AsyncTask無法正常工作

Question

您能否檢查我的代碼並告訴我我錯過了什麼？它迫使關閉設備。

SplashScreen.java

package com.example.citylist; 


public class SplashScreen extends Activity { 

JSONObject jsonobject; 
JSONArray jsonarray; 
ProgressDialog progressBar; 
CityList list; 
public TextView tv; 
ArrayList<String> myList; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    //Hide the status bar 
    requestWindowFeature(Window.FEATURE_NO_TITLE); 
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
            WindowManager.LayoutParams.FLAG_FULLSCREEN); 

    setContentView(R.layout.splash_screen); 

    new DownloadJSON().execute(); 
} 

private class DownloadJSON extends AsyncTask<Void, Void, Void> { 

    @Override 
    protected void onPreExecute() { 
     super.onPreExecute(); 
//   progressBar = new ProgressDialog(MainActivity.this); 
//   progressBar.setTitle("City List"); 
//   progressBar.setMessage("Loading city list..."); 
//   progressBar.setIndeterminate(false); 
//   progressBar.show(); 
    } 

    @Override 
    protected Void doInBackground(Void... params) { 
     jsonarray = JSONfunctions.getJSONfromURL("http://m.kentkart.com/new/services/?cmd=getCityList", "city"); 

     list = new CityList(); 

     try { 
      for (int i = 0; i < jsonarray.length(); i++) { 
        JSONObject row; 

        row = jsonarray.getJSONObject(i); 

        CityInfo item = new CityInfo(); 

        item.setId(row.optString(ServiceConstant.id)); 
        item.setName(row.optString(ServiceConstant.name)); 


        list.addItem(item); 
       } 
      } 

     catch (JSONException e) { 
       Log.e("json","hey"); 
     }         
     return null; 
    } 

    @Override 
    protected void onPostExecute(Void args) { 

     myList = new ArrayList<String>(); 

     for (int i=0; i<list.getLength(); i++) 
     { 
      myList.add(list.getItem(i).getName().toString()); 
     } 

     Intent i = new Intent(getApplicationContext(), CityListView.class); 
     i.putStringArrayListExtra("name", myList); 
     startActivity(i); 
     finish(); 
    } 
} 
} 

Android清單

<uses-sdk 
    android:minSdkVersion="8" 
    android:targetSdkVersion="19" /> 
<uses-permission android:name="android.permission.INTERNET"></permission> 

<application 
    android:allowBackup="true" 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" 
    android:theme="@android:style/Theme.Light.NoTitleBar" > 
    <activity 
     android:name="com.example.citylist.SplashScreen" 
     android:label="@string/title_activity_main" > 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
    <activity android:name="com.example.citylist.CityListView"></activity> 

</application> 

logcat的

CityListView

package com.example.citylist; 

public class CityListView extends Activity { 

ArrayList<String> myList; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    //Hide the status bar 
    requestWindowFeature(Window.FEATURE_NO_TITLE); 
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
            WindowManager.LayoutParams.FLAG_FULLSCREEN);     
    setContentView(R.layout.city_list); 

    ListView theListView = (ListView) findViewById(R.id.cityList);   

    Intent i = getIntent(); 
    myList = i.getExtras().getStringArrayList("myList"); 

    ListAdapter theAdapter = new ArrayAdapter<String> 
    (CityListView.this, android.R.layout.simple_list_item_1, myList); 

    theListView.setAdapter(theAdapter); 

    //liste elemanlarına tıklanıldığında oluşmasını istediğimiz durumu yazıyoruz 
    theListView.setOnItemClickListener(
      new AdapterView.OnItemClickListener() { 

       @Override 
      public void onItemClick(AdapterView<?> parent, View view, 
         int position, long id) { 
        //seçilen liste elemanını ekrana toast mesajı ile yazdırıyoruz. 
        String chosenCity = "You selected " 
          +parent.getItemAtPosition(position); 
        Toast.makeText(CityListView.this, chosenCity, Toast.LENGTH_SHORT).show(); 

       } 
    }); 

} 

} 

下面是logcat的消息：

06-25 11:59:53.095: E/AndroidRuntime(7326): FATAL EXCEPTION: main 

06-25 11:59:53.095: E/AndroidRuntime(7326): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.citylist/com.example.citylist.CityListView}: java.lang.NullPointerException 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.app.ActivityThread.access$700(ActivityThread.java:140) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.os.Handler.dispatchMessage(Handler.java:99) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.os.Looper.loop(Looper.java:137) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.app.ActivityThread.main(ActivityThread.java:4921) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at java.lang.reflect.Method.invokeNative(Native Method) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at java.lang.reflect.Method.invoke(Method.java:511) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at dalvik.system.NativeStart.main(Native Method) 

06-25 11:59:53.095: E/AndroidRuntime(7326): Caused by: java.lang.NullPointerException 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.widget.ListView.setAdapter(ListView.java:466) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at com.example.citylist.CityListView.onCreate(CityListView.java:38) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.app.Activity.performCreate(Activity.java:5206) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074) 

06-25 11:59:53.095: E/AndroidRuntime(7326):  ... 11 more 

Answer 1

試試這個..

您在名鍵名狀i.putStringArrayListExtra("name", myList);但您的發送ArrayList接收密鑰名稱myList使myList是空

更改這個..

myList = i.getExtras().getStringArrayList("myList"); 

到

myList = i.getStringArrayListExtra("name");