Question

在我的Android应用中保存注释后，注释的注释（或ListView）不会出现在 MainActivity 中。我的应用的 MainActivity类是：

package com.twitter.i_droidi.mynotes;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import java.util.List;

public class MainActivity extends ActionBarActivity implements AdapterView.OnItemClickListener {

    ListView lv;
    NotesDataSource nDS;
    List<NotesModel> notesList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        nDS = new NotesDataSource(this);
        lv = (ListView) findViewById(R.id.lv);

        nDS.open();
        notesList = nDS.getAllNotes();
        nDS.close();

        String[] notes = new String[notesList.size()];

        for (int i = 0; i < notesList.size(); i++) {
            notes[i] = notesList.get(i).getTitle();
        }

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1,
                android.R.id.text1, notes);
        lv.setAdapter(adapter);

        registerForContextMenu(lv);
        lv.setOnItemClickListener(this);
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        Intent nView = new Intent(this, Second.class);
        nView.putExtra("id", notesList.get(position).getId()); // Check...!!!
        startActivity(nView);
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_delete, menu);
        super.onCreateContextMenu(menu, v, menuInfo);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.delete:
                nDS.open();
                nDS.deleteNote(lv.getId()); // Check...!!!
                nDS.close();
                Toast nDelete = Toast.makeText(this, "Deleted.", Toast.LENGTH_LONG);
                nDelete.show();
                return true;
        }
        return super.onContextItemSelected(item);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.mainMenuNewNote:
                Intent nNote = new Intent(this, Second.class);
                startActivity(nNote);
                return true;

            case R.id.mainMenuAbout:
                AlertDialog.Builder aboutDialog = new AlertDialog.Builder(this);
                aboutDialog.setTitle("About the app");
                aboutDialog.setMessage("The Simplest app for notes!\n\n" +
                        "Developed by: Abdulaziz\n" +
                        "Twitter: @i_Droidi\n" +
                        "Telegram: MrGlitch\n\n" +
                        "Special Thanks to who tested the app before upload it on Play Store and to who use it now! :)");
                aboutDialog.setIcon(R.mipmap.ic_launcher);
                aboutDialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface aboutDialog, int witch) {
                        // Do Not Do Anything.
                    }
                });

                aboutDialog.show();
                return true;

            case R.id.mainMenuExit:
                AlertDialog.Builder exDialog = new AlertDialog.Builder(this);
                exDialog.setTitle("Exit?");
                exDialog.setMessage("Are you sure to exit?");
                exDialog.setIcon(R.mipmap.ic_launcher);
                exDialog.setNegativeButton("Yes", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface exDialog, int which) {
                        finish();
                    }
                });
                exDialog.setPositiveButton("No", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface exDialog, int which) {
                        // Do Not Do Anything.
                    }
                });

                exDialog.show();
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

我的应用的 activity_main （xml /布局文件）是：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <ListView
        android:id="@+id/lv"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"></ListView>

</LinearLayout>

我的应用的第二课是：

package com.twitter.i_droidi.mynotes;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.Toast;

public class Second extends ActionBarActivity {

    NotesDataSource nDS;
    EditText noteTitle;
    EditText noteBody;
    int id;
    DB db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second);

        Intent in = getIntent();
        id = in.getIntExtra("id", 0);

        noteTitle = (EditText) findViewById(R.id.note_title);
        noteBody = (EditText) findViewById(R.id.note);
        nDS = new NotesDataSource(this);

        nDS.open();
        NotesModel note = nDS.getNote(id);
        nDS.close();

        noteTitle.setText(note.getTitle());
        noteBody.setText(note.getBody());
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_second, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.secondMenuSave:
                if (!noteTitle.getText().toString().isEmpty() && !noteBody.getText().toString().isEmpty()) {
                    nDS.open();
                    nDS.updateNote(id, noteTitle.getText().toString(), noteBody.getText().toString());
                    nDS.close();
                    Toast nSave = Toast.makeText(this, "Saved.", Toast.LENGTH_LONG);
                    nSave.show();
                    finish();
                } else {
                    Toast notSave = Toast.makeText(this, "The title and content of the note CANNOT be empty!", Toast.LENGTH_LONG);
                    notSave.show();
                }
                return true;

