我正在编写一个 android 应用程序，它允许用户在数据库中搜索并根据他们的搜索查看数据库中的结果。目前我收到一个 NullPointerException 并且我不确定如何解决这个问题，因为我已经尝试了很多方法来确保光标不为空，这些抛出错误的行前面有 (*)。下面列出了我的代码以及 logcat。. 我正在使用 eclipse sdk 4.2 并在我的摩托罗拉 Droid Bionic 和模拟器上进行测试。我是 android 编程新手，我学到的一切都来自教程或其他在线资源。任何帮助是极大的赞赏
创建数据库的主要活动：
package com.example.database;
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;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity
{
EditText dEdit;
public static final String KEY_ROWID = "_id";
public static final String KEY_BUSINESS = "business";
public static final String KEY_ADDRESS = "address";
public static final String KEY_PHONE = "phone";
public static final String KEY_HOURS = "hours";
public static final String KEY_WEB = "website";
public static final String KEY_TYPE = "type";
private static final String TAG = "MainActivity";
private static final String DATABASE_NAME = "LocalDB";
private static final String DATABASE_TABLE = "Business";
private static final int DATABASE_VERSION = 2;
private static final String DATABASE_CREATE =
"create table Business (_id integer primary key autoincrement, "
+ "business text not null, address text not null, phone text not null,hours text not null,website text not null,type text not null"
+ ")";
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase mDB;
public MainActivity(Context ctx)
{
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
try{
mDB=db;
mDB.execSQL(DATABASE_CREATE);
} catch(SQLException e){
e.printStackTrace();
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion)
{
try{
mDB=db;
Log.w(TAG, "Upgrading database from version " + oldVersion
+ " to "
+ newVersion + ", which will destroy all old data");
mDB.execSQL("DROP TABLE IF EXISTS Business");
onCreate(mDB);
}catch (SQLException e){
e.printStackTrace();
}
}
}
//---opens the database---
public MainActivity open() throws SQLException
{
mDB = DBHelper.getWritableDatabase();
return this;
}
//---closes the database---
public void close()
{
DBHelper.close();
}
//---insert a title into the database---
public long insertTitle(String business, String address, String phone, String hours, String website, String type)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_BUSINESS, business);
initialValues.put(KEY_ADDRESS, address);
initialValues.put(KEY_PHONE, phone);
initialValues.put(KEY_HOURS, hours);
initialValues.put(KEY_WEB, hours);
initialValues.put(KEY_TYPE, type);
return mDB.insert(DATABASE_TABLE, null, initialValues);
}
//---deletes a particular title---
public boolean deleteTitle(long rowId)
{
return mDB.delete(DATABASE_TABLE, KEY_ROWID +
"=" + rowId, null) > 0;
}
//---retrieves all the titles---
public Cursor getAllTitles()
{
return mDB.query(DATABASE_TABLE, new String[] {
KEY_ROWID,
KEY_BUSINESS,
KEY_ADDRESS,
KEY_PHONE,
KEY_HOURS,
KEY_WEB,
KEY_TYPE},
null,
null,
null,
null,
null);
}
//---retrieves a particular title---
public Cursor getTitle(long rowId) throws SQLException
{
Cursor mCursor =
mDB.query(true, DATABASE_TABLE, new String[] {
KEY_ROWID,
KEY_BUSINESS,
KEY_ADDRESS,
KEY_PHONE,
KEY_HOURS,
KEY_WEB,
KEY_TYPE
},
KEY_ROWID + "=" + rowId,
