從資料庫中洗掉專案時如何使用自定義配接器自動更新ListView-有解無憂

我創建了一個 ListView，我為其實作了一個自定義配接器。此外，我將它連接到 SQLite 資料庫，其中包含 ListView 的內容。

我有一個包含多個專案的 ListView。每個專案都由一個 TextView 和一個用作按鈕的 ImageView 組成。當用戶單擊 ImageView 時，我想從資料庫中洗掉該專案并自動更新 ListView。

不幸的是，我只知道如何從資料庫中洗掉該專案。在專案從資料庫中洗掉后，我想不出一種自動更新程式中的 ListView 的方法。

在下面的版本中，我在 MainActivity 中為 ListView 添加了一個 onItemClickListener - 但它在用戶單擊 ImageView 時不起作用（即使 ImageView 是 ListView 的一部分）。

主要活動

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);
        }
    });
}

}

資料模型

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;
}

}

資料配接器

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;
}

}

資料庫助手

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;
    }
}

}

我感謝任何幫助或建議。如果您需要進一步解釋，請告訴我。

妮可

uj5u.com熱心網友回復：

在下面的版本中，我在 MainActivity 中為 ListView 添加了一個 onItemClickListener - 但它在用戶單擊 ImageView 時不起作用（即使 ImageView 是 ListView 的一部分）。

根據您的代碼考慮以下內容：-

作業示例

以下代碼基于您的代碼，但進行了各種更改，這些更改會在影像（單擊紫色框）時洗掉并重繪串列。

list_item.xml布局（更改為將專案突出顯示為無影像）：-

<?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類保持不變。

DatabaseHelper類已更改為 a) 不關閉資料庫（這是低效的，因為它將應用 WAL 更改，然后必須隨后打開相對資源消耗較大的資料庫）和 b) 完成后關閉所有游標和c) 利用方便的方法：-

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;
    }
}

資料配接器

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;
   }
}

注意一個重要的方面是利用標簽將點擊的視圖系結到 Todo/DataModel。
注意另一個重要因素是對 DataAdapter 的 ArrayList 實體的操作以及notifyDatasetChanged告訴配接器重建的后續操作。

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);
            }
        });
    }
}

*結果

從新安裝（空資料庫）開始，采取了以下措施：-

添加 Test001 - Test006 所以： -
單擊專案 Test003（不是紫色框（影像））
1. Toast 按預期顯示。
2. 日志包括D/CLICKACTION: Item was clicked for TitleTest003
單擊 Test003 的洗掉影像（紫色框）
1. Toast 按預期顯示 Test003 位置 2
2. 日志包括D/CLICKACTION: Image clicked for title = Test003 position 2
3. 1. ie Test003 從顯示中移除
4. 通過 App Inspection 的資料庫顯示：-
- - 即資料庫中沒有Test003行

uj5u.com熱心網友回復：

直接使用 SQLite 可能具有挑戰性，而且 ListView 已過時，不建議再使用。最佳實踐是使用 RecycleView

這是一個很好的教程如何使用它：

Room - 來自 Google 的 SQLite 包裝庫

LiveData - 用于訂閱實時更新

RecyclerView - 用于構建高效串列的 UI 小部件

轉載請註明出處，本文鏈接：https://www.uj5u.com/qiye/490803.html

標籤：爪哇安卓 sqlite 安卓-sqlite 定制适配器

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