在Android中控制標題欄進度條時​​出現問題

Question

我正在創建一個應用程序，它有4個選項卡，顯示來自網站的4個不同的提要。我想要做的是在用戶每次點擊標籤時在自定義標題欄中顯示進度條，然後在完成加載後隱藏進度條。

這裏是我的標題欄佈局：

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout android:id="@+id/titlebar" 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="horizontal" 
    android:layout_height="30dip" 
    android:layout_width="fill_parent" 
    android:gravity="center_vertical" 
    android:padding="0dip" 
    android:background="#055843"> 
    <TextView 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/title" 
    android:text="TheGangGreen" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:textColor="#ffffff" 
    android:layout_marginLeft="5dp" 
    android:layout_marginTop="4dp" 
    android:textStyle="bold" /> 
    <ProgressBar 
    android:id="@+id/progress_bar" style="?android:attr/progressBarStyleSmall" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_centerVertical="true" 
    android:layout_alignParentRight="true" 
    android:layout_marginRight="5dp" /> 
</RelativeLayout> 

主類：

public class Main extends TabActivity { 
    private static final String TAG = "MyActivity"; 
    ProgressBar titleProgressBar; 
    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     requestWindowFeature(Window.FEATURE_CUSTOM_TITLE); 
     setContentView(R.layout.main); 
     getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.titlebar); 
     titleProgressBar = (ProgressBar) findViewById(R.id.progress_bar); 
     titleProgressBar.setVisibility(ProgressBar.GONE); 

     //tab related stuff goes here 
    } 

    Handler progressHandle = new Handler(){ 
     public void handleMessage(Message msg){ 
      Log.d(TAG, "message = " + msg.arg1); 
      if(msg.arg1 == 1){ // show progress 
       showProgressBar(); 
      } 
      else { 
       hideProgressBar(); 
      } 
     } 
    }; 

    public void showProgressBar(){ 
      Log.d(TAG, "show progress bar"); 
     titleProgressBar.setVisibility(ProgressBar.VISIBLE); 
    } 
} 

標籤的一類：

public class NewsTab extends Activity { 
    private static final String TAG = "MyActivity"; 
    private static final String newsURL = "http://blahblah"; 
    ListView newsList; 
    FeedAdapter arrayAdapter; 
    ArrayList<news> news = null; 
    Main main; 

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

     newsList = (ListView)findViewById(R.id.news_list); 

     news = new ArrayList<news>(); 

     arrayAdapter = new FeedAdapter(NewsTab.this, R.layout.news_item, news); 
     newsList.setAdapter(arrayAdapter); 
     main = new Main(); 
     new GetFeedTask().execute(this.newsURL); 
    } 

    private class GetFeedTask extends AsyncTask<String, String, String> { 
     @Override 
     protected String doInBackground(String... urls) { 
      // TODO Auto-generated method stub 
      Random randomizer = new Random(System.currentTimeMillis()); 
      String responseBody = ""; 
      try { 
       URL feedUrl = new URL(urls[0] + "?" + randomizer.nextInt(10000)); 
       URLConnection tc = feedUrl.openConnection(); 
       BufferedReader in = new BufferedReader(new InputStreamReader(tc.getInputStream())); 
       String line; 

       while ((line = in.readLine()) != null) { 
        responseBody += line; 
       } 
      } catch (MalformedURLException e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } catch (IOException e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
      return responseBody; 
     } 

     protected void onPreExecute(){ 
      Message msg = new Message(); 
      msg.arg1 = 1; 
      main.progressHandle.sendMessage(msg); 
     } 

     protected void onPostExecute(String response) { 
      try { 
       Type collectionType = new TypeToken<ArrayList<news>>(){}.getType(); 
       List<news> lst = new Gson().fromJson(response, collectionType); 
       Message msg = new Message(); 
       msg.arg1 = 2; 
       main.progressHandle.sendMessage(msg); 
       news.clear(); // clear the adapter array so an updated list won't be appended to the existing one 
       for(news l : lst) 
       { 
        news.add(l); 
       } 
       arrayAdapter.notifyDataSetChanged(); 
      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
     } 


    } 
} 

那麼，是正確發送從onPreExecute消息，但titleProgressBar.setVisibility（ProgressBar.VISIBLE）;在showProgressBar中導致NullPointerException。

謝謝

，這裏是我的logcat：

D/AndroidRuntime( 423): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<< 

D/AndroidRuntime( 423): CheckJNI is ON 

D/AndroidRuntime( 423): --- registering native functions --- 

I/ActivityManager( 59): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.tgg.test/.SplashScreen } 

D/AndroidRuntime( 423): Shutting down VM 

D/dalvikvm( 423): Debugger has detached; object registry had 1 entries 

I/ActivityManager( 59): Start proc com.tgg.test for activity com.tgg.test/.SplashScreen: pid=430 uid=10047 gids={3003} 

I/AndroidRuntime( 423): NOTE: attach of thread 'Binder Thread #3' failed 

I/ActivityManager( 59): Displayed activity com.tgg.test/.SplashScreen: 1725 ms (total 420542 ms) 

I/ActivityManager( 59): Starting activity: Intent { cmp=com.tgg.test/.Main } 

D/MyActivity( 430): resume 

D/MyActivity( 430): message = 1 

D/AndroidRuntime( 430): Shutting down VM 

W/dalvikvm( 430): threadid=1: thread exiting with uncaught exception (group=0x4001d800) 

E/AndroidRuntime( 430): FATAL EXCEPTION: main 

E/AndroidRuntime( 430): java.lang.NullPointerException 

E/AndroidRuntime( 430): at com.tgg.test.Main.showProgressBar(Main.java:76) 

E/AndroidRuntime( 430): at com.tgg.test.Main$1.handleMessage(Main.java:67) 

E/AndroidRuntime( 430): at android.os.Handler.dispatchMessage(Handler.java:99) 

E/AndroidRuntime( 430): at android.os.Looper.loop(Looper.java:123) 

E/AndroidRuntime( 430): at android.app.ActivityThread.main(ActivityThread.java:4627) 

E/AndroidRuntime( 430): at java.lang.reflect.Method.invokeNative(Native Method) 

E/AndroidRuntime( 430): at java.lang.reflect.Method.invoke(Method.java:521) 

E/AndroidRuntime( 430): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 

E/AndroidRuntime( 430): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 

E/AndroidRuntime( 430): at dalvik.system.NativeStart.main(Native Method) 

W/ActivityManager( 59): Force finishing activity com.tgg.test/.Main 

W/ActivityManager( 59): Activity pause timeout for HistoryRecord{450a2a20 com.tgg.test/.Main} 

I/global ( 430): Default buffer size used in BufferedReader constructor. It would be better to be explicit if an 8k-char buffer is required. 

I/Process ( 430): Sending signal. PID: 430 SIG: 9 

I/WindowManager( 59): WIN DEATH: Window{450aa2a8 com.tgg.test/com.tgg.test.SplashScreen paused=true} 

I/ActivityManager( 59): Process com.tgg.test (pid 430) has died. 

Answer 1

在你父母的活動，你做任何事情之前，你需要做的 requestWindowFeature通話，然後在你的孩子的活動，你叫

getParent().setProgressBarIndeterminateVisibility(true/false);