使用構造函數調用方法

我想使用調用方法points()的構造函數。該方法計算3點的經度和緯度。我需要這些值在另一個類。因此，我試圖在構造函數中調用該方法。請幫我一下這個語法。使用構造函數調用方法

這是我的課FirstActivity

package com.example.gpsdistance; 

import android.os.Bundle; 
import android.os.Handler; 
import android.app.Activity; 
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; 
    public float check= 5; 

    //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, lati1; 
    // GPSTracker class 
    GPSTracker gps; 


    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 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; // initial guess 
      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; // (14) 
       sinSigma = Math.sqrt(sinSqSigma); 
       cosSigma = sinU1sinU2 + cosU1cosU2 * cosLambda; // (15) 
       sigma = Math.atan2(sinSigma, cosSigma); // (16) 
       double sinAlpha = (sinSigma == 0) ? 0.0 : 
        cosU1cosU2 * sinLambda/sinSigma; // (17) 
       cosSqAlpha = 1.0 - sinAlpha * sinAlpha; 
       cos2SM = (cosSqAlpha == 0) ? 0.0 : 
        cosSigma - 2.0 * sinU1sinU2/cosSqAlpha; // (18) 

       double uSquared = cosSqAlpha * aSqMinusBSqOverBSq; // defn 
       A = 1 + (uSquared/16384.0) * // (3) 
        (4096.0 + uSquared * 
        (-768 + uSquared * (320.0 - 175.0 * uSquared))); 
       double B = (uSquared/1024.0) * // (4) 
        (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)); // (10) 
       double cos2SMSq = cos2SM * cos2SM; 
       deltaSigma = B * sinSigma * // (6) 
        (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))); // (11) 

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

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

      return distance; 
    } 

    FirstActivity() 
     { 

      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 

        // create class object 
        gps = new GPSTracker(FirstActivity.this); 

        // 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(),"\nLatitude: " + latA , 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); 
        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; 
    } 

}

我試圖使用這些：

1）

FirstActivity() 
{ 
    points(); 
}

2）

FirstActivity(Context context) 
{ 
this.mContext = context; 
    points(); 
}

我既得到錯誤：「應用程序停止PED工作......」

這裏是我的logcat：

01-19 10:12:40.488: D/dalvikvm(608): newInstance failed: Lcom/example/gpsdistance/FirstActivity;.<init>() not accessible to Landroid/app/Instrumentation; 
01-19 10:12:40.538: D/AndroidRuntime(608): Shutting down VM 
01-19 10:12:40.578: W/dalvikvm(608): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
01-19 10:12:40.688: E/AndroidRuntime(608): FATAL EXCEPTION: main 
01-19 10:12:40.688: E/AndroidRuntime(608): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.gpsdistance/com.example.gpsdistance.FirstActivity}: java.lang.IllegalAccessException: access to constructor not allowed 
01-19 10:12:40.688: E/AndroidRuntime(608): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569) 
01-19 10:12:40.688: E/AndroidRuntime(608): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
01-19 10:12:40.688: E/AndroidRuntime(608): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
01-19 10:12:40.688: E/AndroidRuntime(608): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
01-19 10:12:40.688: E/AndroidRuntime(608): at android.os.Handler.dispatchMessage(Handler.java:99) 
01-19 10:12:40.688: E/AndroidRuntime(608): at android.os.Looper.loop(Looper.java:123) 
01-19 10:12:40.688: E/AndroidRuntime(608): at android.app.ActivityThread.main(ActivityThread.java:3683) 
01-19 10:12:40.688: E/AndroidRuntime(608): at java.lang.reflect.Method.invokeNative(Native Method) 
01-19 10:12:40.688: E/AndroidRuntime(608): at java.lang.reflect.Method.invoke(Method.java:507) 
01-19 10:12:40.688: E/AndroidRuntime(608): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
01-19 10:12:40.688: E/AndroidRuntime(608): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
01-19 10:12:40.688: E/AndroidRuntime(608): at dalvik.system.NativeStart.main(Native Method) 
01-19 10:12:40.688: E/AndroidRuntime(608): Caused by: java.lang.IllegalAccessException: access to constructor not allowed 
01-19 10:12:40.688: E/AndroidRuntime(608): at java.lang.Class.newInstanceImpl(Native Method) 
01-19 10:12:40.688: E/AndroidRuntime(608): at java.lang.Class.newInstance(Class.java:1409) 
01-19 10:12:40.688: E/AndroidRuntime(608): at android.app.Instrumentation.newActivity(Instrumentation.java:1021) 
01-19 10:12:40.688: E/AndroidRuntime(608): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1561) 
01-19 10:12:40.688: E/AndroidRuntime(608): ... 11 more 
01-19 10:12:43.669: I/Process(608): Sending signal. PID: 608 SIG: 9

來源

2013-01-19 phoenix

不通過構造函數初始化活動，它會按照您所看到的那樣失敗。另外，你的繼承是如何建立的？每個Activity都是一個「屏幕」，而不是數據對象（因此沒有構造函數init）。考慮將這些東西移到助手類中。 –

你正在做錯誤的方式，因爲最有可能的GPS實例爲空，並提供logcat stacktrace所有崩潰時 –

我已經發布了我使用構造函數的類的代碼。爲了簡化錯誤，目前我沒有爲變量「latA」設置任何繼承。只需使用類中的構造函數就會給出錯誤。當我刪除構造函數時，事情工作正常。但我真的需要構造函數，因爲我需要在新類的points（）中使用計算的變量。 – phoenix

您的積分函數包含此調用

latuser = gps.getLatitude();

然而， gps變量尚未初始化。只有當用戶按下添加到onCreate事件中的活動的按鈕時，纔會創建gps對象。

創建GPS較早...例如在points()

或創建將在類中使用的gps普通呼叫，而不是一個功能。

function getGPS() { 
    if (gps == null) 
    gps = new GPSTracker(FirstActivity.this); 
    return gps; 
}

來源

2013-01-19 04:55:08 GeorgeVremescu

謝謝喬治！有效！ :) – phoenix

是有可能

class AdapterVersion { 

     AdapterVersion() { 
      show(); 
     } 

     public void show(){ 
      System.out.println("Hello"); 
     } 
    } 

    class AdapterVersionNew { 
     AdapterVersionNew() 
     { 
      AdapterVersion a= new AdapterVersion(); 
     } 
     public void show2(){ 
      System.out.println("Hello2"); 
     } 
    } 


    class test2 { 
     public static void main(String[] args) { 
      AdapterVersionNew q = new AdapterVersionNew(); 
     } 
    }

來源

2013-01-19 04:24:12

此代碼以與問題完全相同的方式調用方法......它解決了什麼問題？ – ApproachingDarknessFish

問題不是由作者正確解釋，這個問題需要解決方案的解釋 –

@ManishNagar：我想我已經嘗試過使用你的建議。但我得到錯誤。 – phoenix

使用構造函數調用方法

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