从数据库删除项目时，如何使用自定义适配器自动更新ListView

Question

我创建了一个listView，并为其实现了一个自定义适配器。另外，我将其连接到SQLite数据库，该数据库包含ListView的内容。

我有一个带有几个项目的ListView。每个项目都由一个文本视图和一个功能作为按钮的imageView组成。当用户单击ImageView时，我想从数据库中删除该项目，并自动更新ListView。

不幸的是，我只知道如何从数据库中删除项目。从数据库中删除该项目后，我想不出一种方法可以自动更新程序中的ListView。

在下面的版本中，我在MainActivity中为ListView添加了一个OnItemClickListener-但对于用户单击imageView时，它不适（即使ImageView是ListView的一部分）。

MainActivity

public class MainActivity extends AppCompatActivity {
//References to buttons and other controls on the layout
private Button btn_add;
private EditText et_todo;
private Switch sw;
private static ListView lv;
private static DataAdapter todoAdapter;
private DataBaseHelper dbHelper;

/**
 * Initialization Method
 *
 * @param savedInstanceState
 */
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    dbHelper = new DataBaseHelper(MainActivity.this);

    assignVariables();
    registerClick();
    showAllToDos(dbHelper);
}

private void assignVariables() {
    //assign values to variables
    btn_add = (Button) findViewById(R.id.btn_add);
    et_todo = (EditText) findViewById(R.id.et_todo);
    lv = (ListView) findViewById(R.id.lv);
}

public void showAllToDos(DataBaseHelper dbHelper) {
    todoAdapter = new DataAdapter(MainActivity.this, R.layout.list_item, dbHelper.getAllAsList(), dbHelper);
    lv.setAdapter(todoAdapter);
}

private void registerClick() {
    btn_add.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            String toDoTitle = et_todo.getText().toString();

            if(Pattern.matches("s*", toDoTitle)) {
                Toast.makeText(MainActivity.this, "Title is missing", Toast.LENGTH_SHORT).show();
            } else if(dbHelper.existsInDB(new DataModel(toDoTitle))) {
                Toast.makeText(MainActivity.this, "Already added as ToDo", Toast.LENGTH_SHORT).show();
            } else {
                DataModel dModel = new DataModel(toDoTitle);
                dbHelper.addOne(dModel);

                showAllToDos(dbHelper);
            }
            //empty input field
            et_todo.setText("");
        }
    });

    lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
            DataModel clickedItem = (DataModel) adapterView.getItemAtPosition(position);
            dbHelper.deleteOne(clickedItem);

            showAllToDos(dbHelper);
        }
    });
}

}

datamodel

public class DataModel {

//Attributes
private int id;
private String title;

//Constructors
public DataModel(String title) {
    this.title = title;
}

public DataModel() {

}

//toString
@Override
public String toString() {
    return "DataModel{" +
            "id=" + id +
            ", title='" + title + '\'' +
            '}';
}

//Getters and Setters
public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getTitle() {
    return title;
}

public void setTitle(String title) {
    this.title = title;
}

}

dataAdapter

public class DataAdapter extends ArrayAdapter<DataModel> {

/**
 * Attributes
 */
private Context mContext;
private int mResource;
private ArrayList<DataModel> mList;
private DataBaseHelper mDbHelper;


public DataAdapter(Context context, int resource, ArrayList<DataModel> list, DataBaseHelper dbHelper) {
    super(context, resource, list);
    mContext = context;
    mResource = resource;
    mList = list;
    mDbHelper = dbHelper;
}

public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    //get the objects information
    String title = getItem(position).getTitle();

    //create object with the information
    DataModel model = new DataModel(title);

    LayoutInflater inflater = LayoutInflater.from(mContext);
    convertView = inflater.inflate(mResource, parent, false);

    //get TextViews
    TextView tvTitle = (TextView) convertView.findViewById(R.id.task);

    //set information to TextViews
    tvTitle.setText(title);

    //delete function
    ImageView delView = (ImageView) convertView.findViewById(R.id.delView);
    delView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            mDbHelper.deleteOne(model);
        }
    });
    return convertView;
}

