無法訪問另一個

Question

我FirstActivity一個活動的變量，包括該代碼

mHandler.postDelayed(mLaunchTask,10000); 
private Runnable mLaunchTask = new Runnable() 
      { 
       public void run() 
       { 
        Intent i = new Intent(getApplicationContext(),NearestPoint.class); 
        Bundle params = new Bundle(); 
        params.putFloat("latiA", latA); 
        params.putFloat("longiA", longA); 
        params.putFloat("latiB", latB); 
        params.putFloat("longiB", longB); 
        params.putFloat("latiC", latC); 
        params.putFloat("longiC", longC); 
        i.putExtras(params); 
        startActivity(i); 
       } 
      };  

活動NearestPoint包括該代碼

public float latA, longA, latB, longB, latC, longC; 
    Intent it = getIntent(); {   
    if (it != null) 
    { 
     Bundle params = it.getExtras(); 
     if (params != null) 
     { 
      latA = params.getFloat("latiA"); 
      longA = params.getFloat("longiA"); 
      latB = params.getFloat("latiB"); 
      longB = params.getFloat("longiB"); 
      latC = params.getFloat("latiC"); 
      longC = params.getFloat("longiC"); 
     } 
    }} 

我無法訪問拉塔的值，薑黃等在NearestPoint活動中正確。 我試着用吐司顯示：

Toast.makeText(getApplicationContext(),"\nPoint A: \nLatitude: " + latA + "\nLongitude: " + longA, Toast.LENGTH_LONG).show(); 

在FirstActivity它給正確的值，但在NearestPoint我得到0.0的經度和緯度。

這裏是我的清單：

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="com.example.gpsdistance" 
    android:versionCode="1" 
    android:versionName="1.0" > 

    <uses-sdk 
     android:minSdkVersion="8" 
     android:targetSdkVersion="16" /> 

    <application 
     android:allowBackup="true" 
     android:icon="@drawable/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name="com.example.gpsdistance.FirstActivity" 
      android:label="@string/app_name" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
     <activity 
      android:name="com.example.gpsdistance.NearestPoint" 
      android:label="@string/title_activity_nearest_point" > 
     </activity> 
     <activity 
      android:name="com.example.gpsdistance.MinimumDistance" 
      android:label="@string/title_activity_minimum_distance" > 
     </activity> 
    </application> 

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

</manifest> 

這裏是我的完整FirstActivity類：

package com.example.gpsdistance; 

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

public class FirstActivity extends Activity { 

    Button btnShowLocation, btnMinDis; 
    TextView display= null; 
    //private final Context mctx; 
    double latuser; 
    double longuser; 
    double dx1, dy1, delta_long1, delta_lat1, final_long1, final_lat1; 
    double dx2, dy2, delta_long2, delta_lat2, final_long2, final_lat2; 
    double dx3, dy3, delta_long3, delta_lat3, final_long3, final_lat3; 
    public float latA, longA, latB, longB, latC, longC; 
    public String latiA, longiA, latiB, longiB, latiC, longiC ; 
    // GPSTracker class 
    GPSTracker gps; 

    void getGPS() 
    { 
     gps = new GPSTracker(FirstActivity.this); 
    } 

    void points() 
    { 

     latuser = gps.getLatitude(); 
     longuser = gps.getLongitude(); 

     dx1 = 120*Math.cos(35); 
     dy1 = 120*Math.sin(35); 
     delta_long1 = dx1/(111320*Math.cos(latuser)); 
     delta_lat1 = dy1/110540; 
     final_long1 = longuser + delta_long1; 
     final_lat1 = latuser + delta_lat1; 
     dx2 = 150*Math.cos(38); 
     dy2 = 150*Math.sin(38); 
     delta_long2 = dx2/(111320*Math.cos(latuser)); 
     delta_lat2 = dy2/110540; 
     final_long2 = longuser + delta_long2; 
     final_lat2 = latuser + delta_lat2; 
     dx3 = 180*Math.cos(38); 
     dy3 = 180*Math.sin(38); 
     delta_long3 = dx3/(111320*Math.cos(latuser)); 
     delta_lat3 = dy3/110540; 
     final_long3 = longuser + delta_long3; 
     final_lat3 = latuser + delta_lat3; 

