JSON的網址不工作

我想從服務器調用JSON數組JSON的網址不工作

這條線工作正常，我

JSONObject json = JSONfunctions.getJSONfromURL("http://midsweden.gofreeserve.com/fetch.php");

但是當我嘗試使用我的sharedprefences類來獲取它不工作，CME與力停下來，這裏是代碼

JSONObject json = JSONfunctions.getJSONfromURL("http://midsweden.gofreeserve.com/fetch.php?identifier=" 
       + Test.this.myprefs.getEmail());

在日食它不指向任何錯誤我的意思是缺少變種減速，但它不工作。任何建議？

以下是我在logcat的

05-02 19:49:53.569: ERROR/AndroidRuntime(20721): Uncaught handler: thread main exiting due to uncaught exception 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.droidnova.android.howto.optionmenu/com.droidnova.android.howto.optionmenu.Test}: java.lang.NullPointerException 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2596) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2621) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at android.app.ActivityThread.access$2200(ActivityThread.java:126) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1932) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at android.os.Looper.loop(Looper.java:123) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at android.app.ActivityThread.main(ActivityThread.java:4595) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at java.lang.reflect.Method.invoke(Method.java:521) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at dalvik.system.NativeStart.main(Native Method) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): Caused by: java.lang.NullPointerException 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at com.droidnova.android.howto.optionmenu.Test.onCreate(Test.java:37) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2544) 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  ... 11 more 
05-02 19:49:53.778: ERROR/ActivityManager(97): fail to set top app changed! 
05-02 19:49:58.048: ERROR/PackageInstallationReceiver(248): Remove /data/local/tmp/com.droidnova.android.howto.optionmenu.apk Fail! 
05-02 19:51:41.418: ERROR/AndroidRuntime(20746): ERROR: thread attach failed 
05-02 19:51:42.818: ERROR/AndroidRuntime(20754): ERROR: thread attach failed 
05-02 19:51:43.438: ERROR/AndroidRuntime(20762): Uncaught handler: thread main exiting due to uncaught exception 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.droidnova.android.howto.optionmenu/com.droidnova.android.howto.optionmenu.Test}: java.lang.NullPointerException 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2596) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2621) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at android.app.ActivityThread.access$2200(ActivityThread.java:126) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1932) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at android.os.Looper.loop(Looper.java:123) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at android.app.ActivityThread.main(ActivityThread.java:4595) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at java.lang.reflect.Method.invoke(Method.java:521) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at dalvik.system.NativeStart.main(Native Method) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): Caused by: java.lang.NullPointerException 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at com.droidnova.android.howto.optionmenu.Test.onCreate(Test.java:37) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2544) 
05-02 19:51:43.448: ERROR/AndroidRuntime(20762):  ... 11 more 
05-02 19:51:45.178: ERROR/ActivityManager(97): fail to set top app changed! 
05-02 19:51:54.428: ERROR/AndroidRuntime(20772): ERROR: thread attach failed 
05-02 19:51:55.818: ERROR/AndroidRuntime(20780): ERROR: thread attach failed 
05-02 19:51:56.528: ERROR/AndroidRuntime(20788): Uncaught handler: thread main exiting due to uncaught exception 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.droidnova.android.howto.optionmenu/com.droidnova.android.howto.optionmenu.Test}: java.lang.NullPointerException 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2596) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2621) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at android.app.ActivityThread.access$2200(ActivityThread.java:126) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1932) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at android.os.Looper.loop(Looper.java:123) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at android.app.ActivityThread.main(ActivityThread.java:4595) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at java.lang.reflect.Method.invoke(Method.java:521) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at dalvik.system.NativeStart.main(Native Method) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): Caused by: java.lang.NullPointerException 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at com.droidnova.android.howto.optionmenu.Test.onCreate(Test.java:37) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2544) 
05-02 19:51:56.538: ERROR/AndroidRuntime(20788):  ... 11 more 
05-02 19:51:58.658: ERROR/ActivityManager(97): fail to set top app changed! 
05-02 19:55:31.438: ERROR/AndroidRuntime(20809): ERROR: thread attach failed 
05-02 19:55:38.148: ERROR/AndroidRuntime(20820): ERROR: thread attach failed 
05-02 19:55:41.638: ERROR/PackageInstallationReceiver(248): Remove /data/local/tmp/com.droidnova.android.howto.optionmenu.apk Fail! 
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key 
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key 
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key 
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key 
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key 
05-02 20:15:29.648: ERROR/wpa_supplicant(139): prepare_filter_struct: type=5 
05-02 20:15:32.728: ERROR/wpa_supplicant(139): prepare_filter_struct: type=5

更多更詳細的我在這裏看到的是Test類

public class Test extends ListActivity { 
    Prefs myprefs = null; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.listplaceholder); 
     ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>(); 

     JSONObject json = JSONfunctions.getJSONfromURL("http://midsweden.gofreeserve.com/fetch.php?identifier=" 
      + Test.this.myprefs.getEmail()); 

     try{ 

      JSONArray earthquakes = json.getJSONArray("earthquakes"); 

      for(int i=0;i<earthquakes.length();i++){       
       HashMap<String, String> map = new HashMap<String, String>();  
       JSONObject e = earthquakes.getJSONObject(i); 

       map.put("id", String.valueOf(i)); 
       map.put("name", "Earthquake name:" + e.getString("name")); 
       map.put("password", "Magnitude: " + e.getString("password")); 
       mylist.add(map);    
      }  
     }catch(JSONException e)  { 
      Log.e("log_tag", "Error parsing data "+e.toString()); 
     } 

