java - 在 sqlite 数据库中插入信息不起作用

Question

已经存储在数据库中的文本显示没有任何问题。但是新插入的数据没有显示。我认为“添加新文本不会显示任何内容，就好像没有执行插入操作一样。”。我不知道为什么它不起作用。请帮助...

我的 DatabaseHandler 类

 public class databaseHandler extends SQLiteOpenHelper
{

    private Context main_context;
    private static String DB_PATH;
    private static String DB_NAME = "word.sqlite";
    private static String DB_TBL_BOOKS = "word";
    private static String DB_TBL_SETTING = "setting";
    private static final  int DB_version = 1;
    public static final String COLUMN_ID = "ID";
    public static final String COLUMN_FIRST_NAME = "title";
    public static final String COLUMN_LAST_NAME = "content";
    private SQLiteDatabase db;

    public databaseHandler(Context con)
    {



        super(con, DB_NAME, null, DB_version);

        main_context = con;
        DB_PATH = con.getCacheDir().getPath() + "/" +DB_NAME;

    }
    public void createDataBase() throws IOException {
        boolean dbExist = checkDataBase();
        if (dbExist) {
            // do nothing - database already exist
        } else {

            // By calling this method and 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();
            copyDB();
        }
    }

    /**
     * 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 does't exist yet.
        }
        if (checkDB != null) {
            checkDB.close();
        }
        return checkDB != null ? true : false;
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        String query;
        query = "CREATE TABLE word (id INTEGER PRIMARY KEY  NOT NULL , title VARCHAR, content VARCHAR DEFAULT null)";
        db.execSQL(query);
        Log.d("log","table Created");


    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
    {
        Log.w("tag", "Upgrading database from version " + oldVersion + " to "
                + newVersion + ", which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS word");
        onCreate(db);
    }

    private boolean db_exist() {

        File f = new File(DB_PATH);
        if (f.exists())
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    private boolean copyDB() {
        try {
            FileOutputStream out = new FileOutputStream(DB_PATH);
            InputStream in =main_context.getAssets().open(DB_NAME);
            byte[] buffer = new byte[1024];
            int ch;
            while ((ch = in.read(buffer)) > 0)
            {
                out.write(buffer , 0, ch);
            }
            out.flush();
            out.close();
            in.close();
            return true;
        } catch (Exception e) {
            Log.i("amirmessage", "error in 84 -> " + e.toString());
            return false;
        }
    }



    public void open()
    {
        if (db_exist())
        {
            try {
                File temp = new File(DB_PATH);
                db =SQLiteDatabase.openDatabase(temp.getAbsolutePath() , null ,  SQLiteDatabase.OPEN_READWRITE);
            }catch (Exception e) {
                Log.i("amirmessage", "error in 100 -> " + e.toString());

            }

        }
        else {
            if (copyDB())
            {
                open();
            }

        }
    }
    @Override
    public synchronized void close() {

        db.close();
    }
    //---------




    public List<HashMap<String , Object>> getresultOfSerach()
    {
        Cursor result = db.rawQuery("SELECT * FROM "+ DB_TBL_BOOKS  ,null);
        List<HashMap<String , Object>> all_data = new ArrayList<>();

       try {
           while ( result.moveToNext())
           {
               HashMap<String , Object> temp = new HashMap<>();
               temp.put("id" , result.getString(0));
               temp.put("content" , result.getString(2));


               temp.put("title" , result.getString(1));



               all_data.add(temp);
               Log.d("update","Query: ");

           }
       } finally
        {
            result.close();
        }



        return all_data;
    }


    public void addcontent(String state, String title)
    {

        ContentValues cv  = new ContentValues();
        cv.put("content", state);
        cv.put("title", title);
        db = this.getWritableDatabase();


            db.insert(DB_TBL_BOOKS,null,cv);

        Toast.makeText(main_context,state+title , Toast.LENGTH_SHORT).show();

    }
 }

我的 Activity 插入代码在这里

public class addcontent extends AppCompatActivity 

  {

    private databaseHandler db;
    public String title1;
    public String content;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_addcontent);
        db = new databaseHandler(getBaseContext());
        sharedpreferences = getSharedPreferences(MyPREFERENCES, Context.MODE_PRIVATE);

        EditText etcontent = (EditText)findViewById(R.id.editText);
        EditText ettitle1 = (EditText)findViewById(R.id.editText2);

        title1=ettitle1.getText().toString();
        content=etcontent.getText().toString();


    }

      public void onbtnadd(View v)
    {

        db.open();
        db.addcontent( content,title1);

        db.close();

    }
}

我显示信息的 MainActivity 代码在这里

 public class Main2Activity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

private databaseHandler db;
private ListView resultListView;
private List<HashMap<String , Object>> resultsbooks;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Intent i = new Intent(getBaseContext(),addcontent.class);
            startActivity(i);
        }
    });

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    resultListView = (ListView) findViewById(R.id.catListview);
    db = new databaseHandler(getBaseContext());
    showresultOfSerarch();
}

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main2, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();

    if (id == R.id.nav_camera) {
        // Handle the camera action
    } else if (id == R.id.nav_gallery) {

    } else if (id == R.id.nav_slideshow) {

    } else if (id == R.id.nav_manage) {

    } else if (id == R.id.nav_share) {

    } else if (id == R.id.nav_send) {

    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

public void onbtnfind()
{
    resultListView.setAdapter(null);

    String serachBy;

    serachBy = "author";


    String query =" ";


    showresultOfSerarch();

}
  public void showresultOfSerarch() 
{
    db.open();

    resultsbooks = db.getresultOfSerach();
    db.close();


    String[] from = {"title","content"};
    int[] to = {R.id.txttitle,  R.id.txtcontent};

    SimpleAdapter adp = new SimpleAdapter(
            getBaseContext(), resultsbooks, R.layout.tbl_contest_row, from, to
    );
    resultListView.setAdapter(adp);
 }

Answer 1

首先我想说的是，请遵循编码指南。

您没有准备显示插入“word”表中的数据。

您的数据插入逻辑工作正常。一旦您的数据被添加到“word”表中，请尝试读取值。您可以对读取值进行以下更改。

public void onbtnadd() {
    db.open();
    db.addcontent(content, title1);
    Cursor cursor = db.getReadableDatabase().rawQuery("select * from word", null);
    if (cursor.moveToFirst()) {
        do {
            // get all records inserted in 'word' table here
        } while (cursor.moveToNext());
    }
    db.close();
}