我正在创建一个在assets文件夹中检索sqlite数据库的应用程序。当我运行程序时，在编译SELECT * FROM students时，它说没有这样的表:students。资产文件夹中有学生。Sqlite和有一个名为students的表，它由id、姓名和性别组成。我将在下面显示代码。
DatabaseHelper类
public class DatabaseHelper extends SQLiteOpenHelper {
private static String DB_PATH = "/data/data/com.example.user.students/databases/";
private static String DB_NAME = "students.sqlite";
private SQLiteDatabase myDataBase;
private Context myContext = null;
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
public void createDataBase() throws IOException {
boolean dbExist = this.checkDataBase();
if (!dbExist) {
this.getReadableDatabase();
try {
this.copyDataBase();
} catch (IOException e) {
throw new Error("Error");
}
}
}
public void copyDataBase() throws IOException {
InputStream myInput = this.myContext.getAssets().open(DB_NAME);
String outFileName = DB_PATH + DB_NAME;
FileOutputStream 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();
}
public boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String e = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(e, null, 0);
} catch (SQLiteException e) {
;
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null;
}
public void openDataBase() throws SQLException {
String myPath = DB_PATH + DB_NAME;
this.myDataBase = SQLiteDatabase.openDatabase(myPath, null, 0);
}
public synchronized void close() {
if (this.myDataBase != null) {
this.myDataBase.close();
}
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public List<Students> getAll() {
List<Students> sList = new ArrayList<Students>();
{
String selectQuery =
"SELECT * FROM students";
Log.e("students query: ", selectQuery);
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Students si = new Students();
si.setid(Integer.parseInt(cursor.getString(0)));
si.setname(cursor.getString(1));
si.setgender(cursor.getString(2));
sList.add(si);
} while (cursor.moveToNext());
}
db.close();
}
return sList;
}
}
学生类
public class Students {
//private variables
int id;
String name;
String gender;
// Empty constructor
public Students(){
}
// constructor
public Students(int id, String name, String gender){
this.id = id;
this.name = name;
this.gender = gender;
}
// getting ID
public int getid(){
return this.id;
}
// setting id
public void setid(int id){
this.id = id;
}
// getting name
public String getname(){
return this.name;
}
// setting name
public void setname(String name){
this.name = name;
}
// getting gender
public String getgender(){
return this.gender;
}
// setting gender
public void setgender(String gender){
this.gender = gender;
}
}
主活动类
public class MainActivity extends Activity {
List<Students> GetAll;
DatabaseHelper db = new DatabaseHelper(this);
Context context = this;
ListView list_doctors;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
list_students = (ListView) findViewById(R.id.list);
GetAll = db.getAll();
list_students.setAdapter(new ViewAdapter());
}
public class ViewAdapter extends BaseAdapter {
LayoutInflater mInflater;
public ViewAdapter() {
mInflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return GetAll.size();
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_item,null);
}
final TextView names = (TextView) convertView.findViewById(R.id.name);
final TextView gender = (TextView) convertView.findViewById(R.id.gender);
names.setText(GetAll.get(position).getname());
gender.setText(GetAll.get(position).getgender());
return convertView;
}
}
}
尝试在MainActivity的onCreate()方法中添加以下行:
public class MainActivity extends AppCompatActivity {
ListView lv;
ArrayList<Students> GetAll;
DatabaseHelper dbhelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbhelper = new DatabaseHelper(MainActivity.this);
//Add below lines to your original code
try{
dbhelper.createDataBase();
}
catch(IOException e){
e.printStackTrace();
}
try {
dbhelper.openDataBase();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//Till here
GetAll = dbhelper.getAll();
lv = (ListView) findViewById(R.id.lv);
lv.setAdapter(new ViewAdapter());
}
基本上这两行添加了dbhelper.createDataBase() & dbhelper.openDatabase () 只需检查数据库是否已从资产文件夹复制。
如果createDatabase()方法发现数据库不存在于内部数据库路径(在您的情况下，它是/data/data/com.example.user.students/databases/)，那么它只是将数据库从资产文件夹复制到内部数据库位置，然后简单地调用OpenDatabase()将打开数据库进行所需的读取操作。
如果createDatabase()方法发现DB_PATH中已经存在数据库，则不执行方法的其余部分，然后简单地调用OpenDatabase()将打开数据库进行所需的读操作。
希望它能清除图片!!