Android：如何从保存在 SQLite 数据库中的列表视图中删除项目？

Question

我必须从保存在 SQLite 数据库中的列表视图中删除一个项目。我可以使用搜索“EditText”来做到这一点，但我只需要单击它们即可删除行。 这是我的代码：

DBHelper：

public class EventDbHelper extends SQLiteOpenHelper {

private static final String DATABASE_NAME = "USERINFO.DB";
private static final int DATABASE_VERSION = 1;
private static final String CREATE_QUERY =
        "CREATE TABLE "+ Event.NewEventInfo.TABLE_NAME+"("+
                Event.NewEventInfo.NAME+" TEXT,"+
                Event.NewEventInfo.YEAR+" TEXT,"+
                Event.NewEventInfo.MONTH+" TEXT,"+
                Event.NewEventInfo.DAY+" TEXT,"+
                Event.NewEventInfo.HOUR+" TEXT,"+
                Event.NewEventInfo.MINUTE+" TEXT);";

public EventDbHelper(Context context){

    super(context,DATABASE_NAME,null,DATABASE_VERSION);
    Log.e("DATABASE OPERATIONS","Database created/opened...");

}

@Override
public void onCreate(SQLiteDatabase db) {

    db.execSQL(CREATE_QUERY);
    Log.e("DATABASE OPERATIONS","Table created...");

}

public void addInformation (String name,String year,String month,String day,String hour,String minute,SQLiteDatabase db)
{
    ContentValues contentValues=new ContentValues();
    contentValues.put(Event.NewEventInfo.NAME,name);
    contentValues.put(Event.NewEventInfo.YEAR,year);
    contentValues.put(Event.NewEventInfo.MONTH,month);
    contentValues.put(Event.NewEventInfo.DAY,day);
    contentValues.put(Event.NewEventInfo.HOUR,hour);
    contentValues.put(Event.NewEventInfo.MINUTE,minute);
    db.insert(Event.NewEventInfo.TABLE_NAME,null,contentValues);
    Log.e("DATABASE OPERATIONS","One row inserted...");
}

public Cursor getInformation (SQLiteDatabase db)
{
    Cursor cursor;
    String[] projections = {Event.NewEventInfo.NAME, Event.NewEventInfo.YEAR, Event.NewEventInfo.MONTH,
            Event.NewEventInfo.DAY, Event.NewEventInfo.HOUR, Event.NewEventInfo.MINUTE};
    cursor = db.query(Event.NewEventInfo.TABLE_NAME,projections,null,null,null,null,null);
    return cursor;

}



public void deleteInformation(String name, SQLiteDatabase db)
{
    String selection = Event.NewEventInfo.NAME+" LIKE ?";
    String[] selection_args = {name};
    db.delete(Event.NewEventInfo.TABLE_NAME,selection,selection_args);
}




@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}
}

主活动：

 public void deleteEvent (View view)
{
    search_name=et.getText().toString();
    eventDbHelper= new EventDbHelper(getApplicationContext());
    sqLiteDatabase= eventDbHelper.getReadableDatabase();
    eventDbHelper.deleteInformation(search_name, sqLiteDatabase);
    Toast.makeText(getApplicationContext(),"Event  deleted",Toast.LENGTH_SHORT).show();
    finish();
    startActivity(getIntent());

}

ListDataAdapterActivity：

public class ListDataAdapter extends ArrayAdapter {
List list = new ArrayList();
public ListDataAdapter(Context context, int resource) {
    super(context, resource);
}

static class LayoutHandler
{
    TextView NAME,DAYS,HOURS,MINUTES,SECONDS;

}

@Override
public void add(Object object) {
    super.add(object);
    list.add(object);
}

@Override
public int getCount() {
    return list.size();
}

@Override
public Object getItem(int position) {
    return list.get(position);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    View row = convertView;
    LayoutHandler layoutHandler;
    if(row == null)
    {
        LayoutInflater layoutInflater =(LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        row = layoutInflater.inflate(R.layout.list_item,parent,false);
        layoutHandler = new LayoutHandler();
        layoutHandler.NAME = (TextView) row.findViewById(R.id.text_name);
        layoutHandler.DAYS = (TextView) row.findViewById(R.id.days_list_item);
        layoutHandler.HOURS = (TextView) row.findViewById(R.id.hours_list_item);
        layoutHandler.MINUTES = (TextView) row.findViewById(R.id.minutes_list_item);
        //layoutHandler.SECONDS = (TextView) row.findViewById(R.id.seconds_list_item);
        row.setTag(layoutHandler);
    }

    else{

        layoutHandler =(LayoutHandler) row.getTag();

    }

    DataProvider dataProvider =(DataProvider) this.getItem(position);
    layoutHandler.NAME.setText(dataProvider.getName());
    layoutHandler.DAYS.setText(dataProvider.getsDays());
    layoutHandler.HOURS.setText(dataProvider.getsHours());
    layoutHandler.MINUTES.setText(dataProvider.getsMinutes());
    //layoutHandler.SECONDS.setText(dataProvider.getsSeconds());

    return row;
}

}

我应该编辑什么？

Answer 1

这是一个由 SQLite 数据库填充的列表视图的简单示例。

我只会解释如何读取信息以及之后如何删除一行。

首先，您必须为要列出的对象创建一个模式（可选）。列表视图也可以由字符串列表或原始变量类型填充。

让我们创建一个包含名称和简短描述的类别模式。它包含字段、构造函数、getter 和 setter：

public class Category {

    //Fields
    private int id;
    private String name;
    private String description;

