我在 android 2.2 中运行一个程序。我收到一个错误应用程序意外停止然后强制关闭。我一次又一次地清理项目然后构建，但问题仍然存在。
ApplicationContextProvider.java
package com.android.tuts;
import android.app.Application;
import android.content.Context;
public class ApplicationContextProvider extends Application{
private static Context sContext;
@Override
public void onCreate() {
super.onCreate();
sContext = getApplicationContext();
}
public static Context getContext() {
return sContext;
}
}
数据库管理.java
package com.android.tuts;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class DataBaseManager extends SQLiteOpenHelper {
// The Android's default system path of your application database.
//data/data/ and /databases remain the same always. The one that must be changed is com.example which represents
//the MAIN package of your project
private static String DB_PATH = "/data/data/com.android/databases/";
//the name of your database
private static String DB_NAME = "database";
private static SQLiteDatabase mDataBase;
private static DataBaseManager sInstance = null;
// database version
private static final int DATABASE_VERSION = 1;
/**
* Constructor Takes and keeps a reference of the passed context in order to
* access to the application assets and resources.
*/
private DataBaseManager() {
super(ApplicationContextProvider.getContext(), DB_NAME, null, DATABASE_VERSION);
try {
createDataBase();
openDataBase();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* Singleton for DataBase
*
* @return singleton instance
*/
public static DataBaseManager instance() {
if (sInstance == null) {
sInstance = new DataBaseManager();
}
return sInstance;
}
/**
* Creates a empty database on the system and rewrites it with your own
* database.
*
* @throws java.io.IOException io exception
*/
private void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
// do nothing - database already exist
} else {
// By calling this method an 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");
}
}
}
/**
* 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 doesn'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.
*
* @throws java.io.IOException io exception
*/
public void copyDataBase() throws IOException {
// Open your local db as the input stream
InputStream myInput = ApplicationContextProvider.getContext().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();
}
private void openDataBase() throws SQLException {
// Open the database
String myPath = DB_PATH + DB_NAME;
mDataBase = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
}
/**
* Select method
*
* @param query select query
* @return - Cursor with the results
* @throws android.database.SQLException sql exception
*/
public Cursor select(String query) throws SQLException {
return mDataBase.rawQuery(query, null);
}
/**
* Insert method
*
* @param table - name of the table
* @param values values to insert
* @throws android.database.SQLException sql exception
*/
public void insert(String table, ContentValues values) throws SQLException {
mDataBase.insert(table, null, values);
}
/**
* Delete method
*
* @param table - table name
* @param where WHERE clause, if pass null, all the rows will be deleted
* @throws android.database.SQLException sql exception
*/
public void delete(String table, String where) throws SQLException {
mDataBase.delete(table, where, null);
}
/**
* Update method
*
* @param table - table name
* @param values - values to update
* @param where - WHERE clause, if pass null, all rows will be updated
*/
public void update(String table, ContentValues values, String where) {
mDataBase.update(table, values, where, null);
}
/**
* Let you make a raw query
*
* @param command - the sql comand you want to run
*/
public void sqlCommand(String command) {
mDataBase.execSQL(command);
}
@Override
public synchronized void close() {
if (mDataBase != null)
mDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
我的活动.java
package com.android.tuts;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MyActivity extends Activity {
private DataBaseManager dataBase;
private Button insertButton;
private Button updateButton;
private Button deleteButton;
private TextView textView;
//put the table name and column in constants
public static final String TABLE_NAME = "People";
public static final String COLUMN_NAME = "name";
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
dataBase = DataBaseManager.instance();
textView = (TextView)findViewById(R.id.name_1);
insertButton = (Button)findViewById(R.id.insert);
updateButton = (Button)findViewById(R.id.update);
deleteButton = (Button)findViewById(R.id.delete);
insertButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//with ContentValues put the data we want into the database
ContentValues values = new ContentValues();
values.put(COLUMN_NAME, "Diana");
//here we insert the data we have put in values
dataBase.insert(TABLE_NAME, values);
updateTextView();
}
});
updateButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//with ContentValues put the data we want into the database
ContentValues values = new ContentValues();
values.put(COLUMN_NAME,"George");
//here we replace the record which has the _id=1 with the given name in the values "George"
dataBase.update(TABLE_NAME, values, "_id=1");
updateTextView();
}
});
deleteButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//here we delete the record which has the "name=George"
dataBase.delete(TABLE_NAME,"name='George'");
updateTextView();
}
});
}
@SuppressWarnings("null")
public void updateTextView(){
//to get data from database we need a cursor.
//after we perform a select query all the data from database specific for the query, will be in the cursor
// "*" means "all" in translation the query means "SELECT ALL FROM NAME TABLE"
Cursor cursor = dataBase.select("SELECT * FROM " + TABLE_NAME);
//here we verify the cursor for null. If is null then the cursor must be closed.
//Once you open a cursor you have to close it too after you don't use it
if (cursor == null){
cursor.close();
}
textView.setText("");
//the cursor iterates the column "name"
while (cursor.moveToNext()){
//in this string we get the record for each row from the column "name"
String s = cursor.getString(cursor.getColumnIndex(COLUMN_NAME));
//in this textView will be added, updated or deleted the string
// "\n" means "new line"
textView.append("\n" + s);
}
//here we close the cursor because we do not longer need it
cursor.close();
}
}
显现
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.android.tuts"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" />
<application android:name=".ApplicationContextProvider" android:label="@string/app_name">
<activity android:name=".MyActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>