[移动开发]Kotlin实现监听数据变化

数据监听类DataListenerController：

class DataListenerController<T> {

    private val blocks = arrayListOf<(T?) -> Unit>()

    var value: T? = null
        set(value: T?) {
            if (Looper.getMainLooper().thread == Thread.currentThread()) {
                blocks.forEach { it.invoke(value) }
            } else {
                App.handler.post {
                    blocks.forEach { it.invoke(value) }
                }
            }

        }

    fun addListener(block: (T?) -> Unit) {
        if (!blocks.contains(block)) {
            blocks.add(block)
        }
    }

}

App类：

class App : Application() {

    companion object {
        val handler = Handler()
    }

    override fun onCreate() {
        super.onCreate()
        Utils.init(this)
    }
}

以下是MVP模式下的Presenter：

class MusicsPresenter {

    enum class MusicsLoadState {
        LOADING, EMPTY, SUCCESS, ERROR
    }

    private val musicsMode by lazy {
        MusicsModel()
    }

    val musicList = DataListenerController<List<Music>>()
    val loadState = DataListenerController<MusicsLoadState>()

    private val page = 1
    private val size = 20


    fun getMusic() {
        loadState.value = MusicsLoadState.LOADING
        musicsMode.loadMusicsByPage(page, size, object : MusicsModel.OnMusicLoadResult {
            override fun onSuccess(result: List<Music>) {
                musicList.value = result
                loadState.value = if (result.isEmpty()) {
                    MusicsLoadState.EMPTY
                } else {
                    MusicsLoadState.SUCCESS
                }
            }

            override fun onError(msg: String, code: Int) {
                loadState.value = MusicsLoadState.ERROR
                println("error...$msg...$code")
            }

        })
    }
}

View层：

class MusicsActivity : AppCompatActivity() {

    private val musicsPresenter by lazy {
        MusicsPresenter()
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_musics)

        initDataListener()

        initListener()
    }

    private fun initDataListener() {
        musicsPresenter.musicList.addListener {
            println(Thread.currentThread().name)
            println("长度: ${it?.size}")
            musicCountText?.text = "长度: ${it?.size}"
        }
        musicsPresenter.loadState.addListener {
            println("状态: $it")
        }

    }

    private fun initListener() {
        getMusicsBtn.setOnClickListener {
            musicsPresenter.getMusic()
        }
    }

}

Model层：

class MusicsModel {
    fun loadMusicsByPage(page: Int, size: Int, callback: OnMusicLoadResult) {
        val result = arrayListOf<Music>()
        Thread {
            for (i in (0..size)) {
                result.add(
                    Music("音乐的名称: $i", "封面: $i", "url: $i")
                )
            }
            callback.onSuccess(result)
        }.start()


    }

    interface OnMusicLoadResult {
        fun onSuccess(result: List<Music>)
        fun onError(msg: String, code: Int)
    }
}