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Android我如何通過意圖將變量從選項卡傳遞到活動

2012-10-22 56 views
0

對不起，我是新來的android和自我學習它.. 我有一個標籤列表，我用來循環..所有的標籤是鏈接到同一個活動，但只需要通過一些不同的URL僅用於數據.. 我已經嘗試了很多辦法像Android我如何通過意圖將變量從選項卡傳遞到活動

TabSpec page = tabHost.newTabSpec(title); 
       Intent pageIntent = new Intent(this, mainpage.class); 
       pageIntent.putExtra("url", url); 
       page.setIndicator(title); 
       page.setContent(pageIntent);

和

String text = getIntent().getStringExtra("url");

獲得的價值，但它不運作良好， logcat有很多錯誤..

從logcat的

這裏我的標籤代碼..

for(int i = 0; i < category.length(); i++){ 
       JSONObject c = category.getJSONObject(i); 

       String title = c.getString(TAG_TITLE); 
       String url = "http://www.abcde.com.my/list3.php?json&"+c.getString(TAG_URL); 

       TabSpec page = tabHost.newTabSpec(title); 
       Intent pageIntent = new Intent(this, mainpage.class); 
       pageIntent.putExtra("url", url); 
       page.setIndicator(title); 
       page.setContent(pageIntent); 


       tabHost.addTab(page); 
      }

這裏的代碼，活動...

String text = getIntent().getStringExtra("url"); 
    private String url = text;

錯誤代碼

10-22 02:14:24.313: E/AndroidRuntime(1660): FATAL EXCEPTION: main 
10-22 02:14:24.313: E/AndroidRuntime(1660): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.androidhive.jsonparsing/com.androidhive.jsonparsing.kwongwahtab}: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.androidhive.jsonparsing/com.androidhive.jsonparsing.mainpage}: java.lang.NullPointerException 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.os.Handler.dispatchMessage(Handler.java:99) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.os.Looper.loop(Looper.java:123) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at java.lang.reflect.Method.invokeNative(Native Method) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at java.lang.reflect.Method.invoke(Method.java:507) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at dalvik.system.NativeStart.main(Native Method) 
10-22 02:14:24.313: E/AndroidRuntime(1660): Caused by: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.androidhive.jsonparsing/com.androidhive.jsonparsing.mainpage}: java.lang.NullPointerException 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.ActivityThread.startActivityNow(ActivityThread.java:1487) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:654) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.widget.TabHost.setCurrentTab(TabHost.java:326) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.widget.TabHost.addTab(TabHost.java:216) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at com.androidhive.jsonparsing.kwongwahtab.onCreate(kwongwahtab.java:55) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  ... 11 more 
10-22 02:14:24.313: E/AndroidRuntime(1660): Caused by: java.lang.NullPointerException 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at com.androidhive.jsonparsing.mainpage.<init>(mainpage.java:25) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at java.lang.Class.newInstanceImpl(Native Method) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at java.lang.Class.newInstance(Class.java:1409) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.Instrumentation.newActivity(Instrumentation.java:1021) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1561) 
10-22 02:14:24.313: E/AndroidRuntime(1660):  ... 20 more

任何一個能幫助我那？ 這裏是我的標籤活動

package com.androidhive.jsonparsing; 

import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 

import android.app.TabActivity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.widget.TabHost; 
import android.widget.TabHost.TabSpec; 

@SuppressWarnings("deprecation") 
public class kwongwahtab extends TabActivity { 
    /** Called when the activity is first created. */ 
    private static String url = "http://www.kwongwah.com.my/channels2.plist"; 
    private static final String TAG_CATEGORY = "categorylist"; 
    private static final String TAG_TITLE = "title"; 
    private static final String TAG_URL = "url"; 
    public static String url2; 
    JSONArray category = null; 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 

     TabHost tabHost = getTabHost(); 

     // Creating JSON Parser instance 
     JSONParser jParser = new JSONParser(); 

     // getting JSON string from URL 
     JSONObject json = jParser.getJSONFromUrl(url); 

     try { 
      // Getting Array of Contacts 
      category = json.getJSONArray(TAG_CATEGORY); 

      // looping through All Contacts 
      for(int i = 0; i < category.length(); i++){ 
       JSONObject c = category.getJSONObject(i); 

       // Storing each json item in variable 

       String title = c.getString(TAG_TITLE); 
       String url = "http://www.kwongwah.com.my/plist3.php?json&"+c.getString(TAG_URL); 

       TabSpec page = tabHost.newTabSpec(title); 
       Intent pageIntent = new Intent(this, mainpage.class); 
       pageIntent.putExtra("url", url); 
       page.setIndicator(title); 
       page.setContent(pageIntent); 


       tabHost.addTab(page); 
      } 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 

    } 
}

mainpage.java 包com.androidhive.jsonparsing;

import java.util.ArrayList; 
import java.util.HashMap; 

import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 

import android.app.ListActivity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemClickListener; 
import android.widget.ListAdapter; 
import android.widget.ListView; 
import android.widget.SimpleAdapter; 
import android.widget.TextView; 

public class mainpage extends ListActivity { 

    // url to make request 
    String text = getIntent().getStringExtra("url"); 
    private String url = text; 


    // JSON Node names 
    private static final String TAG_CONTACTS = "new_list"; 

    private static final String TAG_SUBJECT = "subject"; 
    private static final String TAG_HTML = "html"; 
    private static final String TAG_ADDED = "added"; 

    // contacts JSONArray 
    JSONArray contacts = null; 

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

     // Hashmap for ListView 
     ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>(); 

     // Creating JSON Parser instance 
     JSONParser jParser = new JSONParser(); 

     // getting JSON string from URL 
     JSONObject json = jParser.getJSONFromUrl(url); 

     try { 
      // Getting Array of Contacts 
      contacts = json.getJSONArray(TAG_CONTACTS); 

      // looping through All Contacts 
      for(int i = 0; i < contacts.length(); i++){ 
       JSONObject c = contacts.getJSONObject(i); 

       // Storing each json item in variable 

       String subject = c.getString(TAG_SUBJECT); 
       //String html = "<img src='http://www.kwongwah.com.my/news/2012/10/18/32_1.jpg'>"; 
       String html = c.getString(TAG_HTML); 
       String added = c.getString(TAG_ADDED); 

       // Phone number is agin JSON Object 


       // creating new HashMap 
       HashMap<String, String> map = new HashMap<String, String>(); 

       // adding each child node to HashMap key => value 

       map.put(TAG_SUBJECT, subject); 
       map.put(TAG_HTML, html); 
       map.put(TAG_ADDED, added); 

       // adding HashList to ArrayList 
       contactList.add(map); 
      } 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 


     /** 
     * Updating parsed JSON data into ListView 
     * */ 
     ListAdapter adapter = new SimpleAdapter(this, contactList, 
       R.layout.list_item, 
       new String[] { TAG_SUBJECT, TAG_HTML, TAG_ADDED }, new int[] { 
         R.id.subject, R.id.html, R.id.added}); 

     setListAdapter(adapter); 

     // selecting single ListView item 
     ListView lv = getListView(); 

     // Launching new screen on Selecting Single ListItem 
     lv.setOnItemClickListener(new OnItemClickListener() { 

      public void onItemClick(AdapterView<?> parent, View view, 
        int position, long id) { 
       // getting values from selected ListItem 
       String subject = ((TextView) view.findViewById(R.id.subject)).getText().toString(); 
       String html = ((TextView) view.findViewById(R.id.html)).getText().toString(); 
       String added = ((TextView) view.findViewById(R.id.added)).getText().toString(); 

       // Starting new intent 
       Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class); 
       in.putExtra(TAG_SUBJECT, subject); 
       in.putExtra(TAG_HTML, html); 
       in.putExtra(TAG_ADDED, added); 

       startActivity(in); 

      } 
     }); 



    } 

}

來源

2012-10-22 Ryano Ccg

+0

什麼是，mainpage.java:25 –

+0

@GregGiacovelli私人字符串URL =文本; –

+0

我有一種感覺，你正在運行的代碼不是你想象的代碼。兩個變量之間的賦值不會導致NullPointerException。不管怎樣，你如何驗證網址沒有被正確發送？你的構造函數似乎有代碼，你可以粘貼它嗎？ –

回答

0

這就是問題所在。在聲明成員變量的位置您不能引用getIntent()方法。它會在類的構造函數中隱式調用。構造函數將在活動每次綁定到Context或給定意圖之前發生。

public class mainpage extends ListActivity { 

    // url to make request ... -- This will only be valid from onCreate() to onDestroy() 
    String text = getIntent().getStringExtra("url");

移動這種類型的代碼的生命週期方法，像onCreate()：

public class mainpage extends ListActivity { 

    // url to make request 
    String text; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     // At this point the Context is bound and the Intent is set on it. 
     text = getIntent().getStringExtra("url"); 
     setContentView(R.layout.layout); 

     // Hashmap for ListView 
     ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>(); 

     // Creating JSON Parser instance 
     JSONParser jParser = new JSONParser();

來源

2012-10-22 09:25:08

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