null,
null,
null,
null,
null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
//---updates a title---
public boolean updateTitle(long rowId, String business,
String address, String phone, String hours, String website, String type)
{
ContentValues args = new ContentValues();
args.put(KEY_BUSINESS, business);
args.put(KEY_ADDRESS, address);
args.put(KEY_PHONE, phone);
args.put(KEY_HOURS,hours);
args.put(KEY_WEB,website);
args.put(KEY_TYPE, type);
return mDB.update(DATABASE_TABLE, args,
KEY_ROWID + "=" + rowId, null) > 0;
}
}
public Cursor getBusinessInfo(String name) {
// TODO Auto-generated method stub
return mDB.rawQuery("SELECT business,address,phone,hours,website,type FROM Business where name like ?", new String[]{"%"+name+"%"});
}
public Cursor getBusinessType(String type) {
// TODO Auto-generated method stub
return mDB.rawQuery("SELECT business,address,phone,hours,website,type FROM Business where type like ?", new String[]{"%"+type+"%"});
}
}
搜索在数据库中发生的位置：
package com.example.database;
import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class DBUse extends Activity {
EditText dEdit;
SQLiteDatabase data;
public static final String KEY_ROWID = "_id";
public static final String KEY_BUSINESS = "business";
public static final String KEY_ADDRESS = "address";
public static final String KEY_PHONE = "phone";
public static final String KEY_HOURS = "hours";
public static final String KEY_WEB = "website";
public static final String KEY_TYPE = "type";
@Override
public void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MainActivity datab = new MainActivity(this);
Button buttonName =(Button)findViewById(R.id.buttonName);
buttonName.setOnClickListener(startName);
Button buttonType =(Button)findViewById(R.id.buttonType);
buttonType.setOnClickListener(startType);
dEdit =(EditText)findViewById(R.id.textView1);
datab.open();
Cursor c = datab.getAllTitles();
if((c!=null) &&c.moveToFirst())
{
do{DisplayTitle(c);
}while (c.moveToNext());
}
datab.open();
Cursor b = datab.getAllTitles();
if ((b!=null) && b.moveToFirst())
DisplayTitle(b);
else
Toast.makeText(this,"No business found",Toast.LENGTH_LONG).show();
}
//displays the data
public void DisplayTitle(Cursor c) {
Toast.makeText(this,
"Name: " + c.getString(1)+"\n"+
"Address:" + c.getString(2)+"\n"+
"Phone:" + c.getString(3)+"\n"+
"Hours:" + c.getString(4)+"\n"+
"Website"+ c.getShort(5)+
"Type" + c.getShort(6),
Toast.LENGTH_LONG).show();
}
//Informs the user what is being searched
private OnClickListener startName=new OnClickListener(){
public void onClick (View v) {
Cursor cur = data.getBusinessInfo(dEdit.getText().toString());
String result="";
int iRow=cur.getColumnIndex(KEY_ROWID);
int iName=cur.getColumnIndex(KEY_BUSINESS);
int iAddress=cur.getColumnIndex(KEY_ADDRESS);
int iPhone=cur.getColumnIndex(KEY_PHONE);
int iHours=cur.getColumnIndex(KEY_HOURS);
int iWebsite=cur.getColumnIndex(KEY_WEB);
int iType=cur.getColumnIndex(KEY_TYPE);
Toast.makeText(DBUse.this, "Searching by Name", Toast.LENGTH_LONG).show();
// log.d("result",DBUse.getString(0));
for(cur.moveToFirst(); !cur.isAfterLast(); cur.moveToNext()){
result=result +cur.getString(iRow) + " "
+cur.getString(iName) + " "
+cur.getString(iAddress) + " "
+cur.getString(iPhone) + " "
+cur.getString(iHours) + " "
+cur.getString(iWebsite) + " "
+cur.getString(iType) + " " + "\n";
Toast.makeText(DBUse.this, result, Toast.LENGTH_LONG).show();
};
return;
}
};
//Informs the user what is being searched
private OnClickListener startType=new OnClickListener(){
public void onClick (View v){
Cursor cur=data.getBusinessType(dEdit.getText().toString());
String result="";
int iRow=cur.getColumnIndex(KEY_ROWID);
int iName=cur.getColumnIndex(KEY_BUSINESS);
int iAddress=cur.getColumnIndex(KEY_ADDRESS);
int iPhone=cur.getColumnIndex(KEY_PHONE);
int iHours=cur.getColumnIndex(KEY_HOURS);
int iWebsite=cur.getColumnIndex(KEY_WEB);
int iType=cur.getColumnIndex(KEY_TYPE);
Toast.makeText(DBUse.this, "Searching by Name", Toast.LENGTH_LONG).show();
// log.d("result",DBUse.getString(0));
for(cur.moveToFirst(); !cur.isAfterLast(); cur.moveToNext()){
result=result +cur.getString(iRow) + " "
+cur.getString(iName) + " "
+cur.getString(iAddress) + " "
+cur.getString(iPhone) + " "
+cur.getString(iHours) + " "
+cur.getString(iWebsite) + " "
+cur.getString(iType) + " " + "\n";
Toast.makeText(DBUse.this, result, Toast.LENGTH_LONG).show();
};
return;
};
};
}
数据来自哪里：包 com.example.database；导入android.app.Activity；导入android.os.Bundle；public class DBActivity extends Activity { //MainActivity eventsData; //编辑文本输出；@Override public void onCreate(Bundle savedInstanceState) { // TODO 自动生成的方法存根 super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); MainActivity db= new MainActivity(this);
//output = (EditText) findViewById(R.id.textView1);
//type.setOnClickListener(
// new OnClickListener(){
// public void onClick(View view){
// Log.v("Entry",dEdit.getText().toString());
// }
/// });
//try{String destPath="/data/data" +getPackageName()+ "/databases/BloomBusiness";
// File f = new File(destPath);
// if(!f.exists()){
// CopyDB(getBaseContext().getAssets().open("db"), new FileOutputStream(destPath));
// }
//
//
//}catch(FileNotFoundException e){
// e.printStackTrace();
//}catch(IOException e){
// e.printStackTrace();
//}
db.open();
//inserting all data
long id;
id =db.insertTitle("BloomingFoods","419 E. Kirkwood Ave. Bloomington, IN", "812-336-5300", "M-Sat:8AM-9PM Sun:9AM-8PM","http://www.bloomingfoods.coop","Grocery");
id=db.insertTitle("BloomingFoods","316 W. 6th Street Bloomington, IN", "812-333-5300", "M-Sat:7AM-10PM Sun:9AM-9PM","http://www.bloomingfoods.coop","Grocery");
id=db.insertTitle("BloomingFoods","3220 E. 3rd Street Bloomington, IN", "812-336-5300", "M-Sun:8AM-10PM","http://www.bloomingfoods.coop","Grocery");
id=db.insertTitle("The Uptown Cafe","102 E. Kirkwood Ave. Bloomington, IN", "812-339-0900", "M-Sat:8AM-9PM Sun:9AM-8PM", "http://www.the-uptown.com/","Cajun-Creole");
id=db.insertTitle("Crazy Horse","214 W. Kirkwood Ave. Bloomington, IN", "812-336-8877", "M-Sat:11AM-2AM Sun:Noon-Midnight", "http://www.crazyhorseindiana.com/","Restaurant & Live Music");