     ListAdapter adapter = new SimpleAdapter(this, mylist , R.layout.test, 
         new String[] { "name", "magnitude" }, 
         new int[] { R.id.item_title, R.id.item_subtitle }); 

     setListAdapter(adapter); 

     final ListView lv = getListView(); 
     lv.setTextFilterEnabled(true); 
     lv.setOnItemClickListener(new OnItemClickListener() { 
      public void onItemClick(AdapterView<?> parent, View view, int position, long id) {    
       @SuppressWarnings("unchecked") 
       HashMap<String, String> o = (HashMap<String, String>) lv.getItemAtPosition(position);     
       Toast.makeText(Test.this, "ID '" + o.get("id") + "' was clicked.", Toast.LENGTH_SHORT).show(); 

      } 
     }); 
    }

，這裏是共享的喜好類

package com.droidnova.android.howto.optionmenu; 

import android.content.Context; 
import android.content.SharedPreferences; 
import android.content.SharedPreferences.Editor; 

public class Prefs { 

    private SharedPreferences _prefs = null; 
    private Editor _editor = null; 
    private String _useremailaddress = "Unknown"; 
    private String _serverurl = "http://chinar.gofreeserve.com/db.php"; 

    public Prefs(Context context) { 
     this._prefs = context.getSharedPreferences("PREFS_PRIVATE", Context.MODE_PRIVATE); 
     this._editor = this._prefs.edit(); 
    } 

    public String getValue(String key, String defaultvalue) { 
     if (this._prefs == null) { 
      return "Unknown"; 
     } 

     return this._prefs.getString(key, defaultvalue); 
    } 

    public void setValue(String key, String value) { 
     if (this._editor == null) { 
      return; 
     } 

     this._editor.putString(key, value); 

    } 

    public String getEmail() { 
     if (this._prefs == null) { 
      return "Unknown"; 
     } 

     this._useremailaddress = this._prefs.getString("emailaddress", "noidea"); 
     return this._useremailaddress; 
    } 

    public String getServer() { 
     if (this._prefs == null) { 
      return "http://chinar.gofreeserve.com"; 
     } 

     this._serverurl = this._prefs.getString("serverurl", "http://chinar.gofreeserve.com/"); 
     return this._serverurl; 
    } 

    public void setEmail(String newemail) { 
     if (this._editor == null) { 
      return; 
     } 

     this._editor.putString("emailaddress", newemail); 
    } 

    public void setServer(String serverurl) { 
     if (this._editor == null) { 
      return; 
     } 
     this._editor.putString("serverurl", serverurl); 
    } 

    public void save() { 
     if (this._editor == null) { 
      return; 
     } 
     this._editor.commit(); 
    } 
}

來源

2011-05-02 umar

FC中會出現什麼樣的異常？請分享你的堆棧跟蹤。還有，'myprefs'成員的初始化。謝謝！ – rekaszeru 2011-05-02 18:09:44

你得到什麼樣的錯誤？請發佈相關部分的logcat。 – 2011-05-02 18:10:47

是Test.this.myprefs.getEmail（）url編碼的？ – 2011-05-02 18:12:54

你myPrefs var爲空

public class Test extends ListActivity { 
Prefs myprefs = null; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.listplaceholder); 
    ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>(); 

//myprefs can only be null at this point, you need this line or an equivalent for your Prefs class: 
myprefs = PreferenceManager.getDefaultSharedPreferences(this); 

    JSONObject json = JSONfunctions.getJSONfromURL("http://midsweden.gofreeserve.com/fetch.php?identifier=" 
     + Test.this.myprefs.getEmail());

API：

getDEfaultSharedPrefs()

或

getSharedPrefs()

編輯

啊，是你使用一些自定義的喜好類，所以你必須實例化這個類。

// Your choice of 
    Prefs myprefs = new Prefs(); 
    Prefs myprefs = new Prefs(this); 
    Prefs myprefs = new Prefs(getApplicationContext());

getApplicationContext()

，或者如果他的方法你希望使用的是靜態的：

Prefs.getEmail();

對此有閱讀：（！10號和1號）Top Ten Java Errors

來源

2011-05-02 18:52:44 Blundell

我已經用Prefs myprefs嘗試過了;但它不起作用，並且Prefs myprefs = new Prefs（）;我應該傳遞給Prefs（）的參數是因爲在prefs類中，它的一個arg構造函數就像這樣：public Prefs（Context context）{this._prefs = context.getSharedPreferences（「PREFS_PRIVATE」，Context.MODE_PRIVATE）; this._editor = this._prefs.edit（）; } – umar 2011-05-02 19:08:01

好的，所以你Prefs類包裝了SharedPreferences。只需傳遞活動上下文Prefs myPrefs = new Prefs（this）;在onCreate – Blundell 2011-05-02 19:09:07

當我declear這個Prefs myPrefs = new Prefs（this）;在oncreate然後在Test.this.myprefs.getEmail（）myprefs將不會宣佈和外面也不工作:( – umar 2011-05-02 19:32:59

你有一個空指針異常在代碼：

Caused by: java.lang.NullPointerException 
05-02 19:49:53.688: ERROR/AndroidRuntime(20721):  at com.droidnova.android.howto.optionmenu.Test.onCreate(Test.java:37)

修復此所以至少是你的應用程序將運行。

來源

2011-05-02 18:41:10 JoxTraex

我認爲有共享pref bcz的箴言，即使這是爲我工作的F9 JSONObject json = JSONfunctions.getJSONfromURL（「http://midsweden.gofreeserve.com/fetch.php?identifier=」 + 5）; – umar 2011-05-02 18:49:39

你是因爲（最有可能）得到的NullPointerException您myprefs爲null。

你在哪裏初始化這個領域？

總之，保存引用，而不是創建自己的解決方案，你應該看看Shared Preferences。

來源

2011-05-02 18:42:35

JSON的網址不工作

回答

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