoader referenced unknown path: /data/app/nsa.com.museum-2/lib/x86_64

Answer 1

你能给我看一下错误吗?我猜你忘了加上

    ListAdapter.notifyDataSetChanged();

将值添加到lisy之后

.........................................................

NullPointerException

此错误在Android中显示原因您可能无法初始化适配器请确保您已初始化第二个适配器