我有一个带有“主要”活动的应用，该活动有8个子活动。在主要活动中，我从数据库中读取并将有关所选项目（通过微调器）的基本信息加载到一个包中（这样每个活动都可以加载更快，因为我不需要在onCreate方法中查询数据库用于创建视图的活动）。在新活动中创建视图后，我向DB查询该特定活动所需的剩余数据。在此之前，我使用了公共变量，它允许我的databasehelper类知道要查看哪个表来获取数据。我知道你不应该如何编程，所以我将我的应用程序转换为使用捆绑包（不确定它是否是最佳方式，但我相信它是朝着正确方向迈出的一步）。
我目前能够在我的所有8个子活动中访问保存到该捆绑包中的数据，但我无法从我的databasehelper类访问它。
我在主要活动中使用的捆绑包：
bundle = new Bundle();
bundle.putString("KEY_tableName", tableName);
bundle.putInt("KEY_numOne", numOne);
bundle.putInt("KEY_numTwo", numTwo);
... and others
my databasehelper class ：
package com.myName.myAPP;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
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.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DataBaseHelper extends SQLiteOpenHelper {
//The Android's default system path of your application database.
static String DB_PATH = "/data/data/com.myName.myApp/databases/";
static String DB_NAME = "databasefile";
public SQLiteDatabase myDataBase;
private final Context myContext;
//version of database
private static final int version = 1;
public static final String KEY_ROWID = "_id";
public static final String KEY_TITLE = "Title";
public static final String KEY_BODY = "Content";
public static final String KEY_DATE = "Date";
private static final String TAG = "NotesDbAdapter";
//private static final String DATABASE_CREATE = "create table notes (_id integer primary " +
// "key autoincrement, " + "title text not null, body text not null);";
//private static final String DATABASE_TABLE = "notes";
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
DataBaseHelper(Context context) {
super(context, DB_NAME, null, version);
this.myContext = context;
}
/**
* 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
} // end if
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(myContext);
} // end try
catch (IOException e) {
throw new Error("Error copying database");
} // end catch
} // end else
this.close();
} // end createDataBase()
/**
* 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);
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
//File dbFile = new File(DB_PATH + DB_NAME);
//return dbFile.exists();
}
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(Context myContext) throws IOException {
File fileTest = myContext.getFileStreamPath(DB_NAME);
boolean exists = fileTest.exists();
if (!exists) {
// Open the empty db as the output stream
OutputStream databaseOutputStream = new FileOutputStream(DB_PATH + DB_NAME);
InputStream databaseInputStream;
databaseInputStream = myContext.getAssets().open(DB_NAME);
byte[] buffer = new byte[1024];
@SuppressWarnings("unused")
int length;
while ((length = databaseInputStream.read(buffer)) > 0) {
databaseOutputStream.write(buffer);
} // end while
databaseInputStream.close();
databaseInputStream = myContext.getAssets().open(DB_NAME);
while ((length = databaseInputStream.read(buffer)) > 0) {
databaseOutputStream.write(buffer);
} // end while
// Close the streams
databaseInputStream.close();
databaseOutputStream.flush();
databaseOutputStream.close();
} // end if
} // end copyDataBase
public void openDataBase() throws SQLException{
File f = new File(DB_PATH);
if (!f.exists()) {
f.mkdir();
}
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
} // end openDataBase
@Override
public void close() {
if(myDataBase != null) {
myDataBase.close();
}
super.close();
} // end close
@Override
public void onCreate(SQLiteDatabase db) {
} // end onCreate
@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 notes");
onCreate(db);
} // end onUpgrade
另外，我还有其他方法可以读取/写入/更新数据库。
在我的孩子活动中，我通过调用：
来访问该包String tableName = getIntent().getExtras().getString("KEY_tableName");
int numOne = getIntent().getExtras().getString("KEY_numOne");
...
在该活动的onCreate方法中能够使用数据
然而，当我在我的databasehelper类的方法中使用该代码时，我得到一个错误：getIntent（），它将无法在android studio中编译。错误是：
java: cannot find symbol
symbol: method getIntent()
location: class com.myName.myAPP.DataBaseHelper
谢谢你的帮助。
答案 0 :(得分：1)
getIntent()是一种Avctivity方法，因此无法在非Activity类中使用。
返回启动此活动的意图
但您不在Activity，因此无法识别
您需要创建一个构造函数来接受数据库所需的值，或创建接受这些值的方法并从Activities发送它们