android - 在不使用主键的情况下查询 android sqlite 数据库会引发错误 java.lang.NullPointerException

Question

我在 android 中开发了一个地图应用程序，它根据用户的搜索输入在数据库中搜索地点。我试图使用一个字段来查询 sqlite 数据库，该字段将在数据库中搜索并返回所有在数据库中的地方的纬度。该字段不是下面的主键是代码。请我需要帮助。用于创建和访问数据库的数据库类。

public class Places {
private Context context;
private DbHelper dataHelper;
private SQLiteDatabase database;

//columns for places table
public static final String ROW_ID="_id";
public static final String P_NAME="placename";
public static final String G_NAME="genericname";
public static final String LONGITUDE="longitude";
public static final String LATITUDE="latitude";
public static final String CONTACT="contactnumbers";



private static final String DB_NAME="MAP.db";
private static final String DB_TABLE_PLACES="places";
private static final String DB_TABLE_EXAMS="exam";
private static final String DB_TABLE_SMS="message";
private static final int DB_VERSION= 1;

// Places.java 的构造函数

 public Places(Context c){
     this.context = c;
 }

//数据库助手类

private static class DbHelper extends SQLiteOpenHelper  {


 //constructor for DbHelper inner class

public DbHelper(Context context) {
    super(context, DB_NAME, null, DB_VERSION);
    // TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db) {
    // TODO Auto-generated method stub
    //creating table PLACES
    db.execSQL("CREATE TABLE "+DB_TABLE_PLACES+"("+ROW_ID+" PRIMARY KEY, " +
            ""+P_NAME+" TEXT NOT NULL, " +
            ""+G_NAME+" TEXT NOT NULL, " +
            ""+LONGITUDE+" TEXT NOT NULL, " +
            ""+LATITUDE+" TEXT NOT NULL, " +
            ""+CONTACT+" TEXT );");



    @Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // TODO Auto-generated method stub
    db.execSQL("DROP TABLE IF EXISTS "+DB_TABLE_PLACES);
    db.execSQL("DROP TABLE IF EXISTS "+DB_TABLE_EXAMS);
    db.execSQL("DROP TABLE IF EXISTS "+DB_TABLE_SMS);

    onCreate(db);
}

}

  public Places openDatabase() throws SQLiteException{
   dataHelper = new DbHelper(context);
   database= dataHelper.getWritableDatabase();
return this;

}

  public void closeDatabase(){
dataHelper.close();
database.close();

}

@SuppressWarnings("null")
 public List<String> getPlaceLatitude(String string) {
// TODO Auto-generated method stub

List<String> latitudes = null;
String[] columns= new String[]{ROW_ID,P_NAME,LATITUDE,LONGITUDE,G_NAME,CONTACT};

Cursor c = database.query(DB_TABLE_PLACES, columns,G_NAME+" = "+string, null, null, null, null);

int iLatitude = c.getColumnIndex(LATITUDE);
if (c !=null){
for(c.moveToFirst();!c.isAfterLast();c.moveToNext()){
    latitudes.add(c.getString(iLatitude));
}
}
return latitudes;}

触发操作以查询数据库的方法。

public void searchDbAndOpenIntent(String search){
try{
        Places placeDb = new Places(this);
        placeDb.openDatabase();
        List<String> longitude1= placeDb.getPlaceLongitude(search);
                List<String> latitude1=placeDb.getPlaceLatitude(search);
        placeDb.closeDatabase();
}
                  catch (Exception e) {
            // TODO:handle exception                                    Toast.makeText(getBaseContext(),e.toString(),Toast.LENGTH_LONG).show();
        }
}




public void searchDbAndOpenIntent(String search){
try{
        Places placeDb = new Places(this);
        placeDb.openDatabase();
        List<String> longitude1= placeDb.getPlaceLongitude(search);
                List<String> latitude1=placeDb.getPlaceLatitude(search);
        placeDb.closeDatabase();



        }
                  catch (Exception e) {
            // TODO: handle exception


            Toast.makeText(getBaseContext(), e.toString(), Toast.LENGTH_LONG).show();
        }
}

请我想根据地点的通用名称返回纬度，但是当我尝试查询 generic_name 列时，它返回 java.lang.NullPointerexception 。在它下面是当按下查询数据库的按钮时我得到的日志猫

