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java - 删除房间内数据库

问题描述

我正在学习房间数据库！！我知道如何将房间数据库中的数据插入和检索到回收站视图！但在删除操作中，我收到“没有附加适配器跳过布局！”的错误。

当有人点击回收站视图上的删除按钮时，我想要什么。任务应该被删除

这就是为什么我还在Interface中使用delete方法并在Recycler View Adapter中添加Interface，它会回调MainActivity，以便我们删除和更新recycler视图

我所有的代码都在下面给出

这是我命名为任务的实体类

@Entity
public class Task implements Serializable {
    @PrimaryKey(autoGenerate =  true)
    private int id;
    @ColumnInfo(name = "task_name")
    private String task_name;
    @ColumnInfo
    private String task_desc;
    @ColumnInfo
    private String comment;

    @ColumnInfo
    private String task_comp_date;
    @ColumnInfo
    private String activate;



    public int getId() {
        return id;
    }

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

    public String getTask_name() {
        return task_name;
    }

    public void setTask_name(String task_name) {
        this.task_name = task_name;
    }

    public String getTask_desc() {
        return task_desc;
    }

    public void setTask_desc(String task_desc) {
        this.task_desc = task_desc;
    }

    public String getTask_comp_date() {
        return task_comp_date;
    }

    public void setTask_comp_date(String task_comp_date) {
        this.task_comp_date = task_comp_date;
    }

    public String getComment() {
        return comment;
    }

    public void setComment(String comment) {
        this.comment = comment;
    }

    public String getActivate() {
        return activate;
    }

    public void setActivate(String activate) {
        this.activate = activate;
    }


}

我的名为 TaskDao 的数据访问对象

@Dao
public interface TaskDao {
    @Query("SELECT * FROM task")
    List<Task> getAll();
    @Insert
    void insert(Task task);
    @Delete
    void delete(Task task);
    @Update
    void update(Task task);
}

我的数据库

@Database(entities = {Task.class},version = 1)
public abstract class AppDataBase extends RoomDatabase {
    public abstract TaskDao taskDao();


}

我的 DataBaseClient 命名为 DatabaseClient

public class DatabaseClient {
    private Context context;
    private static DatabaseClient mInstace;

    private AppDataBase appDataBase;

    public DatabaseClient(Context context) {
        this.context = context;
        appDataBase = Room.databaseBuilder(context,AppDataBase.class,"MyDailyTask").build();
    }
    public static synchronized DatabaseClient getInstance(Context context)
    {
        if(mInstace == null)
        {
            mInstace = new DatabaseClient(context);
        }
        return mInstace;
    }
    public AppDataBase getAppDataBase()
    {
        return appDataBase;
    }
}

我的 RecyclerView 适配器

        public class TaskAdapter extends RecyclerView.Adapter<TaskAdapter.MyViewHolder> {
private Context context;
private List<Task> taskList;
public interface OnDeleteClickListener
    {
        void OnDeleteClickListener(Task task);
    }
    private OnDeleteClickListener onDeleteClickListener;

    public TaskAdapter(Context context, List<Task> taskList) {
        this.context = context;
        this.taskList = taskList;
    }

    public void setOnDeleteClickListener(OnDeleteClickListener onDeleteClickListener) {
        this.onDeleteClickListener = onDeleteClickListener;
    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view;
       view = LayoutInflater.from(context).inflate(R.layout.view_task_list,parent,false);
       MyViewHolder myViewHolder = new MyViewHolder(view);
       return myViewHolder;
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
       holder.setData(taskList.get(position).getTask_name(),taskList.get(position).getTask_desc(),taskList.get(position).getComment(),taskList.get(position).getTask_comp_date(),position);
    }

    @Override
    public int getItemCount() {
        return taskList.size();
    }

    class MyViewHolder extends RecyclerView.ViewHolder {

        private TextView t1,t2,t3,t4,t5;
        private ImageView view;
        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            t1= itemView.findViewById(R.id.tvCommnt);
            t2=itemView.findViewById(R.id.tvDesc);
            t3=itemView.findViewById(R.id.tvName);
            t4= itemView.findViewById(R.id.tvStart);
            t5 = itemView.findViewById(R.id.tvEnd);
            view =itemView.findViewById(R.id.tvdele);


