無法修復NullPointer異常

我是一位剛剛完成他的應用程序並正在調試的amatuer程序員;直到應用程序崩潰不問:(。無法修復NullPointer異常

我沒有從lolcat堆棧跟蹤，並在ContextWrapper下面實現了NullPointerError。

@Override 
public PackageManager getPackageManager() { 
    return mBase.getPackageManager(); 
}

但我不能看到一個問題的。該應用代碼如下：

package com.example.denny.myapplication; 

import android.Manifest; 
import android.Manifest.permission; 
import android.app.AlertDialog; 
import android.content.Context; 
import android.content.DialogInterface; 
import android.content.Intent; 
import android.content.pm.PackageManager; 
import android.location.Location; 
import android.location.LocationManager; 
import android.os.Build; 
import android.os.Bundle; 
import android.os.Handler; 
import android.provider.Settings; 
import android.support.design.widget.FloatingActionButton; 
import android.support.design.widget.Snackbar; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v4.content.ContextCompat; 
import android.support.v7.widget.Toolbar; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 

public class MainActivity extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    PackageManager pm = getPackageManager(); 
    if (pm.checkPermission(permission.ACCESS_FINE_LOCATION, getPackageName()) == PackageManager.PERMISSION_DENIED) { 
     alertboxGPS(); 
    } 
    mHandler = new Handler(); 
    startRepeatingTask(); 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 
    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
    fab.setOnClickListener(new View.OnClickListener() { 
           @Override 
           public void onClick(View view) { 
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG) 
              .setAction("Action", null).show(); 

           } 
          } 

    ); 
    getSystemService(Context.LOCATION_SERVICE); 

} 


@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    getMenuInflater().inflate(R.menu.menu_main, menu); 
    return true; 
} 

@Override 
public PackageManager getPackageManager() { 
    return super.getPackageManager(); 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 

    //Also, chuck the subroutine settings here. :3 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 

PackageManager pm = getPackageManager(); 

protected void alertboxGPS() { 
    AlertDialog.Builder builder = new AlertDialog.Builder(this); 
    builder.setMessage("Your Device's GPS is Disabled") 
      .setCancelable(true) 
      .setTitle("** Gps Status **") 
      .setPositiveButton("Gps On", 
        new DialogInterface.OnClickListener() { 
         public void onClick(DialogInterface dialog, int id) { 
          // finish the current activity 
          // AlertBoxAdvance.this.finish(); 
          Intent myIntent = new Intent(
            Settings.ACTION_SECURITY_SETTINGS); 
          startActivity(myIntent); 
          dialog.cancel(); 
         } 
        }) 
      .setNegativeButton("Cancel", 
        new DialogInterface.OnClickListener() { 
         public void onClick(DialogInterface dialog, int id) { 
          // cancel the dialog box 
          dialog.cancel(); 
         } 
        }); 
    AlertDialog alert = builder.create(); 
    alert.show(); 
} 

protected void alertboxViolation() { 
    AlertDialog.Builder builder = new AlertDialog.Builder(this); 
    builder.setMessage("Please stop walking. You may get in an accident.") 
      .setCancelable(false) 
      .setTitle("Walking Warning") 
      .setPositiveButton("Stop Walking", 
        new DialogInterface.OnClickListener() { 
         public void onClick(DialogInterface dialog, int id) { 
          // finish the current activity 
          // AlertBoxAdvance.this.finish(); 
          Intent myIntent = new Intent(
            Settings.ACTION_SECURITY_SETTINGS); 
          startActivity(myIntent); 
          dialog.cancel(); 
         } 
        }) 
      .setNegativeButton("Cancel", 
        new DialogInterface.OnClickListener() { 
         public void onClick(DialogInterface dialog, int id) { 
          // cancel the dialog box 
          dialog.cancel(); 
         } 
        }); 
    AlertDialog alert = builder.create(); 
    alert.show(); 
} 

protected void alertboxGranted() { 
    AlertDialog.Builder builder = new AlertDialog.Builder(this); 
    builder.setMessage("Access Granted") 
      .setCancelable(true) 
      .setTitle("Access to GPS") 
      .setPositiveButton("Ok", 
        new DialogInterface.OnClickListener() { 
         public void onClick(DialogInterface dialog, int id) { 
          // finish the current activity 
          // AlertBoxAdvance.this.finish(); 
          Intent myIntent = new Intent(
            Settings.ACTION_SECURITY_SETTINGS); 
          startActivity(myIntent); 
          dialog.cancel(); 
         } 
        }) 
      .setNegativeButton("Cancel", 
        new DialogInterface.OnClickListener() { 
         public void onClick(DialogInterface dialog, int id) { 
          // cancel the dialog box 
          dialog.cancel(); 
         } 
        }); 
    AlertDialog alert = builder.create(); 
    alert.show(); 
} 

//Some Default Integers 
int ViolationLimit = 10; 
int SpeedLimit = 100; 
int ExceedInstance = 0; 

//Default Value 
LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 
Location location1; 
Location location2; 

private boolean canGetLocation() { 
    return(ContextCompat.checkSelfPermission(this, 
      Manifest.permission.ACCESS_FINE_LOCATION)== 
      PackageManager.PERMISSION_GRANTED); 
} 

private double GetSpeed(Location location1, Location location2) { 

    if (location1 == null) { 

     location1 = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER); 
     location2 = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER); 
    } else { 
     location1 = location2; 

