如何在AsyncTask中執行函數？

Question

我必須在AsyncTask中使用directions（）函數來避免UI線程上的網絡處理。我無法做到這一點。 我的代碼是

public class MainActivity extends MapActivity { 

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

     MapView mapView = (MapView) findViewById(R.id.mapview); //or you can declare it directly with the API key 
     Route route = directions(new GeoPoint((int)(26.2*1E6),(int)(50.6*1E6)), new GeoPoint((int)(26.3*1E6),(int)(50.7*1E6))); 
     RouteOverlay routeOverlay = new RouteOverlay(route, Color.BLUE); 
     mapView.getOverlays().add(routeOverlay); 
     mapView.invalidate(); 
    } 

    private Route directions(final GeoPoint start, final GeoPoint dest) { 
     Parser parser; 
     //https://developers.google.com/maps/documentation/directions/#JSON <- get api 
     String jsonURL = "http://maps.googleapis.com/maps/api/directions/json?"; 
     final StringBuffer sBuf = new StringBuffer(jsonURL); 
     sBuf.append("origin="); 
     sBuf.append(start.getLatitudeE6()/1E6); 
     sBuf.append(','); 
     sBuf.append(start.getLongitudeE6()/1E6); 
     sBuf.append("&destination="); 
     sBuf.append(dest.getLatitudeE6()/1E6); 
     sBuf.append(','); 
     sBuf.append(dest.getLongitudeE6()/1E6); 
     sBuf.append("&sensor=true&mode=driving"); 
     parser = new GoogleParser(sBuf.toString()); 
     Route r = parser.parse(); 
     return r; 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.activity_main, menu); 
     return true; 
    } 

    @Override 
    protected boolean isRouteDisplayed() { 
     // TODO Auto-generated method stub 
     return false; 
    } 

} 

Answer 1

也許這樣？

public class MainActivity extends MapActivity { 

    private MapView mapView; 

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

     mapView = (MapView) findViewById(R.id.mapview); //or you can declare it directly with the API key 
     // You can execute it at onCreate or whenever you want, for example: in a click event 
     new AsyncRoutes().execute(); 
    } 

    private Route directions(final GeoPoint start, final GeoPoint dest) { 
     Parser parser; 
     //https://developers.google.com/maps/documentation/directions/#JSON <- get api 
     String jsonURL = "http://maps.googleapis.com/maps/api/directions/json?"; 
     final StringBuffer sBuf = new StringBuffer(jsonURL); 
     sBuf.append("origin="); 
     sBuf.append(start.getLatitudeE6()/1E6); 
     sBuf.append(','); 
     sBuf.append(start.getLongitudeE6()/1E6); 
     sBuf.append("&destination="); 
     sBuf.append(dest.getLatitudeE6()/1E6); 
     sBuf.append(','); 
     sBuf.append(dest.getLongitudeE6()/1E6); 
     sBuf.append("&sensor=true&mode=driving"); 
     parser = new GoogleParser(sBuf.toString()); 
     Route r = parser.parse(); 
     return r; 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.activity_main, menu); 
     return true; 
    } 

    @Override 
    protected boolean isRouteDisplayed() { 
     // TODO Auto-generated method stub 
     return false; 
    } 

    private class AsyncRoutes extends AsyncTask<Void, Integer, Route> { 

     private ProgressDialog pDialog; 

     @Override 
     protected void onPreExecute() { 

      pDialog = new ProgressDialog(LoginActivity.this); 
      pDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER); 
      pDialog.setMessage("Obtaining routes..."); 
      pDialog.setCancelable(false); 
      pDialog.show(); 
     } 

     @Override 
     protected Route doInBackground(Void... params) { 

      Route route = directions(new GeoPoint((int)(26.2*1E6),(int)(50.6*1E6)), new GeoPoint((int)(26.3*1E6),(int)(50.7*1E6))); 
      return route; 
     } 

