当试图打开数据库连接传递给webview时，Android应用程序在活动中崩溃

Question

我想开发一个应用程序，它根据微调器值对数据库执行查询，然后将它传递给webview中的下一个意图。出于某种原因，它在该活动中不断崩溃。这里是我的代码：

//import android.R; 
    import android.app.Activity; 
    import android.content.Intent; 
    import android.database.Cursor; 
    import android.os.Bundle; 
    import android.view.Menu; 
    import android.view.MenuItem; 
    import android.view.View; 
    import android.view.View.OnClickListener; 
    import android.widget.ArrayAdapter; 
    import android.widget.Button; 
    import android.widget.Spinner; 

    public class Monthly extends Activity{ 

     DatabaseAdapter dbAdapter; 
     private Spinner emonth; 
     private Spinner eyear; 
     private Button submit; 
     private double price1, price2, price3, price4, price5, price6, price7; 

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

      emonth = (Spinner)findViewById(R.id.spinner1); 
      ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, 
        R.array.month, android.R.layout.simple_spinner_item); 
      adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 
      emonth.setAdapter(adapter); 

      eyear = (Spinner)findViewById(R.id.spinner2); 
      ArrayAdapter<CharSequence> adapter2 = ArrayAdapter.createFromResource(this, 
        R.array.years, android.R.layout.simple_spinner_item); 
      adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 
      eyear.setAdapter(adapter2); 

      submit = (Button) findViewById(R.id.button1); 
      submit.setOnClickListener(submitOnClickListener); 

     } 

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

     @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. 
      int id = item.getItemId(); 
      if (id == R.id.action_settings) { 
       return true; 
      } 
      return super.onOptionsItemSelected(item); 
     } 


     OnClickListener submitOnClickListener = 
       new OnClickListener(){ 
     @Override 
     public void onClick(View v) { 
      // TODO Auto-generated method stub 

      if(v.getId()==R.id.button1) 
       { 

       String month=emonth.getSelectedItem().toString(); 
       String year=eyear.getSelectedItem().toString(); 

       dbAdapter.open(); 
       Cursor price1=dbAdapter.queryFoodMonth(month, year); 

       Cursor price2=dbAdapter.queryClothingMonth(month, year); 

       Cursor price3=dbAdapter.queryElectronicsMonth(month, year); 

       Cursor price4=dbAdapter.queryUtilityMonth(month, year); 

       Cursor price5=dbAdapter.queryEntertainmentMonth(month, year); 

       Cursor price6=dbAdapter.queryFuelMonth(month, year); 

       Cursor price7=dbAdapter.queryOtherMonth(month, year); 
       dbAdapter.close(); 

         Intent intent = new Intent(Monthly.this,WebChart.class); 

          intent.putExtra("PRICE1", getNum(price1)); 
          intent.putExtra("PRICE2", getNum(price2)); 
          intent.putExtra("PRICE3", getNum(price3)); 
          intent.putExtra("PRICE4", getNum(price4)); 
          intent.putExtra("PRICE5", getNum(price5)); 
          intent.putExtra("PRICE6", getNum(price6)); 
          intent.putExtra("PRICE7", getNum(price7)); 
          startActivity(intent); 

        } 
     }  
         }; 

         private double getNum(Cursor price){ 

          double num = 0.0; 
          String stringNum = price.toString(); 
          if(!stringNum.equals("")){ 
           num = Integer.valueOf(stringNum); 
          } 

          return (num); 
         } 

     } 

这是数据库适配器中给出游标的代码。

public Cursor queryFoodMonth(String month,String year) 
{ 
    Cursor c1 = database.rawQuery("SELECT SUM(price) FROM items where month= \" "+month+" \" AND year= \" "+year+" \" AND category = \"Food\";",null); 

     if (c1 !=null) { 
      c1.moveToFirst(); 
     } 

     return c1; 

} 

public Cursor queryClothingMonth(String month,String year) 
{ 
    Cursor c2 = database.rawQuery("SELECT SUM(price) FROM items where month= \" "+month+" \" AND year= \" "+year+" \" AND category = \"Clothing\";",null); 

     if (c2 !=null) { 
      c2.moveToFirst(); 
     } 
     return c2; 
} 

public Cursor queryElectronicsMonth(String month,String year) 
{ 
    Cursor c3 = database.rawQuery("SELECT SUM(price) FROM items where month= \" "+month+" \" AND year= \" "+year+" \" AND category = \"Electronics\";",null); 

     if (c3 !=null) { 
      c3.moveToFirst(); 
     } 
     return c3; 
} 

public Cursor queryUtilityMonth(String month,String year) 
{ 
    Cursor c4 = database.rawQuery("SELECT SUM(price) FROM items where month= \" "+month+" \" AND year= \" "+year+" \" AND category = \"Utility\";",null); 

     if (c4 !=null) { 
      c4.moveToFirst(); 
     } 
     return c4; 
} 

public Cursor queryEntertainmentMonth(String month,String year) 
{ 
    Cursor c5 = database.rawQuery("SELECT SUM(price) FROM items where month= \" "+month+" \" AND year= \" "+year+" \" AND category = \"Entertainment\";",null); 

     if (c5 !=null) { 
      c5.moveToFirst(); 
     } 
     return c5; 
} 

public Cursor queryFuelMonth(String month,String year) 
{ 
    Cursor c6 = database.rawQuery("SELECT SUM(price) FROM items where month= \" "+month+" \" AND year= \" "+year+" \" AND category = \"Fuel\";",null); 

     if (c6 !=null) { 
      c6.moveToFirst(); 
     } 
     return c6; 
} 

public Cursor queryOtherMonth(String month,String year) 
{ 
    Cursor c7 = database.rawQuery("SELECT SUM(price) FROM items where month= \" "+month+" \" AND year= \" "+year+" \" AND category = \"Other\";",null); 

     if (c7 !=null) { 
      c7.moveToFirst(); 
     } 
     return c7; 
} 

而且这个logcat的错误报告：

12-03 17:31:25.632: E/AndroidRuntime(1993): FATAL EXCEPTION: main 
12-03 17:31:25.632: E/AndroidRuntime(1993): Process: com.csj.monthlybudg, PID: 1993 
12-03 17:31:25.632: E/AndroidRuntime(1993): java.lang.NullPointerException 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at com.csj.monthlybudg.Monthly$1.onClick(Monthly.java:78) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at android.view.View.performClick(View.java:4438) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at android.view.View$PerformClick.run(View.java:18422) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at android.os.Handler.handleCallback(Handler.java:733) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at android.os.Handler.dispatchMessage(Handler.java:95) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at android.os.Looper.loop(Looper.java:136) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at android.app.ActivityThread.main(ActivityThread.java:5001) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at java.lang.reflect.Method.invokeNative(Native Method) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at java.lang.reflect.Method.invoke(Method.java:515) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 
12-03 17:31:25.632: E/AndroidRuntime(1993):  at dalvik.system.NativeStart.main(Native Method) 

我可以看到，错误是行78而打开数据库连接，但我不明白什么是错的。任何帮助将不胜感激，如果你发现我的问题天真，请不要苛刻我是新来的android和java。 谢谢！

Answer 1

您需要调用dbAdapter.open();

空指针异常之前做这样的事情dbAdapter = new DatabaseAdapter()当您尝试使用（在这种情况下dbAdapter）指向没有在存储器中的参考，通常会出现，即你有没有但创造任何指向的参考。