我一直在阅读有关该问题的Stackoverflow上的很多帖子。几乎所有答案都是关于使用SQLiteOpenHelper类，这正是我正在做的事情。
我的问题是我有一个存储一些统计信息的数据库，我想在StatsActivity中输出统计信息。问题是我在MainActivity中为统计信息创建了一个数据库，我不知道如何在StatsActivity中访问它。
我试图在StatsDB中实例化StatsActivity的实例，因为它已在其他主题中被告知。 StatsDB是一个扩展SQLiteOpenHelper并表示统计数据库的类。
StatsActivity.java
public class StatsActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_stats);
StatsDB stats = new StatsDB(this);
Cursor curs = stats.getAllStats();
TextView created = (TextView) findViewById(R.id.TextView_Created_Counter);
TextView participated = (TextView) findViewById(R.id.TextView_Participated_Counter);
}
}
但是，我一直收到来自字符串Cursor curs = stats.getAllStats();的跟踪回溯的运行时错误：
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.kirill.myapplication/com.example.kirill.myapplication.StatsActivity}: android.database.sqlite.SQLiteException: no such table: StatsDatabase (code 1): , while compiling: SELECT _id, type, number FROM StatsDatabase
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2696)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2757)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:163)
at android.app.ActivityThread.main(ActivityThread.java:6237)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:877)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: android.database.sqlite.SQLiteException: no such table: StatsDatabase (code 1): , while compiling: SELECT _id, type, number FROM StatsDatabase
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889)
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500)
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1318)
at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1165)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1036)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1204)
at com.example.kirill.myapplication.StatsDB.getAllStats(StatsDB.java:65)
at com.example.kirill.myapplication.StatsActivity.onCreate(StatsActivity.java:23)
at android.app.Activity.performCreate(Activity.java:6847)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2649)
它表示没有名称为StatsDatabase的数据库，但我正在对其进行实施MainActivity：
MainActivity.java
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.mapButton:
Intent intentMap = new Intent(this, MapsActivity.class);
startActivity(intentMap);
break;
case R.id.settingsButton:
Intent intentSettings = new Intent(this, SettingsActivity.class);
startActivity(intentSettings);
break;
case R.id.statsButton:
Intent intentStats = new Intent(this, StatsActivity.class);
startActivity(intentStats);
break;
default:
break;
}
}
Button mapBtn;
Button statsBtn;
Button settingsBtn;
StatsDB stats;
LocationsDB locations;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
stats = new StatsDB(this);
locations = new LocationsDB(this);
mapBtn = (Button) findViewById(R.id.mapButton);
statsBtn = (Button) findViewById(R.id.statsButton);
settingsBtn = (Button) findViewById(R.id.settingsButton);
mapBtn.setOnClickListener(this);
statsBtn.setOnClickListener(this);
settingsBtn.setOnClickListener(this);
}
}
StatsDB.java
package com.example.kirill.myapplication;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
/**
* Created by kirill on 21.11.17.
*/
public class StatsDB extends SQLiteOpenHelper {
public static String DATABASE_STATS = "StatsDatabase";
private static int VERSION = 1;
public static final String FIELD_ROW_ID = "_id";
public static final String FIELD_TYPE = "type";
public static final String FIELD_NUMBER = "number";
private static final String DATABASE_TABLE = "stats";
private SQLiteDatabase statsDB;
public StatsDB(Context context) {
super(context, DATABASE_STATS, null, VERSION);
statsDB = getWritableDatabase();
ContentValues created = new ContentValues();
ContentValues participated = new ContentValues();
created.put(FIELD_TYPE, "Created");
created.put(FIELD_NUMBER, "0");
participated.put(FIELD_TYPE, "Participated");
participated.put(FIELD_NUMBER, "0");
statsDB.insert(DATABASE_TABLE, null, created);
statsDB.insert(DATABASE_TABLE, null, participated);
}
@Override
public void onCreate(SQLiteDatabase db) {
String sql = "create table " + DATABASE_TABLE + " ( " +
FIELD_ROW_ID + " integer primary key autoincrement , " +
FIELD_TYPE + " string , " +
FIELD_NUMBER + " int " +
" ) ";
db.execSQL(sql);
}
public long insert(ContentValues contentValues){
long rowID = statsDB.insert(DATABASE_TABLE, null, contentValues);
return rowID;
}
public int del(){
int cnt = statsDB.delete(DATABASE_TABLE, null , null);
return cnt;
}
public Cursor getAllStats(){
return statsDB.query(DATABASE_STATS, new String[] { FIELD_ROW_ID, FIELD_TYPE , FIELD_NUMBER} , null, null, null, null, null);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
LocationsDB.java
package com.example.kirill.myapplication;
/**
* Created by kirill on 21.11.17.
*/
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class LocationsDB extends SQLiteOpenHelper {
/** Database name */
private static String DATABASE_LOCATIONS = "locationmarkersqlite";
/** Version number of the database */
private static int VERSION = 1;
/** Field 1 of the table locations, which is the primary key */
public static final String FIELD_ROW_ID = "_id";
/** Field 2 of the table locations, stores the latitude */
public static final String FIELD_LAT = "lat";
/** Field 3 of the table locations, stores the longitude*/
public static final String FIELD_LNG = "lng";
/** Field 4 of the table locations, stores the zoom level of map*/
public static final String FIELD_ZOOM = "zom";
/** A constant, stores the the table name */
private static final String DATABASE_TABLE = "locations";
/** An instance variable for SQLiteDatabase */
private SQLiteDatabase mDB;
/** Constructor */
public LocationsDB(Context context) {
super(context, DATABASE_LOCATIONS, null, VERSION);
this.mDB = getWritableDatabase();
}
/** This is a callback method, invoked when the method getReadableDatabase() / getWritableDatabase() is called
* provided the database does not exists
* */
@Override
public void onCreate(SQLiteDatabase db) {
String sql = "create table " + DATABASE_TABLE + " ( " +
FIELD_ROW_ID + " integer primary key autoincrement , " +
FIELD_LNG + " double , " +
FIELD_LAT + " double , " +
FIELD_ZOOM + " text " +
" ) ";
db.execSQL(sql);
}
/** Inserts a new location to the table locations */
public long insert(ContentValues contentValues){
long rowID = mDB.insert(DATABASE_TABLE, null, contentValues);
return rowID;
}
/** Deletes all locations from the table */
public int del(){
int cnt = mDB.delete(DATABASE_TABLE, null , null);
return cnt;
}
/** Returns all the locations from the table */
public Cursor getAllLocations(){
return mDB.query(DATABASE_TABLE, new String[] { FIELD_ROW_ID, FIELD_LAT , FIELD_LNG, FIELD_ZOOM } , null, null, null, null, null);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
那么我在这种方法中做错了什么或者还有其他方法吗？
答案 0 :(得分：2)
statsDB.query(DATABASE_STATS ...你需要在那里使用表，而不是数据库
您的错误告诉您no such table: StatsDatabase，这是真的。您创建的表名为stats