数据绑定 + LiveData 不适用于复杂的嵌套对象

Question

我在 LiveData 和数据绑定库中遇到了一些意外行为。 我已经在这个答案https://stackoverflow.com/a/48194074/13321296 中实现了 CustomLiveData，所以我可以在父类中调用 notifyChange() 来更新 UI。

我有父对象（为了简洁省略了一些方法）：

class Day(val tasks: MutableList<RunningTask>,
          state: DayState = DayState.WAITING,
          var dayStartTime: Long = 0L,
          currentTaskPos: Int = 0): BaseObservable() {

    var state: DayState = state
        set(value) {
            field = value
            notifyChange()
        }

    var currentTaskPos: Int = currentTaskPos
        set(value) {
            field = value
            notifyChange()
        }

    fun start() {
        dayStartTime = System.currentTimeMillis()
        state = DayState.ACTIVE
        resetTasks()
        tasks[currentTaskPos].start()

        notifyChange()
    }
}

子对象：

class RunningTask(
    startTime: Long,

    var name: String = "",
    private val originalDuration: Long = 0L,

    val sound: String
): BaseObservable() {
    var startTime: Long = startTime
        set(value) {
            field = value
            uiStartTime = convertMillisToStringFormat(value)
        }

    @Bindable
    var uiStartTime: String = convertMillisToStringFormat(startTime)
        set(value) {
            field = value
            notifyPropertyChanged(BR.uiStartTime)
        }

    var duration: Long = originalDuration
        set(value) {
            field = value
        }

    var state: State = State.WAITING

    var progress: Long = 0L
        set(value) {
            field = value
        }

    var timePaused: Long = 0L
    var timeRemain: String = convertMillisToStringFormat(duration)

    enum class State {
        WAITING, ACTIVE, COMPLETED, DISABLED
    }

    fun start() {
        state = State.ACTIVE
    }
}

问题是当我更改 Day 的 tasks 字段内的项目时，来自 item_main_screen_task.xml 的数据绑定没有更新，例如调用方法 start()，但其他字段，例如 state，确实更新正确，所以我猜问题出在其中的列表。

fragment_main_screen.xml，recyclerview 填充了 Day 类字段 tasks：

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <data>
        <import type="android.view.View"/>

        <variable
            name="viewmodel"
            type="com.sillyapps.meantime.ui.mainscreen.MainViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/colorPrimary">

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/tasks"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:layout_marginStart="16dp"
            android:layout_marginEnd="16dp"
            android:visibility="@{viewmodel.noTemplate ? View.GONE : View.VISIBLE}"
            app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
            app:layout_constraintBottom_toTopOf="@+id/play_button"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/constraintLayout"
            tools:listitem="@layout/item_main_screen_task"
            tools:visibility="visible" />

    </androidx.constraintlayout.widget.ConstraintLayout>

</layout>

item_main_screen_task，taskState 属性基本上就是 BindingAdapter，它根据 Day 的 state 枚举设置背景可绘制对象：

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <data>
        <variable
            name="task"
            type="com.sillyapps.meantime.data.RunningTask" />

        <variable
            name="taskAdapterPosition"
            type="Integer" />

        <variable
            name="clickListener"
            type="com.sillyapps.meantime.ui.ItemClickListener" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        app:taskState="@{task.state}"

        android:onClick="@{() -> clickListener.onClickItem(taskAdapterPosition)}">

        <TextView
            android:id="@+id/time"
            style="@style/TimeItemStyle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"

            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginBottom="8dp"
            android:text="@{task.uiStartTime}"

            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toStartOf="@+id/enter_name"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            tools:text="17:00" />

        <TextView
            android:id="@+id/enter_name"
            android:layout_width="0dp"
            android:layout_height="wrap_content"

            android:layout_marginStart="8dp"
            android:layout_marginEnd="8dp"

            android:text="@{task.name}"
            app:layout_constraintBottom_toBottomOf="@+id/time"
            app:layout_constraintEnd_toStartOf="@+id/progress"
            app:layout_constraintStart_toEndOf="@+id/time"
            app:layout_constraintTop_toTopOf="@+id/time"
            tools:text="Свободное время" />

        <TextView
            android:id="@+id/progress"
            style="@style/TimeItemStyle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"

            android:layout_marginEnd="8dp"

            android:text="@{task.timeRemain}"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toEndOf="@+id/enter_name"
            app:layout_constraintTop_toTopOf="@+id/time"
            tools:text="01:00" />

    </androidx.constraintlayout.widget.ConstraintLayout>

</layout>

提前致谢。

Answer 1

原来解决方案非常简单，但有点出乎意料

子类应该扩展 BaseObservable，并在每个数据绑定字段的设置器上调用 notifyChange()，类似这样：

class RunningTask(
    startTime: Long,

    var name: String = "",
    private val originalDuration: Long = 0L,

    val sound: String
): BaseObservable() {
    var startTime: Long = startTime
        set(value) {
            field = value
            uiStartTime = convertMillisToStringFormat(value)
        }

    @Bindable
    var uiStartTime: String = convertMillisToStringFormat(startTime)
        set(value) {
            field = value
            notifyPropertyChanged(BR.uiStartTime)
        }

    var state: State = State.WAITING
        set(value) {
             field = value
             notifyChange()
        }
    
    ...
}

在提出问题之前，我似乎已经在 uiStartTime 中实现了这一点，但我只是不知道它起作用的确切原因