id=db.insertTitle("FARMbloomington","108 E. Kirkwood Ave. Bloomington, IN", "812-323-0002", "Tue.-Thurs.:8AM-10PM F:8AM-1AM Sat: 10AM-3AM Sun: 10AM-10PM","http://www.farm-bloomington.com","Grocery");
id=db.insertTitle("Laughing Planet","322 E. Kirkwood Ave. Bloomington, IN", "812-323-2233", "M-Sun:11AM-9PM","http://www.facebook.com/laughingplanetbtown","Burritos & Salads");
id=db.insertTitle("Soma Coffeehouse","322 E. Kirkwood Bloomington, IN", "812-331-2770", "M-Sat:7AM-11PM Sun:8AM-11PM","http://www.iheartsoma.com","Coffee House");
id=db.insertTitle("Upland Brewing Company","350 W. 11th St. Bloomington, IN", "812-336-2337", "M-Thurs:11AM-Midnight F-Sat:11AM-1AM Sun: Noon-Midnight","http://www.uplandbeer.com","Brewery & Restaraunt");
id=db.insertTitle("Nick's English Hut","423 E. Kirkwood Bloomington, IN", "812-332-4040", "M-Sat:11AM-2AM Sun: Noon-Midnight","http://www.nicksenglishhut.com","Bar & Restaraunt");
id=db.insertTitle("The Village Deli","409 E. Kirkwood Ave. Bloomington, IN", "812-336-2303", "M-F:7AM-8PM Sat-Sun 8AM-8PM","http://www.villagedeli.biz","Breakfast,Lunch,Dinner");
id=db.insertTitle("Rachael's Cafe","300 E. 3rd St. Bloomington, IN", "812-330-1882", "M-F:8AM-9PM Sat-Sun 9AM-9PM","http://www.rachaelscafe.com","Coffee House & Live Music");
id=db.insertTitle("Happy Pig","1604 W. 7th St. Bloomington, IN", "None", "W:Sample Gates Noon-3PM Thurs:Sample Gates Noon-3PM F:Atlas Bar 11:30PM-3:30AM Sat:Courthouse Square 11:30PM-3:30AM","http://www.happypigbloomington.com","BBQ Streetfood");
id=db.insertTitle("Lennie's Restaurant and Brewpub","1795 E. 10th St. Bloomington, IN", "812-323-2112", "Sun-Th:11AM-11PM F-Sat 11AM-Midnight","http://www.lenniesgourmetpizza.com","Bar & Restaurant");
id=db.insertTitle("Pizza X","1791 E. 10th St. Bloomington, IN", "812-339-7737", "Sun-Tues:11AM-2AM Wed-Thur: 11AM-3AM F-Sat:11AM-4AM","http://www.pizzaxbloomington.com","Pizza");
id=db.insertTitle("Pizza X","1610 W. 3rd St. Bloomington, IN", "812-332-2522", "Sun-Wed:4PM-Midnight Thur: 4PM-3AM F-Sat:4PM-4AM","http://www.pizzaxbloomington.com","Pizza");
id=db.insertTitle("Pizza X","877 S. College Mall Rd. Bloomington, IN", "812-355-5000", "Sun-Wed:4PM-Midnight Thur: 4PM-3AM F-Sat:4PM-4AM","http://www.pizzaxbloomington.com","Pizza");
}
日志猫：
04-28 18:06:32.648: E/Trace(692): error opening trace file: No such file or directory (2)
04-28 18:06:33.160: D/dalvikvm(692): GC_FOR_ALLOC freed 40K, 2% free 10842K/11011K, paused 44ms, total 46ms
04-28 18:06:33.160: I/dalvikvm-heap(692): Grow heap (frag case) to 11.204MB for 614416-byte allocation
04-28 18:06:33.298: D/dalvikvm(692): GC_CONCURRENT freed 1K, 2% free 11441K/11655K, paused 88ms+4ms, total 135ms
04-28 18:06:33.368: D/dalvikvm(692): GC_FOR_ALLOC freed 0K, 2% free 11441K/11655K, paused 28ms, total 28ms
04-28 18:06:33.381: I/dalvikvm-heap(692): Grow heap (frag case) to 12.245MB for 1093136-byte allocation
04-28 18:06:33.498: D/dalvikvm(692): GC_CONCURRENT freed 0K, 2% free 12508K/12743K, paused 76ms+7ms, total 126ms
04-28 18:06:34.188: D/gralloc_goldfish(692): Emulator without GPU emulation detected.