}

databaseHelper

public class DataBaseHelper extends SQLiteOpenHelper {

public static final String TODO_TABLE = "TODO_TABLE";
public static final String COLUMN_ID = "ID";
public static final String COLUMN_TODO_TITLE = "TODO_TITLE";
private Context mContext;

public DataBaseHelper(@Nullable Context context) {
    super(context, "todo.db", null, 1);
    mContext = context;
}

/**
 * Is called when the app requests or inputs new data.
 *
 * @param db
 */
@Override
public void onCreate(SQLiteDatabase db) {

    String createTableStatement = "CREATE TABLE " + TODO_TABLE
            + " (" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + COLUMN_TODO_TITLE + " TEXT)";

    db.execSQL(createTableStatement);
    //create new Table
}

/**
 * Called whenever the database version number changes.
 * Prevents the previous apps from crashing.
 *
 * @param sqLiteDatabase
 * @param i
 * @param i1
 */
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

}

/**
 * method to add new database entry
 *
 * @param dModel
 * @return
 */
public boolean addOne(DataModel dModel) {
    SQLiteDatabase db = this.getWritableDatabase(); //for insert actions
    ContentValues cv = new ContentValues(); //Content values stores data in pairs

    cv.put(COLUMN_TODO_TITLE, dModel.getTitle());

    long insert = db.insert(TODO_TABLE, null, cv);

    //clean up, close connection to database and cursor
    db.close();
    if(insert == -1) { //if insert is negative number than insert went wrong
        return false;
    } else { //if insert is positive number than insert succeeded
        return true;
    }
}

public boolean deleteOne(DataModel dModel) {
    //if DataModel is found in the database, delete it and return true
    //if it is not found, return false
    SQLiteDatabase db = this.getWritableDatabase();

    String queryString = "DELETE FROM " + TODO_TABLE
            + " WHERE " + COLUMN_TODO_TITLE + " = " + "\"" + dModel.getTitle() + "\"";;

    Cursor cursor = db.rawQuery(queryString, null);

    if(cursor.moveToFirst()) {
        return true;
    } else {
        return false;
    }
}

public ArrayList<DataModel> getAllAsList() {
    //create empty list
    ArrayList<DataModel> returnList = new ArrayList<>();
    //get data from the database
    String queryString = "SELECT * FROM " + TODO_TABLE;
    SQLiteDatabase db = this.getReadableDatabase(); //get data from database
    Cursor cursor = db.rawQuery(queryString, null);

    if(cursor.moveToFirst()) { //returns a true if there were items selected
        //loop through results, create new todo objects, put them into return list
        do {
            String todoTitle = cursor.getString(1);

            DataModel newTodo = new DataModel(todoTitle);
            returnList.add(newTodo);

        } while(cursor.moveToNext());
    } else { //returns a false if no items were selected
        //failure, to not add anything to the list
    }

    //clean up, close connection to database and cursor
    cursor.close();
    db.close();

    return returnList;
}

public boolean existsInDB(DataModel dModel) {
    SQLiteDatabase db = this.getWritableDatabase(); //for insert actions
    String queryString = "SELECT * FROM " + TODO_TABLE
            + " WHERE " + COLUMN_TODO_TITLE + " = " + "\"" + dModel.getTitle() + "\"";

    Cursor cursor = db.rawQuery(queryString, null);

    if(cursor.moveToFirst()) {
        return true;
    } else {
        return false;
    }
}

}

我感谢任何帮助或建议。 让我知道，如果您需要进一步的解释。

妮可

Answer 1

在下面的版本中，我在MainActivity中为ListView添加了一个OnItemClickListener-但对于用户单击imageView时，它不起作用（即使ImageView是ListView的一部分）。

。

根据您的代码考虑以下内容： -

工作示例

以下代码基于您的代码，但在图像（单击紫色的框）时进行了各种更改并删除列表。

list_item.xml 布局（更改为无图像以突出显示项目）： -

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:background="@color/teal_200">
    <TextView
        android:id="@+id/task"
        android:layout_width="400dp"
        android:layout_height="match_parent"
        >
    </TextView>
    <ImageView
        android:id="@+id/delView"
        android:layout_width="100dp"
        android:layout_height="20dp"
        android:layout_gravity="center"
        android:background="@color/purple_200"
        >
    </ImageView>
</LinearLayout>

datamodel 类是不变的。

databasehelper 类已更改为a）不关闭数据库（这是效率低下的，因为它将应用WAL更改，然后必须打开databaset，该数据库相对昂贵，b）使用和c）使用便利方法时所有光标： -

public class DataBaseHelper extends SQLiteOpenHelper {

    public static final String TODO_TABLE = "TODO_TABLE";
    public static final String COLUMN_ID = "ID";
    public static final String COLUMN_TODO_TITLE = "TODO_TITLE";
    private Context mContext;

    public DataBaseHelper(@Nullable Context context) {
        super(context, "todo.db", null, 1);
        mContext = context;
    }
    
    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTableStatement = "CREATE TABLE " + TODO_TABLE
                + " (" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
                + COLUMN_TODO_TITLE + " TEXT)";

        db.execSQL(createTableStatement);
    }
    
    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }
    
    public boolean addOne(DataModel dModel) {
        SQLiteDatabase db = this.getWritableDatabase(); //for insert actions
        ContentValues cv = new ContentValues(); //Content values stores data in pairs
        cv.put(COLUMN_TODO_TITLE, dModel.getTitle());
        return db.insert(TODO_TABLE, null, cv) > -1;
    }

    public boolean deleteOne(DataModel dModel) {
        SQLiteDatabase db = this.getWritableDatabase();
        return db.delete(TODO_TABLE,COLUMN_TODO_TITLE +"=?",new String[]{dModel.getTitle()}) > 0;
    }

    @SuppressLint("Range")
    public ArrayList<DataModel> getAllAsList() {
        //create empty list
        ArrayList<DataModel> returnList = new ArrayList<>();
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.query(TODO_TABLE,null,null,null,null,null,null);
        while (cursor.moveToNext()) {
            returnList.add(new DataModel(cursor.getString(cursor.getColumnIndex(COLUMN_TODO_TITLE))));
        }
        cursor.close();
        return returnList;
    }

    public boolean existsInDB(DataModel dModel) {
        boolean rv = false;
        SQLiteDatabase db = this.getWritableDatabase(); //for insert actions
        Cursor cursor = db.query(TODO_TABLE,null,COLUMN_TODO_TITLE+"=?",new String[]{dModel.getTitle()},null,null,null);
        if(cursor.moveToFirst()) {
            rv = true;
        }
        cursor.close();
        return rv;
    }
}

dataAdapter

public class DataAdapter extends ArrayAdapter<DataModel> {

   /**
    * Attributes
    */
   private Context mContext;
   private int mResource;
   private ArrayList<DataModel> mList;
   private DataBaseHelper mDbHelper;


   public DataAdapter(Context context, int resource, ArrayList<DataModel> list, DataBaseHelper dbHelper) {
      super(context, resource, list);
      mContext = context;
      mResource = resource;
      mList = list;
      mDbHelper = dbHelper;
   }

   public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
      //get the objects information
      String title = getItem(position).getTitle();

      //create object with the information
      DataModel model = new DataModel(title);

      LayoutInflater inflater = LayoutInflater.from(mContext);
      convertView = inflater.inflate(mResource, parent, false);

      //get TextViews
      TextView tvTitle = (TextView) convertView.findViewById(R.id.task);

      //set information to TextViews
      tvTitle.setText(title);

      //delete function
      ImageView delView = (ImageView) convertView.findViewById(R.id.delView);
      delView.setTag(position); //<<<<< ADDDED Sets the tag with the position in the list
      delView.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View view) {
            Integer position = new Integer(view.getTag().toString()); // gets the position from the tag
            DataModel model = mList.get(position); // gets the respective DataModel from the ArrayList
            Toast.makeText(view.getContext(),"You clicked the Image for Title = " + model.getTitle() + " position " + view.getTag(),Toast.LENGTH_SHORT).show();
            Log.d("CLICKACTION","Image clicked for title = " + model.getTitle() + " position " + view.getTag());
            /* probably faster but the potential for issues if for some reason deletes other than expected
            if (mDbHelper.deleteOne(model)) {
               mList.remove(model);
               notifyDataSetChanged();
            }
             */
            /* Alternative approach - more intensive but the resultant list IS accurate */
            mDbHelper.deleteOne(model);
            ArrayList<DataModel> newlist = mDbHelper.getAllAsList();
            mList.clear();
            for (DataModel dm: newlist) {
               mList.add(dm);
               notifyDataSetChanged();
            }
         }
      });
      return convertView;
   }
}