     latA= (float)final_lat1; 
     longA= (float)final_long1; 
     latB= (float)final_lat2; 
     longB= (float)final_long2; 
     latC= (float)final_lat3; 
     longC= (float)final_long3; 
    } 

    private float getLatiA() { 
      return this.latA; 
     } 
    /*public FirstActivity(Context ctx) 
    { 
     this.mctx = ctx; 
     getGPS(); 
     points(); 
    } */ 
    private float computeDistance(double lat1, double lon1, 
      double lat2, double lon2) { 
      // Based on http://www.ngs.noaa.gov/PUBS_LIB/inverse.pdf 
      // using the "Inverse Formula" (section 4) 

      int MAXITERS = 20; 
      // Convert lat/long to radians 
      lat1 *= Math.PI/180.0; 
      lat2 *= Math.PI/180.0; 
      lon1 *= Math.PI/180.0; 
      lon2 *= Math.PI/180.0; 

      double a = 6378137.0; // WGS84 major axis 
      double b = 6356752.3142; // WGS84 semi-major axis 
      double f = (a - b)/a; 
      double aSqMinusBSqOverBSq = (a * a - b * b)/(b * b); 

      double L = lon2 - lon1; 
      double A = 0.0; 
      double U1 = Math.atan((1.0 - f) * Math.tan(lat1)); 
      double U2 = Math.atan((1.0 - f) * Math.tan(lat2)); 

      double cosU1 = Math.cos(U1); 
      double cosU2 = Math.cos(U2); 
      double sinU1 = Math.sin(U1); 
      double sinU2 = Math.sin(U2); 
      double cosU1cosU2 = cosU1 * cosU2; 
      double sinU1sinU2 = sinU1 * sinU2; 

      double sigma = 0.0; 
      double deltaSigma = 0.0; 
      double cosSqAlpha = 0.0; 
      double cos2SM = 0.0; 
      double cosSigma = 0.0; 
      double sinSigma = 0.0; 
      double cosLambda = 0.0; 
      double sinLambda = 0.0; 

      double lambda = L; 
      for (int iter = 0; iter < MAXITERS; iter++) { 
       double lambdaOrig = lambda; 
       cosLambda = Math.cos(lambda); 
       sinLambda = Math.sin(lambda); 
       double t1 = cosU2 * sinLambda; 
       double t2 = cosU1 * sinU2 - sinU1 * cosU2 * cosLambda; 
       double sinSqSigma = t1 * t1 + t2 * t2; 
       sinSigma = Math.sqrt(sinSqSigma); 
       cosSigma = sinU1sinU2 + cosU1cosU2 * cosLambda; 
       sigma = Math.atan2(sinSigma, cosSigma); 
       double sinAlpha = (sinSigma == 0) ? 0.0 : 
        cosU1cosU2 * sinLambda/sinSigma; 
       cosSqAlpha = 1.0 - sinAlpha * sinAlpha; 
       cos2SM = (cosSqAlpha == 0) ? 0.0 : 
        cosSigma - 2.0 * sinU1sinU2/cosSqAlpha; 

       double uSquared = cosSqAlpha * aSqMinusBSqOverBSq; 
       A = 1 + (uSquared/16384.0) * 
        (4096.0 + uSquared * 
        (-768 + uSquared * (320.0 - 175.0 * uSquared))); 
       double B = (uSquared/1024.0) * 
        (256.0 + uSquared * 
        (-128.0 + uSquared * (74.0 - 47.0 * uSquared))); 
       double C = (f/16.0) * 
        cosSqAlpha * 
        (4.0 + f * (4.0 - 3.0 * cosSqAlpha)); 
       double cos2SMSq = cos2SM * cos2SM; 
       deltaSigma = B * sinSigma * 
        (cos2SM + (B/4.0) * 
        (cosSigma * (-1.0 + 2.0 * cos2SMSq) - 
         (B/6.0) * cos2SM * 
         (-3.0 + 4.0 * sinSigma * sinSigma) * 
         (-3.0 + 4.0 * cos2SMSq))); 

