我是Java新手并试图为我和我的朋友玩的视频游戏构建一个配套应用程序（第一个应用程序！）。有了这个应用程序，我已经构建了一个包含多个表的SQLite数据库，并尝试调用它，查询它，并将这些数据显示在表中。
我的问题： 已编辑
我创建了一个外部SQLite数据库并将其复制到我的/ assets / databases /文件夹中。在研究我发现大多数人都说你必须将它复制到/ data / data / Package / databases位置才能真正使用它。
尝试访问我的数据时，我收到的表格不存在＆＃34;错误仅如果我告诉它抓取数据。如果我删除了调用我的数据的部分，应用程序加载正常并移动到活动正常，但如果我无法提取数据则无用。
E/AndroidRuntime: FATAL EXCEPTION: main
Process: info.ndakgamers.monsterdatabasetrial, PID: 17209
java.lang.RuntimeException: Unable to start activity ComponentInfo{info.ndakgamers.monsterdatabasetrial/info.ndakgamers.monsterdatabasetrial.Anjanath}: android.database.sqlite.SQLiteException: no such table: lrgmonsters (code 1): , while compiling: SELECT monstername, element, ailments, weakness, resistances, locations FROM lrgmonsters WHERE MonsterName = 'Anjanath'
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: android.database.sqlite.SQLiteException: no such table: lrgmonsters (code 1): , while compiling: SELECT monstername, element, ailments, weakness, resistances, locations FROM lrgmonsters WHERE MonsterName = 'Anjanath'
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
现在，在任何人提起之前，我已经在互联网上搜索过了。我已经阅读了很多博客和主题等等，而且我想知道我需要通过多少工作才能让SQLite数据库在应用程序中运行。
我已经准备好了："Using your own SQLite database in Android applications"
这就是我用来复制＆＃39;我的SQLite数据库在内部，所以我可以在应用程序中使用它来查询我的数据。
以下是我的项目：
TestDataHelper.java
package info.ndakgamers.monsterdatabasetrial;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
public class TestDataHelper extends SQLiteOpenHelper {
//Setting our SQL KEYS
public static final String KEY_ID = "_id";
public static final String KEY_MONSTERNAME = "monstername";
public static final String KEY_ELEMENT = "element";
public static final String KEY_AILMENTS = "ailments";
public static final String KEY_WEAKNESS = "weakness";
public static final String KEY_RESISTANCES = "resistances";
public static final String KEY_LOCATIONS = "locations";
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/info.ndakgamers.monsterdatabasetrial/databases/";
private static String DB_NAME = "MHWResearchData.db";
private static String DB_TABLE_NAME = "large_monsters";
private SQLiteDatabase myDataBase;
private final Context myContext;
private TestDataHelper testhelper;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
*
* @param context
*/
public String gettestData(){
String[] columns = new String[]{KEY_ID, KEY_MONSTERNAME, KEY_ELEMENT, KEY_AILMENTS, KEY_WEAKNESS, KEY_RESISTANCES, KEY_LOCATIONS};
//Cursor cursor = myDataBase.rawQuery("SELECT * FROM large_monsters WHERE monstername = 'Anjanath'",null);
Cursor cursor = myDataBase.query(DB_TABLE_NAME, columns, KEY_MONSTERNAME, null, null, null, null);
String result = "";
int iMonsterName = cursor.getColumnIndex(KEY_MONSTERNAME);
int iElement = cursor.getColumnIndex(KEY_ELEMENT);
int iAilments = cursor.getColumnIndex(KEY_AILMENTS);
int iWeakness = cursor.getColumnIndex(KEY_WEAKNESS);
int iResistances = cursor.getColumnIndex(KEY_RESISTANCES);
int iLocations = cursor.getColumnIndex(KEY_LOCATIONS);
for (cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()){
result = result + cursor.getString(iMonsterName) + " "
+ cursor.getString(iElement) + " "
+ cursor.getString(iAilments) + " "
+ cursor.getString(iWeakness) + " "
+ cursor.getString(iResistances) + " "
+ cursor.getString(iLocations) + "\n";
}
return result;
}
public TestDataHelper(Context context) {
super(context, DB_NAME, null, 2);
this.myContext = context;
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
*
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
//database does't exist yet.
