Java 从片段访问 SQLite 数据库
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时间：2020-08-13 21:05:10 来源:igfitidea点击:
Accessing SQLite database from fragment
提问by evyamiz
My app contains MainActivity class and several fragments. One of the is the registration fragment which I want it to be able tho interact with my database which should contain only one table named USERS to whom I will CRUD. I've opened the MySQLiteOpenHelper class that extends SQLiteOpenHelper and created a User class as well. I've declared:
我的应用程序包含 MainActivity 类和几个片段。其中之一是我希望它能够与我的数据库交互的注册片段，该数据库应该只包含一个名为 USERS 的表，我将对其进行 CRUD。我打开了 MySQLiteOpenHelper 类，它扩展了 SQLiteOpenHelper 并创建了一个 User 类。我已经声明：
MySQLiteOpenHelper db = new MySQLiteOpenHelper(this);
in the activity's onCreate method. My question is how do I interact with this db from the fragments? I've tried the following code but it didn't work:
在活动的 onCreate 方法中。我的问题是如何与片段中的这个数据库交互？我已经尝试了以下代码，但没有奏效：
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
public class registration extends Fragment {
public registration() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.registration, container,
false);
return rootView;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
final EditText etFirstName = (EditText) getActivity().findViewById(
R.id.etFirstName);
final EditText etLastName = (EditText) getActivity().findViewById(
R.id.etLastName);
final EditText etEmail = (EditText) getActivity().findViewById(
R.id.etEmail);
final EditText etUsername = (EditText) getActivity().findViewById(
R.id.etUsername);
final EditText etPassword = (EditText) getActivity().findViewById(
R.id.etPassword);
Button bDone = (Button) getActivity().findViewById(R.id.bDone);
bDone.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
MySQLiteOpenHelper db = new MySQLiteOpenHelper(null);//do I need this??
db.addUser(new User(etFirstName.getText().toString(),
etLastName.getText().toString(), etEmail.getText()
.toString(), etUsername.getText().toString(),
etPassword.getText().toString()));
}
});
}
}
What happens now is that the moment I click the DONE button the app crushes... Thank's!!
现在发生的事情是，当我单击“完成”按钮时，应用程序崩溃了……谢谢！
MySQLiteOpenHelper looks like this:
MySQLiteOpenHelper 看起来像这样：
import java.util.LinkedList;
import java.util.List;
import android.R.string;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class MySQLiteOpenHelper extends SQLiteOpenHelper {
private static final int DATABASE_VERSION=1;
private static final String DATABASE_NAME="MyDB";
private static final String TABLE_USERS="USERS";
private static final String FIRST_NAME="First_name";
private static final String LAST_NAME="Last_name";
private static final String EMAIL="Email";
private static final String USERNAME="Username";
private static final String PASSWORD="Password";
private static final String COLUMNS[]={FIRST_NAME, LAST_NAME, EMAIL, USERNAME, PASSWORD};
public MySQLiteOpenHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
String CREATE_MyDB_TABLE = "CREATE TABLE USERS ( " +
"First_name TEXT, " +
"Last_name TEXT, "+
"Email KEY TEXT NOT NULL, "+
"Username TEXT NOT NULL, "+
"Password TEXT NOT NULL)";
db.execSQL(CREATE_MyDB_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS USERS");
this.onCreate(db);
}
public void addUser(User user){
Log.d("addUser", user.toString());
SQLiteDatabase db=this.getWritableDatabase();
ContentValues values=new ContentValues();
values.put(FIRST_NAME, user.getFirstName());
values.put(LAST_NAME, user.getLastName());
values.put(EMAIL, user.getEmail());
values.put(USERNAME, user.getUsername());
values.put(PASSWORD, user.getPassword());
db.insert(TABLE_USERS, null, values);
db.close();
}
public User getUser(String Email){
SQLiteDatabase db=this.getReadableDatabase();
Cursor cursor=
db.query(TABLE_USERS, COLUMNS, "Email =?", new String[] {String.valueOf(Email)}, null, null, null);
if (cursor != null)
cursor.moveToFirst();
User user=new User();
user.setFirstName(cursor.getString(0));
user.setLastName(cursor.getString(1));
user.setEmail(cursor.getString(2));
user.setUsername(cursor.getString(3));
user.setPassword(cursor.getString(4));
Log.d("getUser ("+Email+")", user.toString());
return user;
}
public List<User> getAllUsers(){
List<User> users=new LinkedList<User>();
String query="SELECT * FROM "+TABLE_USERS;
SQLiteDatabase db=this.getWritableDatabase();
Cursor cursor= db.rawQuery(query, null);
User user=null;
if (cursor.moveToFirst()){
do{
user=new User();
user.setFirstName(cursor.getString(0));
user.setLastName(cursor.getString(1));
user.setEmail(cursor.getString(2));
user.setUsername(cursor.getString(3));
user.setPassword(cursor.getString(4));
users.add(user);
} while (cursor.moveToNext());
}
Log.d("getAllUsers", users.toString());
return users;
}
public int updateUser(User user){
SQLiteDatabase db=this.getWritableDatabase();
ContentValues values=new ContentValues();
values.put(FIRST_NAME, user.getFirstName());
values.put(LAST_NAME, user.getLastName());
values.put(EMAIL, user.getEmail());
values.put(USERNAME, user.getUsername());
values.put(PASSWORD, user.getPassword());
int i=db.update(TABLE_USERS, values, "Email =?", new String[]{String.valueOf(user.getEmail())});
db.close();
return i;
}
public void deleteUser(User user){
SQLiteDatabase db=this.getWritableDatabase();
db.delete(TABLE_USERS, "Email =?", new String[]{String.valueOf(user.getEmail())});
db.close();
Log.d("deleteUser", user.toString());
}
}
LogCat:
日志猫：
04-18 12:16:09.132: E/Trace(1051): error opening trace file: No such file or directory (2)
04-18 12:16:09.404: D/libEGL(1051): loaded /system/lib/egl/libEGL_emulation.so
04-18 12:16:09.416: D/(1051): HostConnection::get() New Host Connection established 0xb9324060, tid 1051
04-18 12:16:09.492: D/libEGL(1051): loaded /system/lib/egl/libGLESv1_CM_emulation.so
04-18 12:16:09.492: D/libEGL(1051): loaded /system/lib/egl/libGLESv2_emulation.so
04-18 12:16:09.672: W/EGL_emulation(1051): eglSurfaceAttrib not implemented
04-18 12:16:09.708: D/OpenGLRenderer(1051): Enabling debug mode 0
04-18 12:16:09.800: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb931a8e0): name, size, mSize = 1, 1048576, 1048576
04-18 12:16:09.960: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb9331d10): name, size, mSize = 2, 5184, 1053760
04-18 12:16:10.068: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb9309b60): name, size, mSize = 4, 20736, 1074496
04-18 12:16:10.072: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb932d4b8): name, size, mSize = 5, 9216, 1083712
04-18 12:16:10.140: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb9312810): name, size, mSize = 7, 7488, 1091200
04-18 12:16:10.152: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb9325d70): name, size, mSize = 8, 100, 1091300
04-18 12:16:10.212: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb93176a0): name, size, mSize = 10, 7488, 1098788
04-18 12:16:10.252: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb9373798): name, size, mSize = 11, 7488, 1106276
04-18 12:16:10.336: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb9315840): name, size, mSize = 12, 2304, 1108580
04-18 12:16:42.528: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb9378b38): name, size, mSize = 78, 7488, 1116068
04-18 12:16:42.800: D/dalvikvm(1051): GC_CONCURRENT freed 142K, 3% free 8216K/8391K, paused 14ms+0ms, total 25ms
04-18 12:16:44.200: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb9308998): name, size, mSize = 85, 7488, 1123556
