当我返回上一个活动时，内容不会出现

Question

我有一个关于写笔记的Android应用程序。当我按 Second2 活动中的编辑按钮时，它将移动到 Second3 活动而没有任何问题（在 Second3 活动我可以编辑该注释而不用任何问题）。但是当我按下“保存”按钮时，它将返回 Second2 ，但没有任何内容出现！它只是一个空的活动！请帮帮我！

MainActivity类：

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;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;

public class MainActivity extends ActionBarActivity implements AdapterView.OnItemClickListener {

    ListView lv;
    NotesDataSource nDS;
    List<NotesModel> notesList;
    String[] notes;
    int i;
    ArrayAdapter<String> adapter;
    AdView mAdView;
    AdRequest adRequest;
    public static long back_pressed;

    @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();

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

        for (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);

        mAdView = (AdView) findViewById(R.id.adView);
        adRequest = new AdRequest.Builder().build();
        mAdView.loadAd(adRequest);
    }

    @Override
    public void onBackPressed()
    {
        if (back_pressed + 2000 > System.currentTimeMillis()) super.onBackPressed();
        else Toast.makeText(this, "Press once again to exit!", Toast.LENGTH_SHORT).show();
        back_pressed = System.currentTimeMillis();
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        Intent nView = new Intent(this, Second2.class);
        nView.putExtra("id", notesList.get(position).getId());
        nView.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        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:
                AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
                nDS.open();
                nDS.deleteNote(notesList.get(info.position).getId());
                notesList = nDS.getAllNotes();
                nDS.close();

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

                for (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);

                Toast nDelete = Toast.makeText(this, R.string.deleted, Toast.LENGTH_LONG);
                nDelete.show();
        }
        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(getString(R.string.about_title));
                aboutDialog.setMessage(R.string.about_body);
                aboutDialog.setIcon(R.drawable.my_notes);
                aboutDialog.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface aboutDialog, int witch) {
                        // Do Not Do Anything.
                    }
                });

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

第二课：

package com.twitter.i_droidi.mynotes;

import android.content.Intent;
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;

    @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.createNote(noteTitle.getText().toString(), noteBody.getText().toString());
                    nDS.close();
                    Toast nSave = Toast.makeText(this, R.string.saved, Toast.LENGTH_LONG);
                    nSave.show();
                    Intent nView = new Intent(this, MainActivity.class);
                    nView.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                    startActivity(nView);
                } else {
                    Toast notSave = Toast.makeText(this, R.string.do_not_save, Toast.LENGTH_LONG);
                    notSave.show();
                }
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

第二课：

package com.twitter.i_droidi.mynotes;

import android.content.Intent;
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.TextView;

public class Second2 extends ActionBarActivity {

    TextView viewNoteTitle;
    TextView viewNoteBody;
    int id;
    NotesDataSource nDS;
    NotesModel note;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second2);

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

        viewNoteTitle = (TextView) findViewById(R.id.view_note_title);
        viewNoteBody = (TextView) findViewById(R.id.view_note);
        nDS = new NotesDataSource(this);

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

        viewNoteTitle.setText(note.getTitle());
        viewNoteBody.setText(note.getBody());
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_second2, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.second2MenuEdit:
                Intent nEdit = new Intent(this, Second3.class);
                nEdit.putExtra("id", note.getId());
                nEdit.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(nEdit);
        }
        return super.onOptionsItemSelected(item);
    }
}

第二课：

package com.twitter.i_droidi.mynotes;

import android.content.Intent;
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 Second3 extends ActionBarActivity {

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

    @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, R.string.saved, Toast.LENGTH_LONG);
                    nSave.show();
                    Intent nView = new Intent(this, Second2.class);
                    nView.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                    startActivity(nView);
                } else {
                    Toast notSave = Toast.makeText(this, R.string.do_not_save, Toast.LENGTH_LONG);
                    notSave.show();
                }
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

Answer 1

第二个活动从这两行获取来自Intent的数据：

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

因此，当您从第三个活动返回此活动时，您将笔记保存在以下行中：

Intent nView = new Intent(this, Second2.class);
nView.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(nView);

您必须像在Main Activity类中那样将ID添加到Intent中，您可以按照以下方式执行此操作，但是您在第三个活动中没有noteList数组。

nView.putExtra("id", notesList.get(position).getId());

因此，获取活动数据的最简单方法是调用

finish();

这是因为第二个活动仍然在活动堆栈中而你不必再次启动它，你可以完成第三个活动而第二个活动就会显示，因为它是堆栈中的最后一个活动。但标题不会更新，因此您必须从下面的代码开始启动Activity：

保存完笔记后。

@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, R.string.saved, Toast.LENGTH_LONG);
                    nSave.show();
                    Intent nView = new Intent(this, Second2.class);
                    nView.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                    nView.putExtra("id", id);

                    startActivity(nView);
                    finish();
                } else {
                    Toast notSave = Toast.makeText(this, R.string.do_not_save, Toast.LENGTH_LONG);
                    notSave.show();
                }
                return true;
    }
    return super.onOptionsItemSelected(item);
}

对于你希望最后的问题，在第二个活动中覆盖onBackPressed方法并添加以下代码：

 @Override
    public void onBackPressed()
    {
        Intent intent = new Intent(this, MainActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(intent);
        finish();
    }