使用 SwipeDismissListViewTouchListener 删除项目后使用 Android 后退按钮答案

【问题标题】：Using Android back button after delete an item with SwipeDismissListViewTouchListener使用 SwipeDismissListViewTouchListener 删除项目后使用 Android 后退按钮
【发布时间】：2017-09-20 05:26:44
【问题描述】：

在我的应用 (API 17) 中使用后退按钮时遇到问题。我的项目中有两个活动： ListView 从 xml 文件中读取项目的主要活动。

第二个活动正在读取相同的 xml 文件，但仅使用已由主要活动检查并保存的项目。

如果我在第二个活动中从 ListView 中删除一个项目，并在滑动时保存 xml 文件后使用应用程序的菜单返回到主活动，则该项目现在未选中。这是因为 xml 文件在刷卡后已更改，并且“isDone”的值从 true 设置为 false。

到目前为止一切顺利！

但如果我使用 Android 后退按钮返回，已删除的项目仍处于选中状态。
什么地方出了错？我想这与活动的生命周期有关。但我想不通。我是否必须再次阅读 onResume 中更改和保存的 xml 文件？我假设在使用第二个活动的后退按钮后主活动开始时会再次读取它。

而我真正不明白的是：当我调试代码时，我可以看到在第二个活动中滑动项目并将更改后的 isDone 值保存到 xml 后，xml 文件没有被更改。这对我来说似乎有点奇怪。

任何帮助都可以！

主要活动：

    package com.wbapps.wbshoppinglist;

/**
 * Created by Andreas on 9/4/2017.
 */

import android.support.v7.app.ActionBar;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.ContextMenu;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import org.xmlpull.v1.XmlPullParserException;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

public class MainActivity extends AppCompatActivity {
    /*wb, 19Sep,2017: not yet
    public static final int REQUEST_ID = 1;
     */
    ImageButton imgbtnAddItem;
    Button btn_create_shopping_list;
    EditText input;

    //object for the ListView from activity_main.xml
    ListView list_view;

    List<Task> tasks;
    TodoListAdapter adapter;
    XmlParser parser;
    File file;
    ActionBar actionBar;

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

        file = new File(Environment.getExternalStorageDirectory(), "tasks.xml");
        parser = new XmlParser();
        tasks = new ArrayList<Task>();

        //file.delete();
        if (file.exists()) {
            try {
                tasks = parser.read(file);
                if (tasks.isEmpty()) {
                    file.delete();
                    file.createNewFile();
                }else {sortList();}
            } catch (XmlPullParserException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            } catch (FileNotFoundException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            } catch (IOException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            }
        } else {
            try {
                file.createNewFile();
            } catch (IOException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            }
        }

        //Initialize the variables
        imgbtnAddItem = (ImageButton) findViewById(R.id.add_task_button);
        btn_create_shopping_list = (Button) findViewById(R.id.create_shopping_list);
        /* findViewById(R.id.list_view).requestFocus(); */
        input = (EditText) findViewById(R.id.input_task);
        /* id list_view identifies the listview from the activity_main.xmll */
        list_view = (ListView) findViewById(R.id.list_view);
        registerForContextMenu(list_view);

        //tasks = new ArrayList<Task>();
        adapter = new TodoListAdapter(tasks, this);
        list_view.setAdapter(adapter);

        //To swipe away an litem from the list
        SwipeDismissListViewTouchListener touchListener =
                new SwipeDismissListViewTouchListener(
                        list_view,
                        new SwipeDismissListViewTouchListener.DismissCallbacks() {
                            @Override
                            public boolean canDismiss(int position) {
                                return true;
                            }

                            @Override
                            public void onDismiss(ListView listView, int[] reverseSortedPositions) {
                                for (int position : reverseSortedPositions) {
                                    tasks.remove(position);
                                    adapter.notifyDataSetChanged();
                                }
                            }
                        });
        list_view.setOnTouchListener(touchListener);

        //set the onClickListener for the button
        imgbtnAddItem.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                if (input.getText().length() > 0) {
                    /* wb, 16Sep2017: look if the new item is already in the list */
                    Boolean itemfound = false;
                    for (int i = 0; i<tasks.size(); i++){
                        if (tasks.get(i).getTaskContent().equalsIgnoreCase(input.getText().toString())){
                            itemfound = true;
                            AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                            builder.setMessage("This item is already in the list!");
                            AlertDialog dialog = builder.create();
                            dialog.show();
                            break;
                        }
                    }

                    if (itemfound == false){
                        tasks.add(new Task(input.getText().toString(), false));
                        adapter.notifyDataSetChanged();
                        sortList();
                        input.setText("");
                    }

                }
            }
        });

        btn_create_shopping_list.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                //startActivity(new Intent(MainActivity.this, ShoppingListActivity.class));
                Boolean selected = false;
                Task taskTmp;
                for (int i = 0; i < tasks.size(); i++) {
                    taskTmp = tasks.get(i);
                    if (taskTmp.isDone()) {
                        selected = true;
                        break;
                    }
                }

                if (selected) {
                    Intent intent = new Intent(getApplicationContext(), ShoppingListActivity.class);
                    startActivity(intent);
                    /* startActivityForResult(intent, REQUEST_ID); */
                } else {
                    AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                    builder.setMessage("No items for shopping list selected!");
                    AlertDialog dialog = builder.create();
                    dialog.show();
                }
            }
        });

