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我从教程中找到了这个源代码，但是当我运行它时它崩溃了。

我的日志猫：

01-25 00:26:30.898: E/AndroidRuntime(2762): FATAL EXCEPTION: main
01-25 00:26:30.898: E/AndroidRuntime(2762): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.pinchtapzoom/com.pinchtapzoom.AssignmentTracker}: java.lang.NullPointerException
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.app.ActivityThread.access$600(ActivityThread.java:127)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.os.Looper.loop(Looper.java:137)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.app.ActivityThread.main(ActivityThread.java:4441)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at java.lang.reflect.Method.invokeNative(Native Method)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at java.lang.reflect.Method.invoke(Method.java:511)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at dalvik.system.NativeStart.main(Native Method)
01-25 00:26:30.898: E/AndroidRuntime(2762): Caused by: java.lang.NullPointerException
01-25 00:26:30.898: E/AndroidRuntime(2762):     at com.pinchtapzoom.AssignmentTracker.onCreate(AssignmentTracker.java:70)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.app.Activity.performCreate(Activity.java:4465)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-25 00:26:30.898: E/AndroidRuntime(2762):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
01-25 00:26:30.898: E/AndroidRuntime(2762):     ... 11 more

这是代码开始崩溃的地方：

//---retrieves all the records---

public Cursor getAllRecords() 
{
    db = DBHelper.getWritableDatabase();
     Cursor mCursor = db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_TITLE,
            KEY_DUEDATE, KEY_COURSE, KEY_NOTES}, null, null, null, null, null);
    if (mCursor != null) {
        mCursor.moveToFirst();
    }
    return mCursor;
}

和

//---get all Records---

    db.open();
    Cursor c = db.getAllRecords();
    startManagingCursor(c);
    if (c.moveToFirst())
    {
        do {          
            DisplayRecord(c);
        } while (c.moveToNext());
    }
    db.close();

这是 AssignmentTracker.java 的代码：

<code> 

package com.pinchtapzoom;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.Toast;

public class AssignmentTracker extends Activity {

        /** Called when the activity is first created. */
 @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);


            setContentView(R.layout.main);

            Button addBtn = (Button)findViewById(R.id.add);
            addBtn.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    Intent i = new Intent(AssignmentTracker.this, addassignment.class);
                    startActivity(i);
                }
            });


            try {           
                String destPath = "/data/data/" + getPackageName() + "/databases/AssignmentDB.db";
                File f = new File(destPath);            
                if (!f.exists()) {          
                    CopyDB( getBaseContext().getAssets().open("mydb"), 
                        new FileOutputStream(destPath));
                }
            } catch (FileNotFoundException e) {         
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            DBAdapter db = new DBAdapter(this); 
            //---add an assignment---

            db.open();        
            long id = db.insertRecord("Hello World", "2/18/2012", "DPR 224", "First Android Project");        
            id = db.insertRecord("Workbook Exercises", "3/1/2012", "MAT 100", "Do odd numbers");
            db.close();


            //---get all Records---

            db.open();
            Cursor c = db.getAllRecords();
            startManagingCursor(c);
            if (c.moveToFirst())
            {
                do {          
                    DisplayRecord(c);
                } while (c.moveToNext());
            }
            db.close();
            /*

            //---get a Record---
            db.open();
            Cursor c = db.getRecord(2);
            if (c.moveToFirst())        
                DisplayRecord(c);
            else
                Toast.makeText(this, "No Assignments found", Toast.LENGTH_LONG).show();
            db.close();
            */


            //---update Record---
            /*
            db.open();
            if (db.updateRecord(1, "Hello Android", "2/19/2012", "DPR 224", "First Android Project"))
                Toast.makeText(this, "Update successful.", Toast.LENGTH_LONG).show();
            else
                Toast.makeText(this, "Update failed.", Toast.LENGTH_LONG).show();        
            db.close();
            */

            /*
            //---delete a Record---
            db.open();
            if (db.deleteRecord(1))
                Toast.makeText(this, "Delete successful.", Toast.LENGTH_LONG).show();
            else
                Toast.makeText(this, "Delete failed.", Toast.LENGTH_LONG).show();            
            db.close();
            */
        }

        private class DBAdapter extends BaseAdapter {
            private LayoutInflater mInflater;
            public DBAdapter(AssignmentTracker assignmentTracker) {
                // TODO Auto-generated constructor stub
            }

            public Cursor getAllRecords() {
                // TODO Auto-generated method stub
                return null;
            }

            public Cursor getAllRecords(int i, int j) {
                // TODO Auto-generated method stub
                return null;
            }