04-28 18:07:12.528: D/AndroidRuntime(692): Shutting down VM
04-28 18:07:12.528: W/dalvikvm(692): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
04-28 18:07:12.542: E/AndroidRuntime(692): FATAL EXCEPTION: main
04-28 18:07:12.542: E/AndroidRuntime(692): java.lang.NullPointerException
04-28 18:07:12.542: E/AndroidRuntime(692): at com.example.database.DBUse$2.onClick(DBUse.java:123)
04-28 18:07:12.542: E/AndroidRuntime(692): at android.view.View.performClick(View.java:4084)
04-28 18:07:12.542: E/AndroidRuntime(692): at android.view.View$PerformClick.run(View.java:16966)
04-28 18:07:12.542: E/AndroidRuntime(692): at android.os.Handler.handleCallback(Handler.java:615)
04-28 18:07:12.542: E/AndroidRuntime(692): at android.os.Handler.dispatchMessage(Handler.java:92)
04-28 18:07:12.542: E/AndroidRuntime(692): at android.os.Looper.loop(Looper.java:137)
04-28 18:07:12.542: E/AndroidRuntime(692): at android.app.ActivityThread.main(ActivityThread.java:4745)
04-28 18:07:12.542: E/AndroidRuntime(692): at java.lang.reflect.Method.invokeNative(Native Method)
04-28 18:07:12.542: E/AndroidRuntime(692): at java.lang.reflect.Method.invoke(Method.java:511)
04-28 18:07:12.542: E/AndroidRuntime(692): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-28 18:07:12.542: E/AndroidRuntime(692): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-28 18:07:12.542: E/AndroidRuntime(692): at dalvik.system.NativeStart.main(Native Method)
04-28 18:07:14.911: I/Process(692): Sending signal. PID: 692 SIG: 9
04-28 18:10:06.128: E/Trace(711): error opening trace file: No such file or directory (2)
04-28 18:10:07.179: D/dalvikvm(711): GC_FOR_ALLOC freed 43K, 2% free 10842K/11011K, paused 70ms, total 71ms
04-28 18:10:07.188: I/dalvikvm-heap(711): Grow heap (frag case) to 11.204MB for 614416-byte allocation
04-28 18:10:07.258: D/dalvikvm(711): GC_CONCURRENT freed 1K, 2% free 11441K/11655K, paused 28ms+14ms, total 71ms
04-28 18:10:07.318: D/dalvikvm(711): GC_FOR_ALLOC freed 0K, 2% free 11441K/11655K, paused 26ms, total 26ms
04-28 18:10:07.330: I/dalvikvm-heap(711): Grow heap (frag case) to 12.245MB for 1093136-byte allocation
04-28 18:10:07.461: D/dalvikvm(711): GC_CONCURRENT freed 0K, 2% free 12508K/12743K, paused 26ms+4ms, total 129ms
04-28 18:10:07.461: D/dalvikvm(711): WAIT_FOR_CONCURRENT_GC blocked 12ms
04-28 18:10:08.179: D/gralloc_goldfish(711): Emulator without GPU emulation detected.
04-28 18:10:30.158: D/AndroidRuntime(711): Shutting down VM
04-28 18:10:30.158: W/dalvikvm(711): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
04-28 18:10:30.168: E/AndroidRuntime(711): FATAL EXCEPTION: main
04-28 18:10:30.168: E/AndroidRuntime(711): java.lang.NullPointerException
04-28 18:10:30.168: E/AndroidRuntime(711): at com.example.database.DBUse$1.onClick(DBUse.java:94)
04-28 18:10:30.168: E/AndroidRuntime(711): at android.view.View.performClick(View.java:4084)
04-28 18:10:30.168: E/AndroidRuntime(711): at android.view.View$PerformClick.run(View.java:16966)
04-28 18:10:30.168: E/AndroidRuntime(711): at android.os.Handler.handleCallback(Handler.java:615)
04-28 18:10:30.168: E/AndroidRuntime(711): at android.os.Handler.dispatchMessage(Handler.java:92)
04-28 18:10:30.168: E/AndroidRuntime(711): at android.os.Looper.loop(Looper.java:137)
04-28 18:10:30.168: E/AndroidRuntime(711): at android.app.ActivityThread.main(ActivityThread.java:4745)
04-28 18:10:30.168: E/AndroidRuntime(711): at java.lang.reflect.Method.invokeNative(Native Method)
04-28 18:10:30.168: E/AndroidRuntime(711): at java.lang.reflect.Method.invoke(Method.java:511)
04-28 18:10:30.168: E/AndroidRuntime(711): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-28 18:10:30.168: E/AndroidRuntime(711): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-28 18:10:30.168: E/AndroidRuntime(711): at dalvik.system.NativeStart.main(Native Method)
04-28 18:10:32.229: I/Process(711): Sending signal. PID: 711 SIG: 9