删除房间内数据库
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【中文标题】删除房间内数据库【英文标题】：Deleting In Room Database 【发布时间】：2020-05-20 16:57:02 【问题描述】：我正在学习房间数据库！！ 我知道如何从房间数据库中插入和检索数据到回收站视图！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
这就是为什么我也在Interface中使用delete方法并在Recycler View Adapter中添加Interface，这会回调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);
【问题讨论】：
【参考方案1】：欢迎加入栈
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，但请在触发方法接口之前检查空指针
首先在你的适配器
中为OnDeleteClickListener添加setter
public void setOnDeleteClickListener(OnDeleteClickListener listener)
this.onDeleteClickListener=listener;
并且还添加了当用户单击项目时从列表中删除项目的代码
所以在setData方法里面更新这段代码
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();
);
终于在你的AsyncTask 中触发onDeleteClickListener
在此处更新您的代码
@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：不要将变量或参数命名为 String t01,String t02..etc ,选择这个变量 jop 的名字 比如 String taskComment,String taskName ..etc
希望对你有帮助
【讨论】：
非常感谢 @PiyushJaiswal 欢迎您，如果对您有帮助，请让我的回答正确并投票 我也使用构造函数设置值 但是它是如何从房间数据库中删除的 将任务从 OnDeleteClickListener 传递给 DeleteTask以上是关于删除房间内数据库的主要内容，如果未能解决你的问题，请参考以下文章
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