获取数据绑定以观察对回收器视图的实时数据的更改

提问者：小点点

获取数据绑定以观察对回收器视图的实时数据的更改

我已经困在这上面几个小时了。非常尊重能帮我解决这个问题的人。

每当我更改我的MutableLiveData时，我的视图都不会更新。

在我的锻炼应用程序中，我有一个锻炼列表：MutableLiveData

然而，由于我的数据库绑定xml实际上并没有引用MutableLiveData

选择器活动：

class SelectorActivity : AppCompatActivity() {
private lateinit var mExerciseSelectAdapter: ExerciseSelectAdapter
private lateinit var mViewModel: SelectorViewModel

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

    mViewModel = ViewModelProviders.of(this).get(SelectorViewModel::class.java)
    mExerciseSelectAdapter = ExerciseSelectAdapter(this, mViewModel)

    setupRecyclerView()
    loadExerciseList(intent.hasExtra("LOAD_FROM_DB"), resources)
}

private fun setupRecyclerView(){
    rv_select_exers.layoutManager = LinearLayoutManager(this)
    rv_select_exers.setHasFixedSize(true)
    rv_select_exers.adapter = mExerciseSelectAdapter
}

private fun loadExerciseList(loadFromDB: Boolean, resources: Resources) {
    doAsync {
           val myDBExercises = loadExersFromDB()
           mViewModel.populateExerciseListFromDB(myDBExercises)
           mExerciseSelectAdapter.notifyDataSetChanged()
        }
    }
}

}

选择视图模型：

class SelectorViewModel : ViewModel() {
    private val mExerciseList = MutableLiveData<ArrayList<ExerciseEntity>>()
    val exerciseList : LiveData<ArrayList<ExerciseEntity>>
        get() = mExerciseList

    init {
        mExerciseList.value = ArrayList()
    }

    fun populateExerciseListFromDB(myDBExercises: List<ExerciseEntity>) {
        // .... Load our exer list from DB ... //


        mExerciseList.value?.addAll(myDBExercises)
        // Use the "setValue" method to notify observers of change
        mExerciseList.value = mExerciseList.value
    }

    private fun updateRepsInExercise(exercise: ExerciseEntity, reps1: Int, reps2: Int, reps3: Int) {
        exercise.set1Reps = reps1
        exercise.set2Reps = reps2
        exercise.set3Reps = reps3

        // Force our livedata to detect a change
        // TODO: not doing anything after increment set, our view is not updating
        mExerciseList.value = mExerciseList.value
    }

    fun incrementSet(exercise: ExerciseEntity, smallIncrement: Boolean) {
            // ... Compute the new reps ... //
            updateRepsInExercise(exercise, numReps1, numReps2, numReps3)
    }
}

练习选择适配器：

类练习选择适配器（私有val mLifaycleOwner： LifaycleOwner，私有val mViewModel：SelectorViewModel）：RecycliView.Adapter（）{私有lateinit var mWorkiseList：ArrayList

init {
    // Use this to avoid blinking of list when data is changed
    setHasStableIds(true)

    // Get a reference to our viewmodel's exercise list
    if (mViewModel.exerciseList.value != null ) mExerciseList = mViewModel.exerciseList.value!!
}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ExerciseSelectViewHolder {
    val layoutInflater = LayoutInflater.from(parent.context)
    val dataBinding: ExerciseSelectBinding = DataBindingUtil.inflate(layoutInflater, R.layout.exercise_select, parent, false);
    dataBinding.setLifecycleOwner(mLifecycleOwner)
    return ExerciseSelectViewHolder(dataBinding, mLifecycleOwner, mViewModel)
}

override fun onBindViewHolder(holder: ExerciseSelectViewHolder, index: Int) {
    holder.bindExerciseSelectView(mExerciseList[index])
}

override fun getItemCount(): Int {
    return mExerciseList.size
}

// Use this to avoid blinking of list when data is changed
override fun getItemId(position: Int): Long {
    return mExerciseList[position].exerciseNum.toLong()
}

}

练习选择视图持有者：

class ExerciseSelectViewHolder(private val mDataBinding: ExerciseSelectBinding,
                               private val mLifecycleOwner: LifecycleOwner,
                               private val mViewModel: SelectorViewModel):
        RecyclerView.ViewHolder(mDataBinding.root){

    init {
        // Used to enable proper observation of LiveData
        mDataBinding.setLifecycleOwner(mLifecycleOwner)
    }

    fun bindExerciseSelectView(exerciseEntity: ExerciseEntity) {
        mDataBinding.exerciseEntity = exerciseEntity
        mDataBinding.viewModel = mViewModel
        mDataBinding.spinnerAdapter = ArrayAdapter(mLifecycleOwner as Context,
                R.layout.simple_spinner_dropdown_item,
                exerciseEntity.allProgressions)
        // Forces the bindings to run immediately
        mDataBinding.executePendingBindings()
    }
}

activity_selector. xml：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.epsilon.startbodyweight.selectorActivity.SelectorActivity">

