TextView值未被服務更新 - Android GPS

Question

我有一個啓動我的DelayedMessageService的按鈕。該服務是非常簡單的服務，因爲它所做的只是計算用戶行進的距離。我想顯示行進的總距離，但問題是它沒有在我的MainAcitivy的TextView中顯示值。有人可以幫我解決這個問題。這裏是我的MainAcvity，服務和activity_main.xml中：

MainActivity：

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.os.Handler; 
import android.view.View; 
import android.widget.Button; 
import android.widget.TextView; 

public class MainActivity extends Activity { 
    String distanceStr; 

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


     watchMileage(); 



     Button button = (Button) findViewById(R.id.button); 

     button.setOnClickListener(new View.OnClickListener() { 
      public void onClick(View v) { 
       Intent intent = new Intent(MainActivity.this, DelayedMessageService.class); 
       intent.putExtra(DelayedMessageService.EXTRA_MESSAGE, 
         getResources().getString(R.string.button_response)); 
       startService(intent); 
      } 
     }); 
    } 

    private void watchMileage() { 
     final TextView distanceView = (TextView)findViewById(R.id.distance); 
     final Handler handler = new Handler(); 
     handler.post(new Runnable() { 
      @Override 
      public void run() { 
       double distance = 0.0; 
       if (mDelayedMessageService != null) { 
        distance = mDelayedMessageService.getMiles(); 
       } 
       distanceStr = String.format("%1$,.2f miles", distance); 
       distanceView.setText(distanceStr); 
       handler.postDelayed(this, 1000); 
      } 
     }); 
    } 

    //Log.v("INOCRECTEA", distanceStr.toString()); 
} 

// activity_main

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
       xmlns:tools="http://schemas.android.com/tools" 
       android:layout_width="match_parent" 
       android:layout_height="match_parent" 
       android:orientation="vertical" 
       tools:context=".MainActivity"> 

    <Button 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="@string/button_text" 
     android:id="@+id/button" 
     android:onClick="onClick" 
     android:layout_alignParentTop="true" 
     android:layout_centerHorizontal="true" /> 

    <TextView android:text="" 
      android:id="@+id/distance" 
      android:textAppearance="?android:attr/textAppearanceLarge" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:layout_centerHorizontal="true" 
      android:singleLine="false" 
      android:textSize="50sp"/> 
</LinearLayout> 

Answer 1

你聲明的變量稱爲mDelayedMessageService，但我沒有看到你初始化在你提供的代碼片段中，因此它是null。然後裏面watchMileage()你做

if (mDelayedMessageService != null) { 
     distance = mDelayedMessageService.getMiles(); 
} 

顯然，你distance永遠是0.0。