       05-14 20:52:37.202: D/ddm-heap(243): Got feature list request
       05-14 20:52:41.123: E/ActivityThread(243): Failed to find provider info for       com.google.settings
       05-14 20:52:41.132: E/ActivityThread(243): Failed to find provider info for   com.google.settings
       05-14 20:52:41.172: E/ActivityThread(243): Failed to find provider info for com.google.settings
       05-14 20:52:41.562: D/dalvikvm(243): GC freed 2007 objects / 134424 bytes in 125ms
       05-14 20:52:41.802: D/LocationManager(243): Constructor: service =   android.location.ILocationManager$Stub$Proxy@44e8c078
       05-14 20:52:42.012: I/MapActivity(243): Handling network change  notification:CONNECTED
       05-14 20:52:42.012: E/MapActivity(243): Couldn't get connection factory client
       05-14 20:52:42.453: D/dalvikvm(243): GC freed 4934 objects / 288736 bytes in 136ms
       05-14 20:52:48.852: D/dalvikvm(243): GC freed 10599 objects / 817800 bytes in  137ms
       05-14 20:53:56.712: W/KeyCharacterMap(243): No keyboard for id 0
       05-14 20:53:56.723: W/KeyCharacterMap(243): Using default keymap: /system /usr/keychars/qwerty.kcm.bin
       05-14 20:53:59.712: D/LocationManager(243): removeUpdates: listener =  my.project.success.KnustP2PActivity@44e93c70
       05-14 20:54:11.812: D/dalvikvm(243): GC freed 5940 objects / 725376 bytes in 98ms
       05-14 20:54:11.812: I/dalvikvm(243): Uncaught exception thrown by finalizer (will be discarded):
       05-14 20:54:11.812: I/dalvikvm(243): Ljava/lang/IllegalStateException;:  Finalizing cursor android.database.sqlite.SQLiteCursor@44f31670 on places that has not  been deactivated or closed
       05-14 20:54:11.812: I/dalvikvm(243):     at android.database.sqlite.SQLiteCursor.finalize(SQLiteCursor.java:596)
       05-14 20:54:11.822: I/dalvikvm(243):     at dalvik.system.NativeStart.run(Native Method)
       05-14 20:54:11.872: E/Database(243): Leak found
       05-14 20:54:11.872: E/Database(243): java.lang.IllegalStateException: /data/data/my.project.success/databases/MAP.db SQLiteDatabase created and never closed
       05-14 20:54:11.872: E/Database(243):     at android.database.sqlite.SQLiteDatabase.<init>(SQLiteDatabase.java:1694)
       05-14 20:54:11.872: E/Database(243):     at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:738)
       05-14 20:54:11.872: E/Database(243):     at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:760)
       05-14 20:54:11.872: E/Database(243):     at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:753)
       05-14 20:54:11.872: E/Database(243):     at android.app.ApplicationContext.openOrCreateDatabase(ApplicationContext.java:473)
       05-14 20:54:11.872: E/Database(243):     at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:193)
       05-14 20:54:11.872: E/Database(243):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
       05-14 20:54:11.872: E/Database(243):     at my.project.success.Places.openDatabase(Places.java:201)
       05-14 20:54:11.872: E/Database(243):     at my.project.success.SearchActivity.searchDbAndOpenIntent(SearchActivity.java:217)
       05-14 20:54:11.872: E/Database(243):     at my.project.success.SearchActivity.onClick(SearchActivity.java:151)
       05-14 20:54:11.872: E/Database(243):     at android.view.View.performClick(View.java:2364)
       05-14 20:54:11.872: E/Database(243):     at android.view.View.onTouchEvent(View.java:4179)
       05-14 20:54:11.872: E/Database(243):     at android.widget.TextView.onTouchEvent(TextView.java:6540)
       05-14 20:54:11.872: E/Database(243):     at android.view.View.dispatchTouchEvent(View.java:3709)
       05-14 20:54:11.872: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:11.872: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:11.872: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:11.872: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:11.872: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:11.872: E/Database(243):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1659)
       05-14 20:54:11.872: E/Database(243):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1107)
       05-14 20:54:11.872: E/Database(243):     at android.app.Activity.dispatchTouchEvent(Activity.java:2061)
       05-14 20:54:11.872: E/Database(243):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1643)
       05-14 20:54:11.872: E/Database(243):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1691)
       05-14 20:54:11.872: E/Database(243):     at android.os.Handler.dispatchMessage(Handler.java:99)
       05-14 20:54:11.872: E/Database(243):     at android.os.Looper.loop(Looper.java:123)
       05-14 20:54:11.872: E/Database(243):     at     android.app.ActivityThread.main(ActivityThread.java:4363)
       05-14 20:54:11.872: E/Database(243):     at java.lang.reflect.Method.invokeNative(Native Method)