            //private ArrayList<>

            public void close() {
                // TODO Auto-generated method stub

            }

            public long insertRecord(String string, String string2, String string3,
                    String string4) {
                // TODO Auto-generated method stub
                return 0;
            }

            public void open() {
                // TODO Auto-generated method stub

            }

            @Override
            public int getCount() {

                return 0;
            }

            @Override
            public Object getItem(int arg0) {

                return null;
            }

            @Override
            public long getItemId(int arg0) {

                return 0;
            }

            @Override
            public View getView(int arg0, View arg1, ViewGroup arg2) {

                return null;
            }

        }

        public void CopyDB(InputStream inputStream, OutputStream outputStream) 
        throws IOException {
            //---copy 1K bytes at a time---
            byte[] buffer = new byte[1024];
            int length;
            while ((length = inputStream.read(buffer)) > 0) {
                outputStream.write(buffer, 0, length);
            }
            inputStream.close();
            outputStream.close();
        }

        public void DisplayRecord(Cursor c)
        {
            Toast.makeText(this, 
                    "id: " + c.getString(0) + "\n" +
                    "Title: " + c.getString(1) + "\n" +
                    "Due Date:  " + c.getString(2),
                    Toast.LENGTH_SHORT).show();        
        } 

        public void addAssignment(View view)
        {

            Intent i = new Intent("com.pinchtapzoom.addassignment");
            startActivity(i);
            Log.d("TAG", "Clicked");
        }

    }

这是 DBAdapter.java 的代码：

package com.pinchtapzoom;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBAdapter {
    public static final String KEY_ROWID = "id";
    public static final String KEY_TITLE = "title";
    public static final String KEY_DUEDATE = "duedate";
    public static final String KEY_COURSE = "course";
    public static final String KEY_NOTES = "notes";
    private static final String TAG = "DBAdapter";

    private static final String DATABASE_NAME = "AssignmentsDB.db";
    private static final String DATABASE_TABLE = "assignments";
    private static final int DATABASE_VERSION = 2;

    private static final String DATABASE_CREATE =
        "create table if not exists assignments (id integer primary key autoincrement, "
        + "title VARCHAR not null, duedate date, course VARCHAR, notes VARCHAR );";

    private final Context context;    

    private DatabaseHelper DBHelper;
    private SQLiteDatabase db;

    public DBAdapter(Context ctx) 
    {


        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper 
    {
        DatabaseHelper(Context context) 
        {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);

        }

        @Override
        public void onCreate(SQLiteDatabase db) 
        {
            try {
                db.execSQL(DATABASE_CREATE);    
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
        {
            Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                    + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS contacts");
            onCreate(db);
        }
    }    

    //---opens the database---
    public DBAdapter open() throws SQLException 
    {
        db = DBHelper.getWritableDatabase();
        return this;
    }

    //---closes the database---    
    public void close() 
    {
        DBHelper.close();
    }

    //---insert a record into the database---
    public long insertRecord(String title, String duedate, String course, String notes) 
    {
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_TITLE, title);
        initialValues.put(KEY_DUEDATE, duedate);
        initialValues.put(KEY_COURSE, course);
        initialValues.put(KEY_NOTES, notes);
        return db.insert(DATABASE_TABLE, null, initialValues);
    }

    //---deletes a particular record---
    public boolean deleteContact(long rowId) 
    {
        return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
    }

    //---retrieves all the records---
    public Cursor getAllRecords() 
    {
        db = DBHelper.getWritableDatabase();
         Cursor mCursor = db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_TITLE,
                KEY_DUEDATE, KEY_COURSE, KEY_NOTES}, null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    //---retrieves a particular record---
    public Cursor getRecord(long rowId) throws SQLException 
    {
        Cursor mCursor =
                db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
                KEY_TITLE, KEY_DUEDATE, KEY_COURSE, KEY_NOTES}, 
                KEY_ROWID + "=" + rowId, null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    //---updates a record---
    public boolean updateRecord(long rowId, String title, String duedate, String course, String notes) 
    {
        ContentValues args = new ContentValues();
        args.put(KEY_TITLE, title);
        args.put(KEY_DUEDATE, duedate);
        args.put(KEY_COURSE, course);
        args.put(KEY_NOTES, notes);
        return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
    }
}

教程是：这里

当我取消注释代码时它停止工作。关于这个问题有很多问题，但没有明确的解决方案。我刚开始学习 SQLite，所以需要一些帮助来找到解决方案。

提前致谢

4

2 回答 2

1

The problem is that you have two classes named DBAdapter and you are using the wrong one...
Simply remove the entire DBAdapter class that starts with:

private class DBAdapter extends BaseAdapter {

This DBAdapter inside AssignmentTracker does nothing anyway.

于 2013-01-25T00:02:36.147 回答
0

logcat 会告诉你究竟是哪一行导致了异常，但它可能是

Cursor mCursor = db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_TITLE,
        KEY_DUEDATE, KEY_COURSE, KEY_NOTES}, null, null, null, null, null);

因为您没有检查getWritableDatabase()返回的数据库并且不为空，或者

if (c.moveToFirst())

因为您没有检查db.getAllRecords();返回的游标而不是空值。

于 2013-01-24T23:52:50.517 回答