SQLite + setAdapter = NPE_问答_开发者_运维开发者技术经验分享

There is a NPE at the last line, I can't figure out where it's coming from. Any ideas?

  mySQLiteAdapter = new SQLiteAdapter(this);
  mySQLiteAdapter.openToRead();
  listContent = (ListView)findViewById(R.id.contentlist);
  Cursor cursor = mySQLiteAdapter.queueAll();
  startManagingCursor(cursor);

  String[] from = new String[]{SQLiteAdapter.KEY_CHOICE,         
  SQLiteAdapter.KEY_AMOUNT};
  int[] to = new int[]{R.id.txtChoice, R.id.txtAmtSpent};

  SimpleCursorAdapter cursorAdapter =
   new SimpleCursorAdapter(this, R.layout.row2, cursor, from, to);
  mySQLiteAdapter.close();
  listContent.setAdapter(cursorAdapter);

HERE IS THE ERROR

    06-19 01:27:50.832: ERROR/AndroidRuntime(1425): FATAL EXCEPTION: main
06-19 01:27:50.832: ERROR/AndroidRuntime(1425): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.whycom.idontknow/com.whycom.idontknow.ListSpent}: java.lang.NullPointerException
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at android.os.Looper.loop(Looper.java:123)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at android.app.ActivityThread.main(ActivityThread.java:4627)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at java.lang.reflect.Method.invokeNative(Native Method)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at java.lang.reflect.Method.invoke(Method.java:521)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at dalvik.system.NativeStart.main(Native Method)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425): Caused by: java.lang.NullPointerException
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at com.whycom.idontknow.ListSpent.makeList(ListSpent.java:161)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at com.whycom.idontknow.ListSpent.onCreate(ListSpent.java:79)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
06-19 01:27:50.832: ERROR/AndroidRuntime(1425):     ... 11 more

The whole code is below:

 package com.whycom.idontknow;
import java.util.Collections; 
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import java.io.BufferedReader;
import java.io.EOFException;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Array;
import java.util.ArrayList;

import android.app.ListActivity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.database.Cursor;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.SimpleCursorAdapter;
import android.widget.TextView;
import android.widget.Toast;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class ListSpent extends ListActivity {
    private SQLiteAdapter mySQLiteAdapter;
    //Intent splat;
    //Bundle b;

    //  String[] amounts;
    //  String[] expenditureArray;
    String choice; 
    String amount; 
    int count;
    String[] dataAry= new String[100];
    //String[] choices;
    String Count;
    SharedPreferences prefs; 
    TextView txtAmtSpent;
    TextView txtChoice;
    ListAdapter adapter;
    ListView listContent;
    int j;
//  ListView listContent;


    //      PreferenceManager.getDefaultSharedPreferences(this);


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.mainlist);

        prefs = PreferenceManager.getDefaultSharedPreferences(this);
        //ListView listContent = (ListView)findViewById(R.id.contentlist);
        initVars();
        try {
            buildArray();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }


        makeList();
    }
    static class ViewHolder{
        TextView text;
        TextView button;
    }



    public void buildArray() throws IOException{
        //ArrayList<String> al = new ArrayList<String>(); 

        InputStream instream;
        try {
            instream = openFileInput("mySpends.txt");
            InputStreamReader inputreader = new InputStreamReader(instream);
            BufferedReader buffreader = new BufferedReader(inputreader);

            Count = prefs.getString("Count" , "0");
            count = Integer.parseInt(Count);





            for (int i = 0; i < ((count)*2); i=i+2){
                choice = buffreader.readLine();
                amount = buffreader.readLine();
                dataAry[i] = choice;
                dataAry[i+1] = amount;
                //trial

            }


        } catch (FileNotFoundException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();

        }
    }

    private void initVars(){

        txtAmtSpent = (TextView)findViewById(R.id.txtAmtSpent);
        txtChoice = (TextView)findViewById(R.id.txtChoice);
        listContent = (ListView)findViewById(R.id.contentlist);

    }


    private void makeList(){
         mySQLiteAdapter = new SQLiteAdapter(this);
 开发者_运维知识库         mySQLiteAdapter.openToWrite();
          mySQLiteAdapter.deleteAll();
        ListView listContent = (ListView)findViewById(R.id.contentlist);
        String [] dataAryArray = new String[(count)*2];
        j = 0;
        int ind = (count)*2-1;
        for (int i = -1; i < ind; ind = ind - 2){
            dataAryArray[j] = dataAry[ind];
            dataAryArray[j+1] = dataAry[ind-1];

              mySQLiteAdapter.insert(dataAryArray[j],dataAryArray[j+1]);

            j=j+2;


        }
         mySQLiteAdapter.close();

          mySQLiteAdapter.openToRead();
          Cursor cursor = mySQLiteAdapter.queueAll();
          startManagingCursor(cursor);
          String c=SQLiteAdapter.KEY_CHOICE;
          String a=SQLiteAdapter.KEY_AMOUNT;
          String[] from = new String[]{SQLiteAdapter.KEY_CHOICE, SQLiteAdapter.KEY_AMOUNT};
          int[] to = new int[]{R.id.txtChoice, R.id.txtAmtSpent};

          SimpleCursorAdapter cursorAdapter =
           new SimpleCursorAdapter(this, R.id.text, cursor, from, to);

          listContent.setAdapter(cursorAdapter);
          mySQLiteAdapter.close();






        //      adapter = new ArrayAdapter<String>(this, 
        //              android.R.layout.simple_list_item_1, dataAryArray);
        //      setListAdapter(adapter);            
        ListView lv = getListView();
        lv.setTextFilterEnabled(true);
        lv.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                //       When clicked, show a toast with the TextView text
                //              Toast.makeText(getApplicationContext(), ((TextView) view).getText(),
                //                      Toast.LENGTH_SHORT).show();
                Toast.makeText(getApplicationContext(), "Toast",
                        Toast.LENGTH_SHORT).show();
            }
        }
        )
        ;
    }

}

Here is the XML named mainlist.xml:

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
       android:orientation="vertical"
       android:layout_width="fill_parent"
       android:layout_height="fill_parent"
       >
     <TextView
       android:layout_width="fill_parent"
       android:layout_height="wrap_content"
       android:text="@string/hello"
       />
     <ListView
     android:id="@android:id/list"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"/>
     </LinearLayout>

listContent is not found. You may need to call setContentView before trying findViewById.

Update

Based on more information and provided code, since your declared ListView id

android:id="@android:id/list"

it refers to Android id not your own. So you need to search for it via

findViewById(android.R.id.list)

not your package R.

But why would you even need it if ListActivity provides all methods so you don't have to access it directly? For example,

setListAdapter(...);

See example here http://www.higherpass.com/Android/Tutorials/Creating-Lists-Using-The-Android-Listactivity/

It would be really helpful to include the stack trace for the NPE. But I suspect the problem might be this line, immediately before the NPE:

  mySQLiteAdapter.close();

If the SQLiteAdapter class is similar to the NotesDbAdapter class from the Android Notepad tutorial, then you shouldn't be closing it there; that will invalidate your cursor. Instead, close it in your activity's onDestroy method. (That last link goes to a blog post that I wrote regarding when and how to close these objects.)