        }
        public void  setData(String t01, String t02, String t03, String t05, final int position)
        {
            t1.setText("Task Comment               "+t03);
            t2.setText("Task Description           "+t02);
            t3.setText("Task Name                    "+ t01);
            t4.setText("Start  ");
            t5.setText("Ënd    "+t05);
            view.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if(onDeleteClickListener!=null)
                    {
                        onDeleteClickListener.OnDeleteClickListener(taskList.get(position));
                        taskList.remove(position);
                        notifyDataSetChanged();
                    }
                }
            });

        }
    }
}

MainActivity.java ：

  public class MainActivity extends AppCompatActivity {

       private RecyclerView recyclerView;
       ImageView imageView;
       @Override
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_main);
           imageView = findViewById(R.id.ivAdd);
           recyclerView = findViewById(R.id.rvTask);
           imageView.setOnClickListener(new View.OnClickListener() {
               @Override
               public void onClick(View v) {
                   startActivity(new Intent(getApplicationContext(), AddTaskActivity.class));
               }
           });
           new newTask().execute();
       }

class newTask extends AsyncTask<Void,Void, List<Task>> implements TaskAdapter.OnDeleteClickListener {
    List<Task> tasks;
    @Override
    protected List<Task> doInBackground(Void... voids) {

         tasks = DatabaseClient.getInstance(getApplicationContext()).getAppDataBase().taskDao().getAll();

        return  tasks;
    }

    @Override
    protected void onPostExecute(List<Task> tasks) {
        super.onPostExecute(tasks);
        TaskAdapter taskAdapter = new TaskAdapter(MainActivity.this,tasks);
        LinearLayoutManager layoutManager = new LinearLayoutManager(MainActivity.this);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.addItemDecoration(new DividerItemDecoration(getApplicationContext(),DividerItemDecoration.VERTICAL));
        recyclerView.setAdapter(taskAdapter);
        taskAdapter.setOnDeleteClickListener(this);

    }

    @Override
    public void OnDeleteClickListener(final Task task) {
new Handler().postDelayed(new Runnable() {
    @Override
    public void run() {
        DatabaseClient.getInstance(getApplicationContext()).getAppDataBase().taskDao().delete(task);

    }
},1000);

        }
    }

标签： javaandroidandroid-studioandroid-recyclerviewandroid-room

解决方案

欢迎加入堆栈

您的接口已声明但未分配，因此当单击列表中的项目时您将抛出空指针，但在触发方法接口之前检查 null

首先在适配器OnDeleteClickListener内部添加 setter

public void setOnDeleteClickListener(OnDeleteClickListener listener){
 this.onDeleteClickListener=listener;
}

并添加当用户单击项目时从列表中删除项目的代码，因此在setData方法内部更新此代码

    view.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        if (onDeleteClickListener != null) {
            onDeleteClickListener.OnDeleteClickListener(taskList.get(position));
            //remove item from list and then notify adapter data is changed
            taskList.remove(position);
            notifyDataSetChanged();
        }
    }
});

最后到触发器onDeleteClickListener里面你AsyncTask 更新你的代码在这里

@Override
 protected void onPostExecute(List < Task > tasks) {
     super.onPostExecute(tasks);
     TaskAdapter taskAdapter = new TaskAdapter(MainActivity.this, tasks, this);
     LinearLayoutManager layoutManager = new LinearLayoutManager(MainActivity.this);
     recyclerView.setLayoutManager(layoutManager);
     recyclerView.addItemDecoration(new DividerItemDecoration(getApplicationContext(), DividerItemDecoration.VERTICAL));
     recyclerView.setAdapter(taskAdapter);

     //pass this that refer to my interface 
     taskAdapter.setOnDeleteClickListener(this);


 }

在您的 OnDelete 中，只需使用此代码在另一个线程中运行

AsyncTask.execute(new Runnable() {
    @Override
    public void run() {
        DatabaseClient.getInstance(getApplicationContext()).getAppDataBase().taskDao().delete(task);

    }
});

建议：不要命名你的变量或参数，如 String t01、String t02..etc ，选择这个变量的名称，如 String taskComment、String taskName ..etc

我希望这对你有帮助

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