java - 安卓ListView报错

Question

我有一个用来接收一些信息的方法。我向此方法发送一个字符串(服务器方向)和两个包含用户和密码的字符串，然后我收到一个包含所有信息的 String[]。然后我在 ArrayAdapter 上使用 String[] 值，但是 logcat 上显示错误，我不知道为什么会出现此错误...在预览版本中，我使用自己的值，没有“String[] 值”它工作完美，但现在我不知道为什么它不起作用。

String[] values;

@SuppressLint("InlinedApi")
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_USER_LANDSCAPE);
    setContentView(R.layout.activity_select_environment);   

    myBundle = getIntent().getExtras();

    user = myBundle.getString("user");
    password = myBundle.getString("password");

    values = request("http://myIp/XXX/post.php?request=1", user, password);  

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_expandable_list_item_1, android.R.id.text1, values);
}

另一种方法是下一个:

    public String[] request(String requesturl, String user, String password)
{
    String result[] = new String[100]; 

    try
    {
        HttpClient httpclient = new DefaultHttpClient(); 

        HttpPost httppost = new HttpPost(requesturl);

        String results = "";

        //Varibles POST
        List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
        nameValuePairs.add(new BasicNameValuePair("user", user));
        nameValuePairs.add(new BasicNameValuePair("password", password));                        

        httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

        //Execute HTTP Post Request
        HttpResponse response = httpclient.execute(httppost);
        response.getAllHeaders();
        response.getEntity();
        result[0] = "";                                                                         
        if(response.getStatusLine().getStatusCode() == HttpStatus.SC_OK)
        {
            results = EntityUtils.toString(response.getEntity());           
            if(!results.equals("-1"))
            {
                JSONObject jsonResponse = new JSONObject(results);

                JSONArray jsonMainNode = jsonResponse.optJSONArray("edificios");

                int lengthJsonArr =jsonMainNode.length();
                for(int i = 0; i < lengthJsonArr; i++)
                {
                    JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);   
                    result[i] = jsonChildNode.optString("nombre"); 
                }
            }                 
        }

        return result;
    }
    catch(Exception ex)
    {
        result[0] = "error";
        return result;
    }
}  

这是错误的日志。

03-31 09:02:22.920: W/dalvikvm(2016): threadid=1: thread exiting with uncaught exception (group=0xb3b0ab90)
03-31 09:02:22.950: E/AndroidRuntime(2016): FATAL EXCEPTION: main
03-31 09:02:22.950: E/AndroidRuntime(2016): Process: com.example.en4dis, PID: 2016
03-31 09:02:22.950: E/AndroidRuntime(2016): java.lang.NullPointerException
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.widget.AbsListView.obtainView(AbsListView.java:2240)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.widget.ListView.measureHeightOfChildren(ListView.java:1263)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.widget.ListView.onMeasure(ListView.java:1175)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.View.measure(View.java:16458)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.widget.RelativeLayout.measureChild(RelativeLayout.java:689)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:473)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.View.measure(View.java:16458)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.View.measure(View.java:16458)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.View.measure(View.java:16458)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2289)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.View.measure(View.java:16458)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1914)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1111)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1293)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5582)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.Choreographer.doCallbacks(Choreographer.java:562)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.Choreographer.doFrame(Choreographer.java:532)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.os.Handler.handleCallback(Handler.java:733)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.os.Handler.dispatchMessage(Handler.java:95)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.os.Looper.loop(Looper.java:137)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at android.app.ActivityThread.main(ActivityThread.java:4998)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at java.lang.reflect.Method.invokeNative(Native Method)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at java.lang.reflect.Method.invoke(Method.java:515)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
03-31 09:02:22.950: E/AndroidRuntime(2016):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

我认为您的问题在这里:

String result[] = new String[100]; 

您初始化了一个长度为 100 的数组。现在您只填充了数组的一部分。这意味着在你的内存中你将会有这样的东西

Index:       0       1            98     99
Values:   Value1 | Value2| ... | null | null

(编辑:我知道这并不完全准确，因为只存储了引用，但这样更容易理解)

现在，当您将其传递给 ArrayAdapter 时，它将解析每个元素，最后它将尝试使用 null 作为字符串来布局 TextView。显然Android不喜欢这样。

您要做的就是获取一个与您的值的长度完全相同的数组。我建议先使用列表，然后再创建数组。例如(未测试伪代码)

public String[] request(String requesturl, String user, String password){

   //init List
   List<String> values = new ArrayList<String>(); 

   //add values to List like this
   values.add("myString");


   //return a array with the correct size at last
   return  values.toArray(new String[values.size()]);

}  

确保对您的错误情况也执行相同的操作。