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transfering bytestream.
*/
private void copyDataBase() throws IOException {
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
/**
* Creates a empty database on the system and rewrites it with your own database.
*/
public void createDatabase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
//do nothing - database already exist
} else {
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
// Add your public helper methods to access and get content from the database.
// You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
// to you to create adapters for your views.
}
Anjanath.java 我的数据抓取位置
package info.ndakgamers.monsterdatabasetrial;
import android.database.SQLException;
import android.database.sqlite.SQLiteException;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.GridView;
import android.widget.TextView;
import java.io.IOException;
public class Anjanath extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_anjanath);
TestDataHelper myDbHelper = new TestDataHelper(null);
myDbHelper = new TestDataHelper(this);
try {
myDbHelper.createDatabase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
TextView tvv = (TextView) findViewById(R.id.tvSQLInfo);
myDbHelper.openDataBase();
String newData = myDbHelper.gettestData();
myDbHelper.close();
tvv.setText(newData);
}catch(SQLiteException sqle){
throw sqle;
}
}
}
的 MainActivity.java
package info.ndakgamers.monsterdatabasetrial;
import android.app.Dialog;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
Button anjabtn;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
anjabtn = (Button) findViewById(R.id.anjabtn);
anjabtn.setOnClickListener(this);
}
@Override
public void onClick(View myview) {
switch (myview.getId()) {
case R.id.anjabtn:
boolean testItem = true;
try {
Intent anjIntent = new Intent("info.ndakgamers.monsterdatabasetrial.ANJANATH");
startActivity(anjIntent);
}catch(Exception excep) {
testItem = false;
}finally {
if (testItem) {
Dialog dworks = new Dialog(this);
TextView tv = new TextView(this);
tv.setText("Success");
dworks.setContentView(tv);
dworks.show();
}else {
Dialog dfails = new Dialog(this);
TextView tv = new TextView(this);
tv.setText("Failure");
dfails.setContentView(tv);
dfails.show();
}
}
break;
}
}
}
Anjanath XML，如果有人好奇并希望帮助我将每个SQLite列排序到每列
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
tools:context="info.ndakgamers.monsterdatabasetrial.Anjanath">
<ImageView
android:id="@+id/anjaBanner"
android:layout_width="320dp"
android:layout_height="144dp"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0"
app:srcCompat="@drawable/anjanath_render" />
<HorizontalScrollView
android:layout_width="match_parent"
android:layout_height="match_parent">
<TableLayout
android:layout_width="wrap_content"
android:layout_height="match_parent">
<TableRow
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/tblMonsterNames"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="Monster Names"
android:textAlignment="center" />
<TextView
android:id="@+id/tblElement"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="Element"
android:textAlignment="center" />
<TextView
android:id="@+id/tblAilments"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="Ailments"
android:textAlignment="center" />
<TextView
android:id="@+id/tblWeakness"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="Weakness"
android:textAlignment="center" />
<TextView
android:id="@+id/tblResistances"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="Resistances"
android:textAlignment="center" />
<TextView
android:id="@+id/tblLocations"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="Locations"
android:textAlignment="center" />
</TableRow>
<TableRow
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:id="@+id/tvSQLInfo"
android:layout_width="361dp"
android:layout_height="61dp"
android:text="db Data Goes Here"
tools:layout_editor_absoluteX="12dp"
tools:layout_editor_absoluteY="163dp" />
</TableRow>
</TableLayout>
</HorizontalScrollView>
</LinearLayout>
答案 0 :(得分：0)
你的助手的onCreate是空的！这意味着您不会创建任何表。您应该为放入数据库的每个tabel创建一个带CREATE TABLE语句的查询，并在helper的onCreate中执行所有这些查询。
另外，既然您已经提到了编写所有这些代码所需的辛勤工作，我建议您查看Room Persistence Library，它会对您有所帮助！
答案 1 :(得分：0)
我认为您的问题是您已将文件复制到 / assets / databases / 但只是使用数据库名称，而您需要在打开时包含数据库子目录文件。而不是
InputStream myInput = myContext.getAssets().open(DB_NAME);
你需要使用： -
InputStream myInput = myContext.getAssets().open("databases/" + DB_NAME);
或者将文件复制到assets文件夹而不是数据库子目录。