【发布时间】：2018-12-21 15:13:22
【问题描述】：
我使用的是外部 sqlite 数据库，而不是在我的 android studio 项目中创建一个，因为该数据库将包含一些已经填充的数据在里面。但我还必须插入更多数据。 当我插入任何新数据时，它会显示新数据，但是当我关闭我的 android 应用程序并再次打开以查看数据时，通过应用程序新插入的数据以某种方式删除，只有预填充的数据是显示。
我正在使用用于 sqlite 的 DB 浏览器来创建外部 sqlite 数据库并在其中预填充一些数据。在我的 android studio 项目中，我将这个数据库添加到我的 assets 文件夹中，并实现了 SQLiteOpenHelper 类来访问这个数据库。从数据库表中读取数据是成功的。现在，当我插入新数据时，我也可以临时读取新数据。暂时从某种意义上说，在我关闭我的应用程序后，新数据会丢失。
我的外部 sqlite 数据库的表：
CREATE TABLE `table_name` (
`Id` INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
`Content` TEXT NOT NULL
);
SQLiteOpenHelper 类：
public class ProcessExternalDBHelper {
private static final String DATABASE_NAME = "database_name.db";
private static final int DATABASE_VERSION = 1;
private static String DATABASE_PATH = "";
private static final String DATABASE_TABLE = "table_name";
private static final String KEY_ROWID = "Id";
private static final String KEY_CONTENT = "Content";
private ExternalDbHelper ourHelper;
private final Context ourContext;
private SQLiteDatabase ourDatabase;
private static class ExternalDbHelper extends SQLiteOpenHelper {
public ExternalDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
if (Build.VERSION.SDK_INT >= 17) {
DATABASE_PATH = context.getApplicationInfo().dataDir +
"/databases/";
} else {
DATABASE_PATH = "/data/data/" + context.getPackageName() +
"/databases/";
}
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int
newVersion) {
}
}
public ProcessExternalDBHelper(Context context) {
ourContext = context;
}
//for reading
public ProcessExternalDBHelper openRead() throws SQLException {
ourHelper = new ExternalDbHelper(ourContext);
ourDatabase = ourHelper.getReadableDatabase();
return this;
}
//for writing
public ProcessExternalDBHelper openWrite() throws SQLException{
ourHelper = new ExternalDbHelper(ourContext);
ourDatabase = ourHelper.getWritableDatabase();
return this;
}
public void close() {
if (ourHelper != null) {
ourHelper.close();
}
}
//Create database in activity
public void createDatabase() throws IOException {
createDB();
}
//Create db if not exists
private void createDB() {
boolean dbExists = checkDatabase();
if (!dbExists) {
openRead();
try {
this.close();
copyDatabase();
} catch (IOException ie) {
throw new Error("Error copying database");
}
}
}
private boolean checkDatabase() {
boolean checkDB = false;
try {
String myPath = DATABASE_PATH + DATABASE_NAME;
File dbfile = new File(myPath);
checkDB = dbfile.exists();
} catch (SQLiteException e) {
}
return checkDB;
}
private void copyDatabase() throws IOException {
InputStream myInput = null;
OutputStream myOutput = null;
String outFileName = DATABASE_PATH + DATABASE_NAME;
try {
myInput = ourContext.getAssets().open(DATABASE_NAME);
myOutput = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
myOutput.flush();
myOutput.close();
myInput.close();
} catch (IOException ie) {
throw new Error("Copydatabase() error");
}
}
//To show all available contents in my database
public List<Model> findallContents() {
List<Model> mContents = new ArrayList<>();
String[] columns = new String[]{KEY_CONTENT};
Cursor cursor = ourDatabase.query(DATABASE_TABLE, columns, null, null,
null, null, null);
int iContent = cursor.getColumnIndex(KEY_CONTENT);
for (cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext())
{
Model model= new Model();
model.setContent(cursor.getString(iContent));
mContents.add(model);
}
cursor.close();
return mContents;
}
public void addContent(String content) {
ContentValues contentValues = new ContentValues();
contentValues.put(KEY_CONTENT, content);
ourDatabase.insert(DATABASE_TABLE, null, contentValues);
ourDatabase.close();
}
}
我的 Model.java 类：
public class Model {
private String mContent;
public String getContent() {
return mContent;
}
public void setContent(String content) {
this.mContent = content;
}
}
最后是我读写数据的活动类：
public class MainActivity extends AppCompatActivity {
private EditText editText_Content;
private ImageButton imageButton_Save;
private List<Model> mContentsArrayList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ProcessExternalDBHelper myDbHelper = new ProcessExternalDBHelper(this);
try {
myDbHelper.createDatabase();
} catch (IOException ioe) {
throw new Error("Unable to CREATE DATABASE");
} finally {
myDbHelper.close();
}
initialize();
GetContents();
imageButton_Save.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (!(editText_Content.getText().toString().trim().isEmpty()))
{
SaveContents();
}
}
});
}
private void initialize() {
editText_Content = findViewById(R.id.editText_contents);
imageButton_Save = findViewById(R.id.imageButton_save);
mContentsArrayList = new ArrayList<>();
}
//GetContents and show them later in my RecyclerView
private void GetContents() {
try {
mContentsArrayList.clear();
ProcessExternalDBHelper autoProcess = new
ProcessExternalDBHelper(this);
autoProcess.openRead();
mContentsArrayList.addAll(autoProcess.findallContents();
autoProcess.close();
} catch (Exception e) {
}
}
//For saving content into database
private void SaveContents() {
String content = editText_Content.getText().toString();
try {
ProcessExternalDBHelper autoProcess = new
ProcessExternalDBHelper(this);
autoProcess.openWrite(); //for writing into database
autoProcess.addContent(content);
autoProcess.close();
editText_Content.getText().clear();
} catch (Exception e) {
}
}
}
最后我正在使用 DB Browser for Sqlite (ver 3.10.1), android studio (ver 3.0.1), minSdkVersion 19.
我希望新插入到数据库中的数据能够被保存并在以后看到，即使我关闭我的应用程序并稍后重新启动应用程序也是如此。 谢谢！
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