從啓動畫面導航到下一個畫面的錯誤

Question

我創建啓動畫面到我的android項目，如果我運行它啓動畫面出現一段時間，並顯示強制關閉消息，我該怎麼做導航到下一頁？有什麼建議麼？

public class LoadingScreen extends Activity implements LoadingTaskFinishedListener { 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    // Show the splash screen 
    setContentView(R.layout.activity_loading_screen); 
    // Find the progress bar 
    ProgressBar progressBar = (ProgressBar) findViewById(R.id.Progressbar); 
    // Start your loading 
    new LoadingTask(progressBar, null).execute("www.google.co.uk"); // Pass in whatever you need a url is just an example we don't use it in this tutorial 

} 

// This is the callback for when your async task has finished 
public void onTaskFinished() { 
    completeSplash(); 
} 

private void completeSplash(){ 
    startApp(); 
    finish(); // Don't forget to finish this Splash Activity so the user can't return to it! 
} 

private void startApp() { 
    Intent intent = new Intent(LoadingScreen.this, Rebuix.class); 
    startActivity(intent); 
} 

}

我的清單文件

<uses-sdk 
    android:minSdkVersion="8" 
    android:targetSdkVersion="15" /> 

<uses-permission android:name="android.permission.INTERNET" /> 

<application 
    android:icon="@drawable/rebuix" 
    android:label="@string/app_name" 
    android:theme="@style/AppTheme" > 
    <activity 
     android:name=".LoadingScreen" 
     android:label="@string/title_activity_loading_screen" > 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
    <activity 
     android:name=".Rebuix" 
     android:label="@string/title_activity_rebuix" > 
     <meta-data 
      android:name="android.support.PARENT_ACTIVITY" 
      android:value="com.rebuix.com.Rebuix" /> 
    </activity> 
    <activity 
     android:name=".Login" 
     android:label="@string/title_activity_login" > 
     <meta-data 
      android:name="android.support.PARENT_ACTIVITY" 
      android:value="com.rebuix.com.Rebuix" /> 
    </activity> 

logcat的

11-23 13:13:03.798: I/Tutorial(459): Starting task with url: www.google.co.uk 
11-23 13:13:14.156: D/AndroidRuntime(459): Shutting down VM 
11-23 13:13:14.156: W/dalvikvm(459): threadid=1: thread exiting with uncaught exception (group=0x4001d800) 
11-23 13:13:14.166: E/AndroidRuntime(459): FATAL EXCEPTION: main 
11-23 13:13:14.166: E/AndroidRuntime(459): java.lang.NullPointerException 
11-23 13:13:14.166: E/AndroidRuntime(459): at com.rebuix.com.LoadingTask.onPostExecute(LoadingTask.java:68) 
11-23 13:13:14.166: E/AndroidRuntime(459): at com.rebuix.com.LoadingTask.onPostExecute(LoadingTask.java:1) 
11-23 13:13:14.166: E/AndroidRuntime(459): at android.os.AsyncTask.finish(AsyncTask.java:417) 
11-23 13:13:14.166: E/AndroidRuntime(459): at android.os.AsyncTask.access$300(AsyncTask.java:127) 
11-23 13:13:14.166: E/AndroidRuntime(459): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429) 
11-23 13:13:14.166: E/AndroidRuntime(459): at android.os.Handler.dispatchMessage(Handler.java:99) 
11-23 13:13:14.166: E/AndroidRuntime(459): at android.os.Looper.loop(Looper.java:123) 
11-23 13:13:14.166: E/AndroidRuntime(459): at android.app.ActivityThread.main(ActivityThread.java:4627) 
11-23 13:13:14.166: E/AndroidRuntime(459): at java.lang.reflect.Method.invokeNative(Native Method) 
11-23 13:13:14.166: E/AndroidRuntime(459): at java.lang.reflect.Method.invoke(Method.java:521) 
11-23 13:13:14.166: E/AndroidRuntime(459): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
11-23 13:13:14.166: E/AndroidRuntime(459): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
11-23 13:13:14.166: E/AndroidRuntime(459): at dalvik.system.NativeStart.main(Native Method) 

LoadingTask類

public class LoadingTask extends AsyncTask<String, Integer, Integer> { 

public interface LoadingTaskFinishedListener { 
    void onTaskFinished(); // If you want to pass something back to the listener add a param to this method 
} 

// This is the progress bar you want to update while the task is in progress 
private final ProgressBar progressBar; 
// This is the listener that will be told when this task is finished 
private final LoadingTaskFinishedListener finishedListener; 

/** 
* A Loading task that will load some resources that are necessary for the app to start 
* @param progressBar - the progress bar you want to update while the task is in progress 
* @param finishedListener - the listener that will be told when this task is finished 
*/ 
public LoadingTask(ProgressBar progressBar, LoadingTaskFinishedListener finishedListener) { 
    this.progressBar = progressBar; 
    this.finishedListener = finishedListener; 
} 

@Override 
protected Integer doInBackground(String... params) { 
    Log.i("Tutorial", "Starting task with url: "+params[0]); 
    if(resourcesDontAlreadyExist()){ 
     downloadResources(); 
    } 
    // Perhaps you want to return something to your post execute 
    return 1234; 
} 

private boolean resourcesDontAlreadyExist() { 
    // Here you would query your app's internal state to see if this download had been performed before 
    // Perhaps once checked save this in a shared preference for speed of access next time 
    return true; // returning true so we show the splash every time 
} 


private void downloadResources() { 
    // We are just imitating some process thats takes a bit of time (loading of resources/downloading) 
    int count = 10; 
    for (int i = 0; i < count; i++) { 

     // Update the progress bar after every step 
     int progress = (int) ((i/(float) count) * 100); 
     publishProgress(progress); 

     // Do some long loading things 
     try { Thread.sleep(1000); } catch (InterruptedException ignore) {} 
    } 
} 

@Override 
protected void onProgressUpdate(Integer... values) { 
    super.onProgressUpdate(values); 
    progressBar.setProgress(values[0]); // This is ran on the UI thread so it is ok to update our progress bar (a UI view) here 
} 

@Override 
protected void onPostExecute(Integer result) { 
    super.onPostExecute(result); 
    finishedListener.onTaskFinished(); // Tell whoever was listening we have finished 
} 

}

Answer 1

變化

new LoadingTask(progressBar, null).execute("www.google.co.uk"); 

到

new LoadingTask(progressBar, this).execute("www.google.co.uk"); 

我認爲第二個PARAM應該是LoadingTaskFinishedListener。