            case R.id.secondMenuBack:
                AlertDialog.Builder baDialog = new AlertDialog.Builder(this);
                baDialog.setTitle("Back?");
                baDialog.setMessage("Do you want to back to the main page before saving the note?");
                baDialog.setIcon(R.mipmap.ic_launcher);
                baDialog.setNegativeButton("Yes", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface baDialog, int which) {
                        finish();
                    }
                });
                baDialog.setPositiveButton("No", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface baDialog, int which) {
                        // Do Not Do Anything.
                    }
                });

                baDialog.show();
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

我的应用的 NotesDataSource类是：

package com.twitter.i_droidi.mynotes;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import java.util.ArrayList;
import java.util.List;

public class NotesDataSource {

    DB myDB;
    SQLiteDatabase sql;

    String[] getAllColumns = new String[]{DB.ID, DB.TITLE, DB.BODY};

    public NotesDataSource(Context context) {
        myDB = new DB(context);
    }

    public void open() {
        try {
            sql = myDB.getWritableDatabase();
        } catch (Exception ex) {
            Log.d("Error in your database!", ex.getMessage());
        }
    }

    public void close() {
        sql.close();
    }

    public void createNote(String title, String body) {
        ContentValues note = new ContentValues();
        note.put(myDB.TITLE, title);
        note.put(myDB.BODY, body);
        sql.insert(myDB.TABLE_NAME, null, note);
    }

    public NotesModel getNote(int id) {
        NotesModel note = new NotesModel();

        Cursor cursor = sql.rawQuery("SELECT * FROM " + DB.TABLE_NAME + " WHERE " + DB.ID + " = ?", new String[]{id + ""});

        if (cursor.getCount() > 0) {
            cursor.moveToFirst();
            note.setId(cursor.getInt(0));
            note.setTitle(cursor.getString(1));
            note.setBody(cursor.getString(2));
            cursor.close();
        }
        return note;
    }

    public void updateNote(int id, String title, String body) {
        ContentValues note = new ContentValues();
        note.put(myDB.TITLE, title);
        note.put(myDB.BODY, body);
        sql.update(myDB.TABLE_NAME, note, myDB.ID + " = " + id, null);
    }

    public void deleteNote(Object id) {
        sql.delete(myDB.TABLE_NAME, myDB.ID + " = " + id, null);
    }

    public List<NotesModel> getAllNotes() {
        List<NotesModel> notesList = new ArrayList<NotesModel>();

        Cursor cursor = sql.query(myDB.TABLE_NAME, getAllColumns, null, null, null, null, null);
        cursor.moveToFirst();

        while (!cursor.isAfterLast()) {
            NotesModel notes = new NotesModel();
            notes.setId(cursor.getInt(0));
            notes.setTitle(cursor.getString(1));
            notes.setBody(cursor.getString(2));

            notesList.add(notes);
            cursor.moveToNext();
        }

        cursor.close();
        return notesList;
    }
}

我的应用的数据库类是：

package com.twitter.i_droidi.mynotes;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DB extends SQLiteOpenHelper {

    private static final String DB_NAME = "MyNotes";
    private static final int DB_VERSION = 1;

    public static final String TABLE_NAME = "MyNotes";
    public static final String ID = "id";
    public static final String TITLE = "title";
    public static final String BODY = "body";

    private static final String DB_CREATE = "create table " + TABLE_NAME + " (" + ID + " integer primary key autoincrement, " +
            TITLE + " text not null, " + BODY + " text not null)";

    public DB(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(DB_CREATE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }
}

我的应用（MainActivity）的屏幕截图，保存注释后（Nothing shows！）：

A screenshot of my app, after saving the note (Nothing shows!)