    //Constructors
    public Category()
    {

    }

    public Category(String name, String description)
    {
        this.name = name;
        this.description = description;
    }

    public Category(int id, String name, String description)
    {
        this.id = id;
        this.name = name;
        this.description = description;
    }

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

    public void setName(String name)
    {
        this.name = name;
    }

    public void setDescription(String description)
    {
        this.description = description;
    }

    //Getters
    public int getId()
    {
        return this.id;
    }

    public String getName()
    {
        return this.name;
    }

    public String getDescription()
    {
        return this.description;
    }

}

我们将使用类别列表填充我们的 listView。此列表从数据库中获取信息。

最后，您需要创建一个自定义适配器（或使用预定义的适配器）将每个类别项链接到一个 xml 布局文件。

public class CategoryAdapter extends BaseAdapter {

    private Activity activity;
    private LayoutInflater inflater;
    private List<Category> items;

    public CategoryAdapter(Activity activity, List<Category> items) {
        this.activity = activity;
        this.items = items;
    }

    @Override
    public int getCount() {
        return items.size();
    }

    @Override
    public Object getItem(int location) {
        return items.get(location);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        if (inflater == null)
            inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        if (convertView == null)
            convertView = inflater.inflate(R.layout.item_category, null);

        TextView tvName = (TextView) convertView.findViewById(R.id.tvName);
        TextView tvDescription = (TextView) convertView.findViewById(R.id.tvDescription);

        // getting product data for the row
        Category c = items.get(position);

        // name
        tvName.setText(c.getName());

        // description
        tvDescription.setText(String.valueOf(c.getDescription()));

        return convertView;
    }

}

XML

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/tvName"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"
        android:textStyle="bold"/>

    <TextView
        android:id="@+id/tvDescription"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"
        android:textColor="@color/gray"/>

</LinearLayout>

是时候将适配器和类别列表链接到列表视图了。

db = new DatabaseHelper(getApplicationContext());
categories = new ArrayList<>();
categories = db.getAllCategories();
db.closeDB();

//The category adapter links the list of categories to the listview
lvCategories = (ListView) findViewById(R.id.lvCategories);
adapter = new CategoryAdapter(this, categories);
lvCategories.setAdapter(adapter);

这个简短教程的最后一部分展示了如何在长按项目时删除一行。弹出窗口要求用户确认操作。

        //onLongClick : delete item
        lvCategories.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override
            public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {

                try {
                    final Category category = (Category) parent.getItemAtPosition(position);

                    //Open dialog box
                    AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(c);

                    alertDialogBuilder
                            .setPositiveButton(R.string.confirm, new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog, int id) {

                                    //Delete client by id
                                    db.deleteCategory(category.getId());

                                    //Confirmation message
                                    Toast.makeText(c, R.string.delete_category_successfull, Toast.LENGTH_SHORT).show();

                                    //Rafraîchir la liste
                                    onResume();

                                }
                            })
                            .setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog, int id) {
                                    //Cancel operation

                                }
                                // Create the AlertDialog object and return it
                                // return builder.create();
                            })
                            .setTitle(getString(R.string.delete))
                            .setMessage(getString(R.string.delete_category, category.getName()))
                            .create();

                    alertDialogBuilder.show();

                } catch (Exception e) {
                    Toast.makeText(c, String.valueOf(e), Toast.LENGTH_LONG).show();
                }


                return true;
            }

        });

继续

categories = db.getAllCategories();
db.closeDB();

adapter = new CategoryAdapter(this, categories);
lvCategories.setAdapter(adapter);

这里是来自 DatabaseHelper 的 getAllCategories 和 deleteCategory 查询：

/*
 * getting all categories
 * */
public List<Category> getAllCategories() {
    List<Category> categories = new ArrayList<Category>();
    String selectQuery = "SELECT  * FROM " + TABLE_CATEGORIES;

    Log.e(LOG, selectQuery);

    SQLiteDatabase db = this.getReadableDatabase();
    Cursor c = db.rawQuery(selectQuery, null);

    // looping through all rows and adding to list
    if (c.moveToFirst()) {
        do {
            Category category = new Category();
            category.setId(Integer.parseInt(c.getString(c.getColumnIndex(ID))));
            category.setName(c.getString((c.getColumnIndex(CATEGORY_NAME))));
            category.setDescription((c.getString(c.getColumnIndex(CATEGORY_DESCRIPTION))));

            // adding to clients list
            categories.add(category);
        } while (c.moveToNext());
    }

    return categories;
}


/*
 * Deleting a category
 */
public void deleteCategory(int category_id) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_CATEGORIES, ID + " = ?",
            new String[] { String.valueOf(category_id) });
}

不要害羞地询问您是否需要进一步的帮助才能在数据库中插入项目、更新它们或其他任何事情！

Answer 2

您应该使用适配器来链接 xml 布局文件和对象元素列表，以分别显示项目并填充列表视图。

然后，删除数据库中的项目并刷新列表。