        <android.support.v7.widget.RecyclerView
            android:id="@+id/rv_select_exers"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    </android.support.constraint.ConstraintLayout>

exercise_select. xml：

 <?xml version="1.0" encoding="utf-8"?>
    <layout>
        <data>
            <import type="android.view.View"/>
            <variable
                name="exerciseEntity"
                type="com.epsilon.startbodyweight.data.ExerciseEntity"/>
            <variable
                name="viewModel"
                type="com.epsilon.startbodyweight.selectorActivity.SelectorViewModel"/>
            <variable
                name="spinnerAdapter"
                type="android.widget.ArrayAdapter" />
        </data>
        <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
            <Spinner
                android:id="@+id/sp_sel_exer"
                //... Styling stuff
                android:spinnerMode="dropdown"
                android:adapter="@{spinnerAdapter}"
                android:selection="@{exerciseEntity.progressionNumber}"
                android:onItemSelected="@{(parent,view,position,id) -> viewModel.onItemSelectedSpinner(parent,position,exerciseEntity)}"/>
            <Button
                android:id="@+id/b_sel_increase_reps_small"
                android:layout_width="wrap_content"
                //... Styling stuff
                android:onClick="@{() -> viewModel.incrementSet(exerciseEntity, true)}"
                android:text="↑" />
            <TextView
                android:id="@+id/tv_sel_rep_1"
                // ... Styling stuff
                android:text="@{String.valueOf(exerciseEntity.set1Reps)}"
                android:visibility="@{!exerciseEntity.isTimedExercise ? View.VISIBLE : View.GONE}"/>
            <TextView
                android:id="@+id/tv_sel_rep_2"
                //... Styling stuff
                android:text="@{String.valueOf(viewModel.exerciseList)}"
                android:visibility="@{!exerciseEntity.isTimedExercise ? View.VISIBLE : View.GONE}"/>
            <TextView
                android:id="@+id/tv_sel_rep_3"
                //... Styling stuff
                android:text="@{String.valueOf(exerciseEntity.set3Reps)}"
                android:visibility="@{!exerciseEntity.isTimedExercise ? View.VISIBLE : View.GONE}"/>
        </LinearLayout>
    </layout>

我是否需要使数据绑定观察MutableLiveData的更改

编辑：我找到了一个解决方案，很简单，但不理想。仍在寻找建议。

我没有直接将这个练习实体绑定到我的数据绑定XML布局，而是绑定了元素在列表中的位置。然后在我的xml中，我使用列表和这个索引访问元素。

在exercise_select. xml中，我已经替换了

android:text="@{String.valueOf(exerciseEntity.set2Reps)}"

由

android:text="@{String.valueOf(viewModel.exerciseList[index].set2Reps)}"

这似乎说服了数据绑定最终观察到对ArrayList的修改。

我不满意，有没有更“最佳实践”的方法来做到这一点？

共1个答案

匿名用户

我不知道你是否仍然有这个问题，但是我知道数据库绑定本身不能自己更新适配器中的练习列表，因为数据库绑定不能（也不应该）访问布局xml中的适配器实例。

您应该观察活动中练习列表的变化，如果列表发生变化，请将其提交给适配器，以便它可以更新回收器视图：

class SelectorActivity : AppCompatActivity() {
// ...
private fun setupRecyclerView(){
    rv_select_exers.layoutManager = LinearLayoutManager(this)
    rv_select_exers.setHasFixedSize(true)
    rv_select_exers.adapter = mExerciseSelectAdapter
    // observe changes to the list-liveData in the viewmodel
    mViewModel.exerciseList.observe(this) { exercises ->
        mExerciseSelectAdapter.submitList(exercises)
    }
// ...
private fun loadExerciseList(loadFromDB: Boolean, resources: Resources) {
    // I would advise to switch to kotlin-coroutines and move
    // db-loading to the viewModel into an viewModelScope-block
    // so the loading is cancelled when the app/activity is left by the user
    doAsync {
           val myDBExercises = loadExersFromDB()
           // I think doAsync (from Anko?) does not do its work on the
           // UI-thread, so switch to UI-thread before populating
           mViewModel.populateExerciseListFromDB(myDBExercises)
           // this notifyDataSetChanged is not needed anymore
           // because of the observe-call above
           // mExerciseSelectAdapter.notifyDataSetChanged()
        }
    }
}
}

编辑：我刚刚注意到您扩展了RecyclerView. Adapter，而不是ListAdapter（这将是最佳实践，但您还需要在ListAdapter中使用DiffCallback），因此您没有Adapter.submitList，因此使用新的set-method更新适配器中的列表实例，然后像您已经做的那样调用Adapter.通知fyDataSetChanged（）。

还有什么可能是更新问题的一部分：你记得在初始化期间适配器中的练习列表的快照，据我所知，从适配器的角度来看，它从来没有更新过（我认为当你更新livedata-value时，它可能是也可能不是对列表的相同引用，因为livedata可能会重新初始化其内部值存储）：

init {
    // ...

    // Get a reference to our viewmodel's exercise list
    if (mViewModel.exerciseList.value != null ) mExerciseList = mViewModel.exerciseList.value!!
}

这击败了“从db加载列表并更新列表”代码。保持简单，只让观察-lambda更改列表并直接在适配器中访问mViewModel. workiseList，而不是只访问它的初始快照。

关于填充方法，您可以在从DB加载后简单地将列表设置为livedata：

    fun populateExerciseListFromDB(myDBExercises: List<ExerciseEntity>) {
        // why load again? you load the list in loadExersFromDB and pass it in
        // .... Load our exer list from DB ... //

        // simply set the new list to the mutable livedata
        // Use the "setValue" method to notify observers of change
        mExerciseList.value = myDBExercises
    }