04-18 12:16:44.216: D/OpenGLRenderer(1051): TextureCache::get: create texture(0xb9316848): name, size, mSize = 86, 7488, 1131044
04-18 12:16:53.192: D/addUser(1051): First name: dsfLast name: dsfdsfEmail: dsfdsfUsername: Password:
04-18 12:16:53.196: D/AndroidRuntime(1051): Shutting down VM
04-18 12:16:53.196: W/dalvikvm(1051): threadid=1: thread exiting with uncaught exception (group=0xa627b288)
04-18 12:16:53.200: E/AndroidRuntime(1051): FATAL EXCEPTION: main
04-18 12:16:53.200: E/AndroidRuntime(1051): java.lang.NullPointerException
04-18 12:16:53.200: E/AndroidRuntime(1051): at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
04-18 12:16:53.200: E/AndroidRuntime(1051): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
04-18 12:16:53.200: E/AndroidRuntime(1051): at com.craftyonhand.www.MySQLiteOpenHelper.addUser(MySQLiteOpenHelper.java:60)
04-18 12:16:53.200: E/AndroidRuntime(1051): at com.craftyonhand.www.registration.onClick(registration.java:47)
04-18 12:16:53.200: E/AndroidRuntime(1051): at android.view.View.performClick(View.java:4084)
04-18 12:16:53.200: E/AndroidRuntime(1051): at android.view.View$PerformClick.run(View.java:16966)
04-18 12:16:53.200: E/AndroidRuntime(1051): at android.os.Handler.handleCallback(Handler.java:615)
04-18 12:16:53.200: E/AndroidRuntime(1051): at android.os.Handler.dispatchMessage(Handler.java:92)
04-18 12:16:53.200: E/AndroidRuntime(1051): at android.os.Looper.loop(Looper.java:137)
04-18 12:16:53.200: E/AndroidRuntime(1051): at android.app.ActivityThread.main(ActivityThread.java:4745)
04-18 12:16:53.200: E/AndroidRuntime(1051): at java.lang.reflect.Method.invokeNative(Native Method)
04-18 12:16:53.200: E/AndroidRuntime(1051): at java.lang.reflect.Method.invoke(Method.java:511)
04-18 12:16:53.200: E/AndroidRuntime(1051): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-18 12:16:53.200: E/AndroidRuntime(1051): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-18 12:16:53.200: E/AndroidRuntime(1051): at dalvik.system.NativeStart.main(Native Method)
04-18 12:16:55.792: I/Process(1051): Sending signal. PID: 1051 SIG: 9
回答by laalto
MySQLiteOpenHelper db = new MySQLiteOpenHelper(null);//do I need this??
Yes you need it and you also need to pass a non-nullvalid Contextas an argument. In a fragment, you can use getActivity()to get the activity to use as a Contextonce the fragment is attached to its host activity.
是的，您需要它，并且您还需要传递一个null无效Context的参数。在片段中，一旦片段附加到其宿主活动，您就可以使用getActivity()获取活动以用作Context。
Okay so it does show on logcat but for some reason it says that there is no such table USERS... As far as I know it should open it if it does not exsits. Am I wrong?
好的，它确实显示在 logcat 上，但出于某种原因，它说没有这样的表 USERS...据我所知，如果它不存在，它应该打开它。我错了吗？
Possibly you have an older version of the database file around. Clear app data or uninstall it to remove it and make the database helper onCreate()create set up the tables for you. See When is SQLiteOpenHelper onCreate() / onUpgrade() run?for more.
可能你有一个旧版本的数据库文件。清除应用程序数据或卸载它以将其删除并让数据库助手onCreate()为您创建设置表。请参阅SQLiteOpenHelper onCreate() / onUpgrade() 何时运行？更多。
回答by M D
You should change this
你应该改变这个
MySQLiteOpenHelper db = new MySQLiteOpenHelper(null);//do I need this??
With
和
MySQLiteOpenHelper db = new MySQLiteOpenHelper(getActivity());//do I need this??
回答by Biraj Zalavadia
Replace
代替
MySQLiteOpenHelper db = new MySQLiteOpenHelper(null);
with
和
MySQLiteOpenHelper db = new MySQLiteOpenHelper(getActivity());
Update onUpgrade()method
更新onUpgrade()方式
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
String CREATE_MyDB_TABLE = "CREATE TABLE IF NOT EXISTS USERS ( " +
"First_name TEXT, " +
"Last_name TEXT, "+
"Email KEY TEXT NOT NULL, "+
"Username TEXT NOT NULL, "+
"Password TEXT NOT NULL)";
db.execSQL(CREATE_MyDB_TABLE);
this.onCreate(db);
}