     @Override 
     protected void onPostExecute(Route route) {   

      RouteOverlay routeOverlay = new RouteOverlay(route, Color.BLUE); 
      mapView.getOverlays().add(routeOverlay); 
      mapView.invalidate(); 

      pDialog.dismiss(); 
     } 
    } 

} 

Answer 2

這是一個AsyncTask

public class TalkToServer extends AsyncTask<String, String, String> { 
    @Override 
    protected void onPreExecute() { 
     super.onPreExecute(); 
    } 

    @Override 
    protected void onProgressUpdate(String... values) { 
     super.onProgressUpdate(values); 

    } 

    @Override 
    protected String doInBackground(String... params) { 
    //do your work here 
     return something; 
    } 

    @Override 
    protected void onPostExecute(String result) { 
     super.onPostExecute(result); 
      // do something with data here-display it or send to mainactivity 
} 

的基本結構，你可以做你的網絡的東西和/或東西，你在doInBackground()在directions和更新其他方法UI。你也可以把directions方法的私有方法您AsyncTask

那麼你會從你的MainActivity稱此像

TalkToServer networkStuff = new TalkToServer(); //could pass params to a constructor here such as context 
networkStuff.execute(); 

如果AsyncTask不是一個內部類的MainActivity，那麼你就需要構造函數從您的MainActivity收到背景下，如果你想要做的東西UI

Answer 3

這裏是什麼，我認爲他們的意思時，他們說，你可以使用的AsyncTask：

public class MainActivity extends MapActivity { 

private MapView mapView; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    mapView = (MapView) findViewById(R.id.mapview); //or you can declare it directly with the API key 
    RouteTask routeTask = new RouteTask(new GeoPoint((int)(26.2*1E6),(int)(50.6*1E6)), new GeoPoint((int)(26.3*1E6),(int)(50.7*1E6)); 
    routeTask.execute(""); 
} 

private Route directions(final GeoPoint start, final GeoPoint dest) { 
    Parser parser; 
    //https://developers.google.com/maps/documentation/directions/#JSON <- get api 
    String jsonURL = "http://maps.googleapis.com/maps/api/directions/json?"; 
    final StringBuffer sBuf = new StringBuffer(jsonURL); 
    sBuf.append("origin="); 
    sBuf.append(start.getLatitudeE6()/1E6); 
    sBuf.append(','); 
    sBuf.append(start.getLongitudeE6()/1E6); 
    sBuf.append("&destination="); 
    sBuf.append(dest.getLatitudeE6()/1E6); 
    sBuf.append(','); 
    sBuf.append(dest.getLongitudeE6()/1E6); 
    sBuf.append("&sensor=true&mode=driving"); 
    parser = new GoogleParser(sBuf.toString()); 
    Route r = parser.parse(); 
    return r; 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.activity_main, menu); 
    return true; 
} 

@Override 
protected boolean isRouteDisplayed() { 
    // TODO Auto-generated method stub 
    return false; 
} 

class RouteTask extends AsyncTask<String, Void, String> { 
    private GeoPoint start; 
    private GeoPoint dest; 
    private Route route; 

    public RouteTask(GeoPoint start, GeoPoint dest) { 
     this.start = start; 
     this.dest = dest; 
    } 

    protected String doInBackground(String... strings) { 
     //runs the directions method in a background thread. 
     route = directions(start, dest); 
     return "Started"; 
    } 

    @Override 
    protected void onPostExecute(String s) { 
     //Updates the UI on the main/UI thread (post execute is called on the main/UI thread). 
     RouteOverlay routeOverlay = new RouteOverlay(route, Color.BLUE); 
     mapView.getOverlays().add(routeOverlay); 
     mapView.invalidate(); 
    } 
} 

}

這將運行在後臺線程的方向的方法和更新主/ UI線程在地圖上。作爲所有編程語言的一般練習，您應該在繪製到屏幕的線程（本例中爲主/ UI線程）上執行UI工作。

這應該做你所需要的。