• 注意一个重要方面是利用标签将单击视图绑定到todo/dataModel。
• 注意另一个重要因素是操纵DataAdapter的ArrayList实例和后续的notifyDataSetchanged，它告诉适配器重建。

和 MainActivity ： -

public class MainActivity extends AppCompatActivity {
    //References to buttons and other controls on the layout
    private Button btn_add;
    private EditText et_todo;
    private Switch sw;
    private static ListView lv;
    private static DataAdapter todoAdapter;
    private DataBaseHelper dbHelper;

    /**
     * Initialization Method
     *
     * @param savedInstanceState
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dbHelper = new DataBaseHelper(MainActivity.this);

        assignVariables();
        registerClick();
        showAllToDos(dbHelper); // creates a new instance of the adapter each time it is called
    }


    private void assignVariables() {
        //assign values to variables
        btn_add = (Button) findViewById(R.id.btn_add);
        et_todo = (EditText) findViewById(R.id.et_todo);
        lv = (ListView) findViewById(R.id.lv);
    }

    public void showAllToDos(DataBaseHelper dbHelper) {
        todoAdapter = new DataAdapter(MainActivity.this, R.layout.list_item, dbHelper.getAllAsList(), dbHelper);
        lv.setAdapter(todoAdapter);
    }
    
    private void registerClick() {
        btn_add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String toDoTitle = et_todo.getText().toString();

                if(Pattern.matches("s*", toDoTitle)) {
                    Toast.makeText(MainActivity.this, "Title is missing", Toast.LENGTH_SHORT).show();
                } else if(dbHelper.existsInDB(new DataModel(toDoTitle))) {
                    Toast.makeText(MainActivity.this, "Already added as ToDo", Toast.LENGTH_SHORT).show();
                } else {
                    DataModel dModel = new DataModel(toDoTitle);
                    dbHelper.addOne(dModel);

                    showAllToDos(dbHelper);
                }
                //empty input field
                et_todo.setText("");
            }
        });


        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
                Toast.makeText(view.getContext(),"Item was clicked for Title = " + ((DataModel) adapterView.getItemAtPosition(position)).getTitle(),Toast.LENGTH_SHORT).show();
                Log.d("CLICKACTION","Item was clicked for Title" + ((DataModel) adapterView.getItemAtPosition(position)).getTitle());
                //DataModel clickedItem = (DataModel) adapterView.getItemAtPosition(position);
                //dbHelper.deleteOne(clickedItem);
                //showAllToDos(dbHelper);
            }
        });
    }
}

*结果

来自新的安装（空数据库），然后采取以下操作： -

1. 添加test001-test006 so： -

   1. 

2. 单击项目test003（不是紫色框（图像））

   1. 敬酒如预期的。
   2. 日志包括d/clickaction：单击titletest003

   的项目

3. 单击删除图像（紫色框）以进行测试003

   1. 敬酒显示为预期的测试003位置2
   2. 日志包括d/clickAction：图像单击标题= test003位置2
   3. 
      1. IE Test003从显示器中删除
   4. 通过应用程序检查数据库显示： -
   • 
     • IE数据库中的No Test003行

Answer 2

直接使用sqlite可能具有挑战性，也不建议再使用listView。最好的做法是在这里使用RecycleView

是一个很好的教程，全部使用它：

Room - Google的Sqlite包装库

livedata>

="https://developer.android.com/guide/topics/ui/layout/recyclerview?gclid=Cj0KCQjw-pCVBhCFARIsAGMxhAecKzLSA4G5a_hqcD9ZqkSCKhqLIzykl6Gu0GIBtC0UJGJrRMp25eQaArBoEALw_wcB&gclsrc=aw.ds" rel="nofollow noreferrer">RecyclerView - UI widget for建筑有效列表