       05-14 20:54:11.872: E/Database(243):     at java.lang.reflect.Method.invoke(Method.java:521)
       05-14 20:54:11.872: E/Database(243):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
       05-14 20:54:11.872: E/Database(243):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
       05-14 20:54:11.872: E/Database(243):     at dalvik.system.NativeStart.main(Native Method)
       05-14 20:54:12.014: I/dalvikvm(243): Uncaught exception thrown by finalizer (will be discarded):
       05-14 20:54:12.022: I/dalvikvm(243): Ljava/lang/IllegalStateException;: Finalizing cursor  android.database.sqlite.SQLiteCursor@44f2f0b0 on places that has not been deactivated or closed
       05-14 20:54:12.022: I/dalvikvm(243):     at android.database.sqlite.SQLiteCursor.finalize(SQLiteCursor.java:596)
       05-14 20:54:12.032: I/dalvikvm(243):     at dalvik.system.NativeStart.run(Native Method)
       05-14 20:54:12.152: E/Database(243): Leak found
       05-14 20:54:12.152: E/Database(243): java.lang.IllegalStateException: /data/data/my.project.success/databases/MAP.db SQLiteDatabase created and never closed
       05-14 20:54:12.152: E/Database(243):     at android.database.sqlite.SQLiteDatabase.<init>(SQLiteDatabase.java:1694)
       05-14 20:54:12.152: E/Database(243):     at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:738)
       05-14 20:54:12.152: E/Database(243):     at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:760)
       05-14 20:54:12.152: E/Database(243):     at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:753)
       05-14 20:54:12.152: E/Database(243):     at android.app.ApplicationContext.openOrCreateDatabase(ApplicationContext.java:473)
       05-14 20:54:12.152: E/Database(243):     at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:193)
       05-14 20:54:12.152: E/Database(243):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
       05-14 20:54:12.152: E/Database(243):     at my.project.success.Places.openDatabase(Places.java:201)
       05-14 20:54:12.152: E/Database(243):     at my.project.success.SearchActivity.searchDbAndOpenIntent(SearchActivity.java:217)
       05-14 20:54:12.152: E/Database(243):     at my.project.success.SearchActivity.onClick(SearchActivity.java:79)
       05-14 20:54:12.152: E/Database(243):     at android.view.View.performClick(View.java:2364)
       05-14 20:54:12.152: E/Database(243):     at android.view.View.onTouchEvent(View.java:4179)
       05-14 20:54:12.152: E/Database(243):     at android.widget.TextView.onTouchEvent(TextView.java:6540)
       05-14 20:54:12.152: E/Database(243):     at android.view.View.dispatchTouchEvent(View.java:3709)
       05-14 20:54:12.152: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:12.152: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:12.152: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:12.152: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:12.152: E/Database(243):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
       05-14 20:54:12.152: E/Database(243):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1659)
       05-14 20:54:12.152: E/Database(243):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1107)
       05-14 20:54:12.152: E/Database(243):     at android.app.Activity.dispatchTouchEvent(Activity.java:2061)
       05-14 20:54:12.152: E/Database(243):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1643)
       05-14 20:54:12.152: E/Database(243):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1691)
       05-14 20:54:12.152: E/Database(243):     at android.os.Handler.dispatchMessage(Handler.java:99)
       05-14 20:54:12.152: E/Database(243):     at android.os.Looper.loop(Looper.java:123)
       05-14 20:54:12.152: E/Database(243):     at android.app.ActivityThread.main(ActivityThread.java:4363)
       05-14 20:54:12.152: E/Database(243):     at java.lang.reflect.Method.invokeNative(Native Method)
       05-14 20:54:12.152: E/Database(243):     at java.lang.reflect.Method.invoke(Method.java:521)
       05-14 20:54:12.152: E/Database(243):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
       05-14 20:54:12.152: E/Database(243):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
       05-14 20:54:12.152: E/Database(243):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

您需要string在查询中将变量括在单引号中。

它应该如下所示：

G_NAME+" = '" + string + "'"

编辑

这是不正确的，因为您尝试访问游标而不首先移动到第一条记录：

int iLatitude = c.getColumnIndex(LATITUDE);
if (c !=null){
for(c.moveToFirst();!c.isAfterLast();c.moveToNext()){
    latitudes.add(c.getString(iLatitude));
}

试试这个：

c.moveToFirst();
int iLatitude = c.getColumnIndex(LATITUDE);
if (c !=null){
    while(c.isAfterLast == false){
        latitudes.add(c.getString(iLatitude));
        c.moveToNext();
    }
}

这也会改变你的循环，主要是为了可读性。