    }

    @Override
    protected void onPause() {
        super.onPause();
        //wb, Sep 13, 2017:
        //before doing something else - like calling a new activity - write the altered list to
        //the data sourc file tasks.xml file
        try {
            parser.write(tasks, file);
        } catch (IOException ex) {
            Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        /* Do I have to do the same here like in onCreate? It does not work yet!*/
        if (file.exists()) {
            try {
                tasks = parser.read(file);
                if (tasks.isEmpty()) {
                    file.delete();
                    file.createNewFile();
                }else {sortList();}
            } catch (XmlPullParserException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            } catch (FileNotFoundException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            } catch (IOException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            }
        } else {
            try {
                file.createNewFile();
            } catch (IOException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
    }

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_clear_all:
                clearDonetasks();
                this.adapter.notifyDataSetChanged();
                break;
            case R.id.action_delete_done_tasks:
                deleteDonetasks();
                this.adapter.notifyDataSetChanged();
                break;
            case R.id.action_delete_all:
                this.tasks.clear();
                this.adapter.notifyDataSetChanged();
                break;
        }
        return super.onOptionsItemSelected(item);
    }

    //wb, 15 Sep, 2017: take out the hook from checkbox
    public void clearDonetasks() {
        for (int i = 0; i < tasks.size(); i++) {
            if (tasks.get(i).isDone()) {
                tasks.get(i).setIsDone(false);
            }
        }
    }

    public void deleteDonetasks() {
        for (int i = 0; i < tasks.size(); i++) {
            if (tasks.get(i).isDone()) {
                tasks.remove(i);
            }
        }
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
        super.onCreateContextMenu(menu, v, menuInfo);

        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.context_menu, menu);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
        int position = (int) info.id;

        switch (item.getItemId()) {
            case R.id.context_delete:
                this.tasks.remove(position);
                this.adapter.notifyDataSetChanged();
                return true;
            case R.id.context_edit:
                createEditDialog(tasks.get(position));
                return true;
            default:
                return super.onContextItemSelected(item);
        }
    }

    public void createEditDialog(final Task task) {

        LayoutInflater li = LayoutInflater.from(MainActivity.this);
        View dialogView = li.inflate(R.layout.edit_dialog, null);

        AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(MainActivity.this);
        alertDialogBuilder.setView(dialogView);

        final EditText inputText = (EditText) dialogView.findViewById(R.id.edit_dialog_input);
        inputText.setText(task.getTaskContent());
        final TextView dialogMessage = (TextView) dialogView.findViewById(R.id.edit_dialog_message);

        alertDialogBuilder
                .setCancelable(true)
                .setPositiveButton("Save",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                task.setTaskContent(inputText.getText().toString());
                                sortList();
                                adapter.notifyDataSetChanged();
                            }
                        })
                .setNegativeButton("Cancel",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                dialog.cancel();
                            }
                        });

        final AlertDialog alert = alertDialogBuilder.create();
        alert.show();
    }

    /* wb, 18Sep2017: sort the tasks list */
    public void sortList() {
        Collections.sort(tasks, new Comparator<Task>() {
            @Override
            public int compare(Task content1, Task content2) {
                /* return o1.getTaskContent().compareTo(o2.getTaskContent()); */
                /* ignore case sentsitivity */
                return content1.getTaskContent().compareToIgnoreCase(content2.getTaskContent());
            }
        });
    }

}

第二个活动：

    package com.wbapps.wbshoppinglist;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.view.ContextMenu;
import android.view.LayoutInflater;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import org.xmlpull.v1.XmlPullParserException;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Created by Andreas on 9/4/2017.
 */

public class ShoppingListActivity extends AppCompatActivity {
    /*wb, 19Sep2017: Not yet
    public static final String RETVAL_KEY = "RETURN STRING";
    */
    ListView shopping_list_view;
    List<Task> tasks, shoppingTasks;
    TodoListAdapter adapter;
    XmlParser parser;
    File file;
    ActionBar actionBar;

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

        file = new File(Environment.getExternalStorageDirectory(), "tasks.xml");
        parser = new XmlParser();
        tasks = new ArrayList<Task>();
        shoppingTasks = new ArrayList<Task>();
        if (file.exists()) {
            try {
                tasks = parser.read(file);
                if (tasks.isEmpty()) {
                    Toast.makeText(this, "No Items in Shopping List", Toast.LENGTH_SHORT).show();
                    //file.delete();
                    //file.createNewFile();
                } else {
                    /*
                    Collections.sort(tasks, new Comparator<Task>() {
                        @Override
                        public int compare(Task o1, Task o2) {
                            return o1.getTaskContent().compareTo(o2.getTaskContent());
                        }
                    });
                    */
                    addDonelistitems();
                }
            } catch (XmlPullParserException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            } catch (FileNotFoundException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            } catch (IOException ex) {
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            }
        } else {
            try {
                file.createNewFile();
            } catch (IOException ex) {
                Toast.makeText(this, "Task File not existing!", Toast.LENGTH_SHORT).show();
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            }
        }