我如何解决这个问题？！

或者任何人都可以写出正确的代码？！

感谢您的帮助。

Answer 1

问题是onCreate仅在生命周期中被调用一次。切换活动时，只需隐藏和暂停Main。当您返回活动时，onCreate不会再次触发。

重写onStart方法并在其中设置列表适配器。当您返回到视图时，它将在onCreate（）和之后立即调用。这是Android生命周期：

http://developer.android.com/training/basics/activity-lifecycle/starting.html

Answer 2

此答案假设您的Second活动的实施为某些全局模型添加了新注释，并且此模型的状态反映在您{＆n}的nDS对象中{39}已在<{1}}中创建已 {MainActivity onCreate() MainActivity finish() Second ListView MainActivity 。

你绝对应该测试上述假设是否正确。如果不是，您可以使用某种形式的Singleton设计模式来存储数据。

为了将更改反映到public class MainActivity extends ActionBarActivity implements AdapterView.OnItemClickListener { ArrayAdapter<String> adapter; NotesDataSource nDS; List < NotesModel > notesList; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); nDS = new NotesDataSource(this); ListView lv = (ListView) findViewById(R.id.lv); nDS.open(); notesList = nDS.getAllNotes(); nDS.close(); String[] notes = new String[notesList.size()]; for (int i = 0; i < notesList.size(); i++) { notes[i] = notesList.get(i).getTitle(); } adapter = new ArrayAdapter < String > (MainActivity.this, android.R.layout.simple_list_item_1, android.R.id.text1, notes); lv.setAdapter(adapter); registerForContextMenu(lv); lv.setOnItemClickListener(this); } @Override protected void onResume() { super.onResume(); nDS.open(); notesList = nDS.getAllNotes(); nDS.close(); String[] notes = new String[notesList.size()]; for (int i = 0; i < notesList.size(); i++) { notes[i] = notesList.get(i).getTitle(); } adapter.clear(); adapter.addAll(notes); adapter.notifyDataSetChanged(); } // No changes in other methods ...修改/在ArrayAdapter<String>中添加以下代码：

List<NotesModel>

}

附加说明：维护ListAdapter和class CustomAdapter extends ArrayAdapter<NotesModel> { ... }非常低效且容易出错。如果您实现自定义$idArray= DB::table('A')->select(DB::Raw('id, MAX(date)'))->groupBy('id')->lists('id'); $query = DB::table('B')->whereIn('id', $idArray)->get();会更好。你可以使用这样的东西：

( ! ) Warning: require_once(C:\wamp\www\job\web/../app/bootstrap.php.cache): failed to open stream: No such file or directory in C:\wamp\www\job\web\app_dev.php on line 22

可以找到有关编写自定义适配器的优秀教程here。

Answer 3

我认为您的代码中存在两个问题

1）首先替换

public List<NotesModel> getAllNotes() {
        List<NotesModel> notesList = new ArrayList<NotesModel>();

        Cursor cursor = sql.query(myDB.TABLE_NAME, getAllColumns, null, null, null, null, null);
        cursor.moveToFirst();

        while (!cursor.isAfterLast()) {
            NotesModel notes = new NotesModel();
            notes.setId(cursor.getInt(0));
            notes.setTitle(cursor.getString(1));
            notes.setBody(cursor.getString(2));

            notesList.add(notes);
            cursor.moveToNext();
        }

        cursor.close();
        return notesList;
    }

与这些

public List<NotesModel> getAllNotes() {
        List<NotesModel> notesList = new ArrayList<NotesModel>();

StringBuffer selectQuery = new StringBuffer();
selectQuery.append("SELECT * FROM "+myDB.TABLE_NAME+"");

        Cursor cursor = sql.rawQuery(selectQuery.toString(),null);

if (cursor != null && cursor.moveToFirst()) {
            do {
               NotesModel notes = new NotesModel();
            notes.setId(cursor.getInt(0));
            notes.setTitle(cursor.getString(1));
            notes.setBody(cursor.getString(2));

            notesList.add(notes);

            } while (cursor.moveToNext());
        }


        cursor.close();
        return notesList;
    }

2）转到列表项目的第二课，点击这样 -

Intent nView = new Intent(this, Second.class);
        nView.putExtra("id", notesList.get(position).getId()); // Check...!!!
nView.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(nView);

并在添加注释后返回MainActivity，就像这样----

Intent nView = new Intent(this, MainActivity.class);
        nView.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(nView);

不要使用完成，因为它只会结束当前任务并在不刷新的情况下取出堆叠中的上一个屏幕

ListView没有出现在我的应用程序的MainActivty中（附带图像）

3 个答案: