Room+ViewModel+AsyncListDiffer【android JetPack】

 架构图如上所示：Dao层操作数据库，dataBase 实例 需要基础 RoomDataBase 执行一下 数据库的一下操作，viewModel 层 提供dataBase

使用viewmodel层提供的database 去修改操作视图，Adapter 加载结合:AsyncListDiffer

开发步骤：

1.按照Google developer开发文档将Room 接入到项目中：https://developer.android.com/training/data-storage/room

主要组件

Room 包含三个主要组件：

• 数据库类，用于保存数据库并作为应用持久性数据底层连接的主要访问点。
• 数据实体，用于表示应用的数据库中的表。
• 数据访问对象 (DAO)，提供您的应用可用于查询、更新、插入和删除数据库中的数据的方法。

数据库类为应用提供与该数据库关联的 DAO 的实例。反过来，应用可以使用 DAO 从数据库中检索数据，作为关联的数据实体对象的实例。此外，应用还可以使用定义的数据实体更新相应表中的行，或者创建新行供插入。

 

plugins {
    id 'com.android.application'
    id 'org.jetbrains.kotlin.android'
    id 'kotlin-kapt'
}

  implementation("androidx.room:room-runtime:2.4.3")
    annotationProcessor("androidx.room:room-compiler:2.4.3")
    kapt("androidx.room:room-compiler:2.4.3")

2.定义数据实体

@Entity
data class User(
 
    @PrimaryKey
    var uid: Int,
 
    @ColumnInfo(name = "first_name")
    var firstName: String?,
 
    @ColumnInfo(name = "last_name")
    var lastName: String?
) {
 
    override fun equals(any: Any?): Boolean {
        if (any == null) {
            return false
        }
        val other: User = any as User
        return ((uid == other.uid && (firstName == other.firstName) && (lastName == other.lastName)))
    }
}

3.数据访问对象Dao:

@Dao
interface UserDao {
 
    @Query("SELECT * FROM user")
    fun getAll(): LiveData>?
 
    @Query("SELECT * FROM user")
    fun getAll2(): MutableList?
 
    @Query("SELECT * FROM user WHERE uid IN (:userIds)")
    fun loadAllByIds(userIds: IntArray): List
 
    @Query("SELECT * FROM user WHERE first_name LIKE :first AND " + "last_name LIKE :last LIMIT 1")
    fun findByName(first: String, last: String): User
 
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertOneUser(users: User)
 
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertUserList(list: List<User>)
 
    @Delete
    fun delete(user: User)
 
    @Query("SELECT * FROM user ORDER BY last_name ASC")
    fun usersByLastName(): LiveData>?
 
}

注意数据访问对象Dao在插入的时候注意添加下：onConflict = OnConflictStrategy.REPLACE 意思是插入或者更新：insert or update

4.定义数据库：

 AppDatabase 定义数据库配置，并作为应用对持久性数据的主要访问点。数据库类必须满足以下条件：

• 该类必须带有 @Database 注解，该注解包含列出所有与数据库关联的数据实体的 entities 数组。
• 该类必须是一个抽象类，用于扩展 RoomDatabase。
• 对于与数据库关联的每个 DAO 类，数据库类必须定义一个具有零参数的抽象方法，并返回 DAO 类的实例。

@Database(entities = [User::class], version = 1, exportSchema = false)
abstract class AppDatabase : RoomDatabase() {
 
    abstract fun userDao(): UserDao
 
    companion object {
        @Volatile
        private var INSTANCE: AppDatabase? = null
 
        fun getInstance(): AppDatabase {
            synchronized(this) {
                var instance = INSTANCE
                if (instance == null) {
                    instance = Room.databaseBuilder(MyApplication.instance(), AppDatabase::class.java, "my-database-name")
                        .allowMainThreadQueries()
                        .build()
                    INSTANCE = instance
                }
                return instance
            }
        }
    }
}

这里定义了一个AppDatabase单例，可以在全局中时候 AppDatabase实例

5.定义：ViewModel

class MyViewModel : ViewModel() {
 
    fun getUsersList(): LiveData>? {
        return AppDatabase.getInstance().userDao().getAll()
    }
}

6.Activity中添加 viewModel的：observe：

viewModel.getUsersList()?.observe(this) {
            //获取到db 的数据后，开始显示到View上
        }

7.创建Adapter ，这里的Adapter 结合了：AsyncListDiffer：https://developer.android.com/reference/androidx/recyclerview/widget/AsyncListDiffer

public class UserAdapter extends RecyclerView.Adapter {
 
    private final AsyncListDiffer mDiffer = new AsyncListDiffer(this, DIFF_CALLBACK);
 
    @Override
    public int getItemCount() {
        int size = mDiffer.getCurrentList().size();
        return size;
    }
 
    public void submitList(List list) {
        mDiffer.submitList(list);
    }
 
    @NonNull
    @Override
    public UserViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType) {
        return new UserViewHolder(LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.item_user_adapter, viewGroup, false));
    }
 
    @Override
    public void onBindViewHolder(UserViewHolder holder, int position) {
        User user = mDiffer.getCurrentList().get(position);
        holder.bindView(user, position);
    }
 
    public class UserViewHolder extends RecyclerView.ViewHolder {
 
        TextView mIdView;
        TextView mFirstNameView;
        TextView mLastNameView;
 
        public UserViewHolder(@NonNull View itemView) {
            super(itemView);
            mIdView = itemView.findViewById(R.id.tv_id);
            mFirstNameView = itemView.findViewById(R.id.tv_first_name);
            mLastNameView = itemView.findViewById(R.id.tv_last_name);
        }
 
        public void bindView(User user, int position) {
            mIdView.setText("Id：" + user.getUid());
            mFirstNameView.setText(user.getFirstName());
            mLastNameView.setText(user.getLastName());
        }
    }
 
 
    public static final DiffUtil.ItemCallback DIFF_CALLBACK = new DiffUtil.ItemCallback() {
        @Override
        public boolean areItemsTheSame(
                @NonNull User oldUser, @NonNull User newUser) {
            // User properties may have changed if reloaded from the DB, but ID is fixed
            return oldUser.getUid() == newUser.getUid();
        }
 
        @Override
        public boolean areContentsTheSame(@NonNull User oldUser, @NonNull User newUser) {
            // NOTE: if you use equals, your object must properly override Object#equals()
            // Incorrectly returning false here will result in too many animations.
            return oldUser.equals(newUser);
        }
    };
}

8.接下来就要实现数据的增删改查，同步显示在View上了：

插入数据：insert 

   mBinding.btnAddView.setOnClickListener {
            mCoroutineScope.launch {
                val localUserList = AppDatabase.getInstance().userDao().getAll2()
                val count = localUserList?.size ?: 0
                val targetCount = count + 1
                val user = User(targetCount, "FirstName:" + targetCount, "LastName:" + targetCount)
                AppDatabase.getInstance().userDao().insertOneUser(user)
            }
        }

更新数据：update

  mBinding.btnEditView.setOnClickListener {
            mCoroutineScope.launch {
                val localUserList = AppDatabase.getInstance().userDao().getAll2()
                if (localUserList?.isNullOrEmpty() == true) {
                    return@launch
                }
                localUserList?.forEach {
                    it.firstName = it.firstName + "A"
                    it.lastName = it.lastName + "B"
                }
 
                localUserList?.let {
                    AppDatabase.getInstance().userDao().insertUserList(it)
                }
            }
        }

删除数据：delete:

 mBinding.btnDeleteView.setOnClickListener {
            mCoroutineScope.launch {
                val localUserList = AppDatabase.getInstance().userDao().getAll2()
                localUserList?.let {
                    val user = it?.get(it.size - 1)
                    if (user != null) {
                        AppDatabase.getInstance().userDao().delete(user)
                    }
                }
            }
        }

到目前为止就已经实现了：数据库的增删改查，同步显示到View 上：这样Room，ViewModel， AsyncListDiffer 结合在了一起

Demo地址：GitHub - JasonZhangHG/DiffUtilDemo: Room DB + ViewModel + AsyncListDiffer