        //create an instance for the view of the lauout
        shopping_list_view = (ListView) findViewById(R.id.shoppingListView);
        registerForContextMenu(shopping_list_view);

        adapter = new TodoListAdapter(shoppingTasks, this);
        shopping_list_view.setAdapter(adapter);

        SwipeDismissListViewTouchListener touchListener =
                new SwipeDismissListViewTouchListener(
                        shopping_list_view,
                        new SwipeDismissListViewTouchListener.DismissCallbacks() {
                            @Override
                            public boolean canDismiss(int position) {
                                return true;
                            }

                            @Override
                            public void onDismiss(ListView listView, int[] reverseSortedPositions) {
                                for (int position : reverseSortedPositions) {
                                    //wb, 15Sep: With swipe an item uncheck the checkbox for this item in the file for the shopping items
                                    for (int i = 0; i < tasks.size(); i++) {
                                        if (tasks.get(i).getTaskContent() == shoppingTasks.get(position).getTaskContent()) {
                                            tasks.get(i).setIsDone(false);
                                            try {
                                                parser.write(tasks, file);
                                            } catch (IOException ex) {
                                                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
                                            }
                                        }
                                    }
                                    shoppingTasks.remove(position);
                                    adapter.notifyDataSetChanged();
                                }
                            }
                        });
        shopping_list_view.setOnTouchListener(touchListener);
       }

        @Override
        public void onBackPressed() {
            /* I jaust added a toas there to see if I will reach here */
            Toast.makeText(this, "we are in onBackPressed", Toast.LENGTH_SHORT).show();
            finish();
        }

        public void addDonelistitems() {

            for (int i = 0; i < tasks.size(); i++) {
                if (tasks.get(i).isDone() == true) {
                    shoppingTasks.add(tasks.get(i));
                }
            }
        }


    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
        super.onCreateContextMenu(menu, v, menuInfo);

        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.context_menu, menu);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
        int position = (int) info.id;

        switch (item.getItemId()) {
            case R.id.context_delete:
                this.tasks.remove(position);
                this.adapter.notifyDataSetChanged();
                return true;
            case R.id.context_edit:
                createEditDialog(tasks.get(position));
                return true;
            default:
                return super.onContextItemSelected(item);
        }
    }

    public void createEditDialog(final Task task) {

        LayoutInflater li = LayoutInflater.from(ShoppingListActivity.this);
        View dialogView = li.inflate(R.layout.edit_dialog, null);

        AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(ShoppingListActivity.this);
        alertDialogBuilder.setView(dialogView);

        final EditText inputText = (EditText) dialogView.findViewById(R.id.edit_dialog_input);
        inputText.setText(task.getTaskContent());
        final TextView dialogMessage = (TextView) dialogView.findViewById(R.id.edit_dialog_message);

        alertDialogBuilder
                .setCancelable(true)
                .setPositiveButton("Save",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                task.setTaskContent(inputText.getText().toString());
                                adapter.notifyDataSetChanged();
                            }
                        })
                .setNegativeButton("Cancel",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                dialog.cancel();
                            }
                        });

        final AlertDialog alert = alertDialogBuilder.create();
        alert.show();
    }

}

【问题讨论】：

禁用后退按钮，否则您需要为android后退按钮实现onactivityresult，并首先在该通知适配器中。
你试过 super.onBackPressed() 而不是 finish() ;
对不起 Sai，但我不明白如何处理这个 super.onBackPressed。只是代替完成（）。在我的方法“public void onBackPressed()”中？那应该是什么结果？在 xml 文件中为 isDone 值获取正确的值有什么帮助？

标签： android android-lifecycle back-button

【解决方案1】：

在今天尝试了一下之后，似乎我用后退按钮解决了我的问题。从第二个活动返回时，我似乎忘记将适配器设置为 onResume 中的 list_view。把代码改成这样后

    @Override
        protected void onResume() {
            super.onResume();
            /* Do I have to do the same here like in onCreate? It does not work yet!*/
            Toast.makeText(this, "onResume is reached!", Toast.LENGTH_SHORT).show();

            if (file.exists()) {
                try {
                    tasks = parser.read(file);
                    if (tasks.isEmpty()) {
                        file.delete();
                        file.createNewFile();
                    }else {

 ==>>new code here      adapter = new TodoListAdapter(tasks, this);
 ==>>new code here      list_view.setAdapter(adapter);

                        sortList();}
                } catch (XmlPullParserException ex) {
                    Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
                } catch (FileNotFoundException ex) {
                    Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
                } catch (IOException ex) {
                    Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
                }
            } else {
                try {
                    file.createNewFile();
                } catch (IOException ex) {
                    Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
                }
            }

        }

一切正常。我猜如果没有新代码，适配器会将旧 xml 文件中的值放到 list_view 中。

我想我必须在 android 上学到很多东西！

非常感谢所有试图帮助我的人！

无论您身在何处，都祝您有美好的一天

安德烈亚斯

【讨论】：