java - 从 fragment 访问 SQLite 数据库

标签 java android sqlite android-fragments sqliteopenhelper

我的应用程序包含 MainActivity 类和几个 fragment 。 其中之一是注册 fragment ，我希望它能够与我的数据库交互，该数据库应该只包含一个名为 USERS 的表，我将对其进行 CRUD。 我打开了扩展 SQLiteOpenHelper 的 MySQLiteOpenHelper 类，并创建了一个 User 类。 我已经声明:

MySQLiteOpenHelper db = new MySQLiteOpenHelper(this);

在 Activity 的 onCreate 方法中。 我的问题是如何从 fragment 中与这个数据库交互？ 我已经尝试了以下代码，但没有成功:

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()));
        }
    });

}
}

现在发生的事情是，当我点击“完成”按钮时，应用程序崩溃了…… 谢谢!!

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());
    }

}

日志:

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$1.onClick(registration.java:47)
    04-18 12:16:53.200: E/AndroidRuntime(1051):     at android.view.View.performClick(View.java:4084)
    04-18 12:16:53.200: E/AndroidRuntime(1051):     at android.view.View$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

最佳答案 

MySQLiteOpenHelper db = new MySQLiteOpenHelper(null);//do I need this??

是的，你需要它，你还需要传递一个非 null 有效的 Context 作为参数。在 fragment 中，您可以使用 getActivity() 获取 Activity 以用作 Context，一旦 fragment 附加到其宿主 Activity 。

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?

可能您周围有旧版本的数据库文件。清除应用程序数据或将其卸载以将其删除并让数据库助手 onCreate() 为您创 build 置表。参见 When is SQLiteOpenHelper onCreate() / onUpgrade() run? 了解更多。

关于java - 从 fragment 访问 SQLite 数据库，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/23154037/

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