Question

我目前正在尝试使用android studio中的列表视图创建主 - 详细信息页面。

我创建了列表视图，创建了一个要放入其中的字符串数组，称为适配器，所有代码看起来都很好。

但是，当我在包含列表视图的应用程序中打开活动时，应用程序崩溃并说“不幸的是应用程序已停止工作”。

我会在下面附上错误代码和我的实际代码。任何帮助将不胜感激。

我的代码

public class PlaceList extends AppCompatActivity {

ListView listView;

ArrayAdapter<String> mAdapter = new ArrayAdapter<String>(PlaceList.this,
        android.R.layout.simple_list_item_1,
        getResources().getStringArray(R.array.countries));

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


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

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView,View view,int i,long l){
        Intent intent = new Intent(PlaceList.this,DetailsActivity.class);
        intent.putExtra("CountryName",listView.getItemAtPosition(i).toString());
        startActivity(intent);

        }
    });


    listView.setAdapter(mAdapter);



}

**关于崩溃的错误报告**

03-01 15:21:14.443 13699-13699/com.example.bradwaterhouse.discovernottingham 
E/AndroidRuntime: FATAL EXCEPTION: main

 Process: com.example.bradwaterhouse.discovernottingham, PID: 13699

 java.lang.RuntimeException: Unable to instantiate activity 

java.lang.NullPointerException:

 Attempt to invoke virtual method 'android.content.res.Resources 
 android.content.Context.getResources()' on a null object reference

 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3132)

 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
                                                                                               at android.app.ActivityThread.access$1100(ActivityThread.java:229)
                                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
                                                                                               at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                               at android.os.Looper.loop(Looper.java:148)
                                                                                               at android.app.ActivityThread.main(ActivityThread.java:7331)
                                                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
                                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference

at android.content.ContextWrapper.getResources(ContextWrapper.java:92)

at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81)

at 

 android.support.v7.app.AppCompatActivity.getResources
(AppCompatActivity.java:542)

at com.example.bradwaterhouse.discovernottingham.PlaceList.<init>
(PlaceList.java:17)

at java.lang.Class.newInstance(Native Method)

at android.app.Instrumentation.newActivity(Instrumentation.java:1096)

at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3122)

at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 

at android.app.ActivityThread.access$1100(ActivityThread.java:229) 

at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 

at android.os.Handler.dispatchMessage(Handler.java:102) 

at android.os.Looper.loop(Looper.java:148) 

at android.app.ActivityThread.main(ActivityThread.java:7331) 

 at java.lang.reflect.Method.invoke(Native Method) 

 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run
(ZygoteInit.java:1230) 

 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Answer 1

您需要onCreate()方法中的初始适配器。

Answer 2

如上文评论所述

mAdapter = new ArrayAdapter<String>(PlaceList.this, android.R.layout.simple_list_item_1, getResources().getStringArray(R.array.countries));

只需在oncreate中写下这一行

原因

您只能在活动生命周期的onCreate()或更高版本中将您的活动用作资源上下文

信用laalto

Android ListView崩溃的应用程序

2 个答案: