Room+ViewModel+AsyncListDiffer【android JetPack】

阳光穿透心脏的1/2处 2024-04-03 07:27 79阅读 0赞

## ![8f58d6d97b1e442c8dc597c6198bd67b.jpeg][] ##

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][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][Link 1]，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][Link 2]，用于表示应用的数据库中的表。
 *  [数据访问对象 (DAO)][_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。

![08ce0d8fb4cc4bf4a554546fa9118467.jpeg][]

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<MutableList<User>>?
    
        @Query("SELECT * FROM user")
        fun getAll2(): MutableList<User>?
    
        @Query("SELECT * FROM user WHERE uid IN (:userIds)")
        fun loadAllByIds(userIds: IntArray): List<User>
    
        @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<List<User>>?
    
    }

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][Link 1] 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<MutableList<User>>? {
            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][https_developer.android.com_reference_androidx_recyclerview_widget_AsyncListDiffer]

public class UserAdapter extends RecyclerView.Adapter<UserAdapter.UserViewHolder> {
    
        private final AsyncListDiffer<User> mDiffer = new AsyncListDiffer(this, DIFF_CALLBACK);
    
        @Override
        public int getItemCount() {
            int size = mDiffer.getCurrentList().size();
            return size;
        }
    
        public void submitList(List<User> 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<User> DIFF_CALLBACK = new DiffUtil.ItemCallback<User>() {
            @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][GitHub - JasonZhangHG_DiffUtilDemo_ Room DB _ ViewModel _ AsyncListDiffer]

[8f58d6d97b1e442c8dc597c6198bd67b.jpeg]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/9cf871ed80884f84924d6f606e2e10fa.jpeg
[https_developer.android.com_training_data-storage_room]: https://developer.android.com/training/data-storage/room
[Link 1]: https://developer.android.com/reference/kotlin/androidx/room/Database
[Link 2]: https://developer.android.com/training/data-storage/room/defining-data
[_DAO]: https://developer.android.com/training/data-storage/room/accessing-data
[08ce0d8fb4cc4bf4a554546fa9118467.jpeg]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/586b5684c73d4da69c2c8661ea447df2.jpeg
[entities]: https://developer.android.com/reference/kotlin/androidx/room/Database#entities
[RoomDatabase]: https://developer.android.com/reference/kotlin/androidx/room/RoomDatabase
[https_developer.android.com_reference_androidx_recyclerview_widget_AsyncListDiffer]: https://developer.android.com/reference/androidx/recyclerview/widget/AsyncListDiffer
[GitHub - JasonZhangHG_DiffUtilDemo_ Room DB _ ViewModel _ AsyncListDiffer]: https://github.com/JasonZhangHG/DiffUtilDemo