     } 
      if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)== PackageManager.PERMISSION_GRANTED) { 
       alertboxGranted(); 
     } 
     location2 = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER); 

    double Distance; 
    Distance = location1.distanceTo(location2); 
    double Speed = Distance/mInterval; 
    return Speed; 
} 


private int Judge(double Speed, int ViolationLimit, int SpeedLimit, int ExceedInstance) { 
    if (Speed >= 1 && Speed <= SpeedLimit) { 
     ExceedInstance += 1; 
    } 

    if (ExceedInstance >= ViolationLimit) { 
     alertboxViolation(); 
    } 
    return ExceedInstance; 
} 

void stopRepeatingTask() { 
    mHandler.removeCallbacks(mStatusChecker); 
} 

private int mInterval = 3000; // 3 seconds by default, can be changed later 
private Handler mHandler; 
Runnable mStatusChecker = new Runnable() { 
    @Override 
    public void run() { 
     updateStatus(); 
     mHandler.postDelayed(mStatusChecker, mInterval); 
    } 
}; 

private void updateStatus() { 
    //Is used for updating mInterval 
} 

void startRepeatingTask() { 
    double Speed = GetSpeed(location1, location2); 
    Judge(Speed, ViolationLimit, SpeedLimit, ExceedInstance); 
    mStatusChecker.run(); 
}

}

Lolcat：

10-17 10:41:39.663 7874-7874/com.example.denny.myapplication D/AndroidRuntime: Shutting down VM 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x41967898) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime: FATAL EXCEPTION: main 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.denny.myapplication/com.example.denny.myapplication.MainActivity}: java.lang.NullPointerException 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2219) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread.access$700(ActivityThread.java:159) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:99) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:137) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5419) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at java.lang.reflect.Method.invokeNative(Native Method) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:525) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at dalvik.system.NativeStart.main(Native Method) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime: Caused by: java.lang.NullPointerException 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.content.ContextWrapper.getPackageManager(ContextWrapper.java:94) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at com.example.denny.myapplication.MainActivity.getPackageManager(MainActivity.java:63) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at com.example.denny.myapplication.MainActivity.<init>(MainActivity.java:83) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at java.lang.Class.newInstanceImpl(Native Method) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at java.lang.Class.newInstance(Class.java:1130) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.Instrumentation.newActivity(Instrumentation.java:1078) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2210) 
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread.access$700(ActivityThread.java:159)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:99)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:137)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5419)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at java.lang.reflect.Method.invokeNative(Native Method)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:525)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)  
10-17 10:41:39.663 7874-7874/com.example.denny.myapplication E/AndroidRuntime:  at dalvik.system.NativeStart.main(Native Method)  
10-17 10:41:42.556 7874-7874/com.example.denny.myapplication I/Process: Sending signal. PID: 7874 SIG: 9

我的代碼有什麼問題？

來源

2015-10-16 ForceFieldsForDoors

可以添加崩潰ASLO你的堆棧跟蹤？ – dex

發佈請你的堆棧跟蹤 –

「lolcat」真的應該如何命名:) – bofredo

從我所看到的情況來看，當您的方法startRepeatingTask()未初始化時，您可能會調用location1和location2。他們需要被初始化並且處理一個空例外，就像你在getspeed中那樣。

Location location1 = null; 
Location location2 = null; 

/.../ 

private double GetSpeed(Location location1, Location location2) { 

    if (location1 == null) { 

     location1 = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER); 
     location2 = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER); 
    } else { 
     location1 = location2; 
    } 

/.../ 


void startRepeatingTask() { 
    if (location1 != null && location2 != null) { 
     /.../ 
     double Speed = GetSpeed(location1, location2); 
     Judge(Speed, ViolationLimit, SpeedLimit, ExceedInstance); 
     mStatusChecker.run(); 
}

看到您的堆棧跟蹤後：
空指針異常顯示在你使用過兩行了：

PackageManager pm = getPackageManager();

首先：聲明PackageManager pm;一旦在類範圍和然後將其初始化爲您的 onCreate。

pm= getPackageManager();

通過你的Activity類中和你的onCreate內聲明PackckageManager PM = getPackageManager（），你是否意識到你是在處理兩個獨立的情況下，具有相同的名稱和您的應用程序中不同的範圍。

我很困惑你的代碼，是完全誠實的。

所以我建議以下除了我上面已經說過，你需要研究和嘗試，並瞭解以下內容：

範圍
正在初始化對象 - >調用一個未初始化的對象會導致一個NullPointerException 。
軟件包管理器

這將真正幫助您的進步。在這個網站中很難解釋所有這些。所以我提供了一些鏈接去跟每個點。

來源

2015-10-16 12:50:34

它仍然與空指針。錯誤是因爲我沒有將位置導入startRepeatingTask？ – ForceFieldsForDoors

你已經做了一些藍調。你正在聲明PackageManager兩次。你需要將它聲明爲一個類變量，PackageManager pm;然後在你的創建中初始化它。你根本沒有初始化你的位置。我不確定你在做什麼你的覆蓋getpacakgeManager –

謝謝，我會記住這些。對不起，如果我的代碼混亂。我被時間緊迫;這是我的第一個應用程序。下次我會努力做得更好。 – ForceFieldsForDoors

無法修復NullPointer異常

回答

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