Question

请你检查我的代码并告诉我我想念的是什么？它迫使设备关闭。

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 Manifest

<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

enter image description here

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();

                }
    });

}

}

以下是Logcat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

试试这个..

您正在发送ArrayList的密钥名称名称，例如i.putStringArrayListExtra("name", myList);，但您的密钥名称为 myList ，以便{{} 1}}是 null

改变这个..

myList

到

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

AsyncTask无法正常工作

1 个答案: