从 RecyclerView 中删除房间条目

Posted 2023-04-18

【中文标题】从 RecyclerView 中删除房间条目

【英文标题】：Deleting Room entry from RecyclerView

【发布时间】：2018-09-01 05:41:25

【问题描述】：

我是编程新手，我跟随this tutorial 使用适配器创建了RecyclerView。我不知道如何使用我的 Dao 中的删除功能与每个条目旁边的 ImageButton. 相关。另外，这是我的第一个应用程序，所以当您看到“.allowMainThreadQueries”之类的内容时，请多多关照。

带有 recyclerview 的活动：

public class DatabaseActivity extends AppCompatActivity 

    RecyclerView recyclerView;
    RecyclerView.Adapter adapter;
    FloatingActionButton fab;
    ImageButton delete;

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

        recyclerView = findViewById(R.id.recycler_view);

        AppDatabase db = Room.databaseBuilder(getApplicationContext(), AppDatabase.class, "production").allowMainThreadQueries().build();

        final List<Student> students = db.studentDao().getAllUsers();

        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        adapter = new StudentAdapter(students);
        recyclerView.setAdapter(adapter);

        fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() 
            @Override
            public void onClick(View v) 
                startActivity(new Intent(DatabaseActivity.this, DatabaseAddActivity.class));
            
        );
    

适配器：

class StudentAdapter extends RecyclerView.Adapter<StudentAdapter.ViewHolder> 

    List<Student> students;

    public StudentAdapter(List<Student> students) 
        this.students = students;
    

    @Override
    public StudentAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) 
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.student_row, parent, false);
        return new ViewHolder(view);
    

    @Override
    public void onBindViewHolder(StudentAdapter.ViewHolder holder, int position) 
        holder.first_name.setText(students.get(position).getFirstName());
        holder.last_name.setText(students.get(position).getLastName());
        holder.email.setText(students.get(position).getEmail());
    

    //See how many items need to be displayed
    @Override
    public int getItemCount() 

        return students.size();
    

    public class ViewHolder extends RecyclerView.ViewHolder 
        public TextView first_name;
        public TextView last_name;
        public TextView email;
        public ImageButton delete;

        //What we are showing in the viewholder
        public ViewHolder(View itemView) 
            super(itemView);
            first_name = itemView.findViewById(R.id.first_name);
            last_name = itemView.findViewById(R.id.last_name);
            email = itemView.findViewById(R.id.email);
            delete = itemView.findViewById(R.id.delete);
        
    

道：

@Dao
public interface StudentDao 
@Query("SELECT * FROM student ")
List<Student> getAllUsers();

@Query("SELECT * FROM student WHERE monday = 1")
List<Student> getMonday();

@Query("SELECT * FROM student WHERE tuesday = 1")
List<Student> getTuesday();

@Query("SELECT * FROM student WHERE wednesday = 1")
List<Student> getWednesday();

@Query("SELECT * FROM student WHERE thursday = 1")
List<Student> getThursday();

@Query("SELECT * FROM student WHERE friday = 1")
List<Student> getFriday();

@Insert
void insertAll(Student... students);

@Delete
void delete(Student student);

@Update
void updateStudent(Student student);

学生地址：

public class DatabaseAddActivity extends AppCompatActivity 

//Calling needed resources
EditText firstName;
EditText lastName;
EditText email;
Button button;
CheckBox monday, tuesday, wednesday, thursday, friday;


//Defining which view.xml file to use
@Override
protected void onCreate(Bundle savedInstanceState) 
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_database_add);

    //Using resources to find using .xml setup
    firstName = findViewById(R.id.first_name);
    lastName = findViewById(R.id.last_name);
    email = findViewById(R.id.email);
    monday = findViewById(R.id.monday_switch);
    tuesday = findViewById(R.id.tuesday_switch);
    wednesday = findViewById(R.id.wednesday_switch);
    thursday = findViewById(R.id.thursday_switch);
    friday = findViewById(R.id.friday_switch);
    button = findViewById(R.id.button_add);

    //What happens when button is pressed
    button.setOnClickListener(new View.OnClickListener() 
        @Override
        public void onClick(View v) 

            AppDatabase db = Room.databaseBuilder(getApplicationContext(), AppDatabase.class, "production").allowMainThreadQueries().build();
            Boolean mondayState = monday.isChecked();
            Boolean tuesdayState = tuesday.isChecked();
            Boolean wednesdayState = wednesday.isChecked();
            Boolean thursdayState = thursday.isChecked();
            Boolean fridayState = friday.isChecked();

            Student student = new Student(firstName.getText().toString(), lastName.getText().toString(), email.getText().toString(), mondayState, tuesdayState, wednesdayState, thursdayState, fridayState);
            db.studentDao().insertAll(student);
            startActivity(new Intent(DatabaseAddActivity.this,DatabaseActivity.class));
        
    );

【问题讨论】：

您能出示您的Dao 代码吗？你有没有看过：developer.android.com/reference/android/arch/persistence/room/…

就是这样。我确实看过，但仍然没有线索。

【参考方案1】：

在DatabaseActivity：

adapter = new StudentAdapter(db, students);

更新

在您的 Adapter 类中：

AppDatabase db;
List<Student> students;

public StudentAdapter(AppDatabase db, List<Student> students) 
    this.db = db;
    this.students = students;


@Override
public void onBindViewHolder(StudentAdapter.ViewHolder holder, int position) 
    Student student = students.get(position);
    holder.first_name.setText(students.get(position).getFirstName());
    holder.last_name.setText(students.get(position).getLastName());
    holder.email.setText(students.get(position).getEmail());
    holder.delete.setOnClickListener.setOnClickListener(new View.OnClickListener() 
            @Override
            public void onClick(View view) 
                db.delete(student);
                students.remove(student);
                notifyItemRemoved(position);
            
        );

【讨论】：

我试过这个。它没有删除，所以我检查了日志，它说“没有向 HAL 提供足够的数据，预期位置 11857215 ，只写了 11856960”。我不知道这是否重要，但是是的。此外，新条目现在会覆盖旧条目

@Philedor 向您的学生展示在活动中添加代码？

添加到主评论

@Philedor 我忘了在删除onClick() 方法中在db.delete(student); 之后添加这个笔划students.remove(student);