       lambda = L + 
        (1.0 - C) * f * sinAlpha * 
        (sigma + C * sinSigma * 
        (cos2SM + C * cosSigma * 
         (-1.0 + 2.0 * cos2SM * cos2SM))); 

       double delta = (lambda - lambdaOrig)/lambda; 
       if (Math.abs(delta) < 1.0e-12) { 
        break; 
       } 
      } 

      float distance = (float) (b * A * (sigma - deltaSigma)); 

      return distance; 
    } 

    /*public FirstActivity() 
     { 
      getGPS(); 
      if(gps.canGetLocation()) 
      points(); 
     }*/ 


    @Override 
    protected void onCreate(Bundle savedInstanceState) 
     { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.firstactivity); 
      final LinearLayout lView = new LinearLayout(this); 
      display= new TextView(this); 
      btnMinDis=new Button(this); 
      btnMinDis.setText("Nearest Point"); 
      final Handler mHandler = new Handler(); 
      btnShowLocation = (Button) findViewById(R.id.buttonLocation); 

      btnShowLocation.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View arg0) 
       { 
        // TODO Auto-generated method stub 

        getGPS(); 
        // check if GPS enabled 
        if(gps.canGetLocation()) 
         { 

         points(); 
          float initialdisA = computeDistance(latuser, longuser, latA, longA); 
          float initialdisB = computeDistance(latuser, longuser, latB, longB); 
          float initialdisC = computeDistance(latuser, longuser, latC, longC);   
          Toast.makeText(getApplicationContext(),"Point A: \nLatitude: " + latA + "\nLongitude: " + longA, Toast.LENGTH_LONG).show(); 
          lView.addView(display); 
          setContentView(lView); 
          display.setText("Initial Location is - \nLatitude: " + latuser + " N" + "\nLongitude: " + longuser + " E" 
             + "\n\n\nPoint A:\n" + "Latitude: " + latA + "N" + "\nLongitude: " + longA + "E" 
             + "\nPoint B:\n" + "Latitude: " + latB + "N" + "\nLongitude: " + longB + "E" 
             + "\nPoint C:\n" + "Latitude: " + latC + "N" + "\nLongitude: " + longC + "E" 
             + "\n\n\nInitial Distance A: " + initialdisA + "m" + "\nInitial Distance B: " + initialdisB + "m" + "\nInitial Distance C: " + initialdisC + "m"); 


          mHandler.postDelayed(mLaunchTask,10000); 
         } 
        else 
         { 
        // GPS or Network is not enabled 
        // Ask user to enable GPS/network in settings 
        gps.showSettingsAlert(); 
         } 
       } 

      private Runnable mLaunchTask = new Runnable() 
      { 
       public void run() 
       { 
        Intent i = new Intent(getApplicationContext(),NearestPoint.class); 
        Bundle params = new Bundle(); 
        params.putFloat("latiA", getLatiA()); 
        params.putFloat("longiA", longA); 
        params.putFloat("latiB", latB); 
        params.putFloat("longiB", longB); 
        params.putFloat("latiC", latC); 
        params.putFloat("longiC", longC); 
        i.putExtras(params); 
        startActivity(i); 
       } 
      };  
     }); 
    } 

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

} 

這裏的鏈接到完整的項目： http://www.filedropper.com/gpsdistance

請幫助。

Answer 1

發生這種情況是因爲在您實例化可運行的latA時，longA，latB，longB，latC，longC都是零值。你應該爲每個值使用一個getter，如下所示：

mHandler.postDelayed(mLaunchTask,10000); 
private Runnable mLaunchTask = new Runnable() 
      { 
       public void run() 
       { 
        Intent i = new Intent(getApplicationContext(),NearestPoint.class); 
        Bundle params = new Bundle(); 
        params.putFloat("latiA", getLatiA()); //You should to call a getter here 
        i.putExtras(params); 
        startActivity(i); 
       } 
      };  



//In your class  
private double getLatiA() { 
    return this.latiA; 
} 

Answer 2

我不明白你爲什麼要在另一個線程中運行一個活動。我建議使用服務。 http://developer.android.com/guide/components/services.html