如何使用自定义 class 类型绑定视图模型变量

Question

什么有效？

XML:

            name="viewModel"
            type="com. . . . .MyViewModel" />
...
...
...
<android.support.v7.widget.RecyclerView
            android:id="@+id/feeds_list"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="center_horizontal"
            app:items="@{viewModel.feeds}"
            />

MyViewModel class:

private String[] feeds;
...
...
public MyViewModel() {
    String[] feeds = new String[] {"foo", "bar"};
    setFeeds(feeds);
}

@Bindable
    public  String[]  getFeeds() {
        return feeds;
    }

    public void setFeeds( String[]  feeds) {
        this.feeds = feeds;
        notifyPropertyChanged(BR.feeds);
    }

我的活动：

    @BindingAdapter({"items"})
    public static void myMethod(View view, String[] feeds) {
        // Do somthing
    }

我想改变什么？

我想将 String[] 更改为 List<Feed>，但未达到 myMethod。

我的动态 class:

public class Feed {
    private String name;

    public Feed(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

目前，这个class只包含一个String成员，当然他会包含更多。

Answer 1

在视图模型中像下面这样更改

   private MutableLiveData<List<Feed>> feedListLivedata =  new MutableLiveData<>();;



 public MyViewModel() {
    //create a list of feed here
    setFeeds(feeds);
}



public void setFeeds( List<Feed>  feeds) {
        feedListLivedata .postValue(feeds);
    }

//为 feed 列表实时数据创建 getter 和 setter。

现在 xml

 app:items="@{viewModel.feedListLivedata }"

Answer 2

如果您希望将 List 绑定到 RecyclerView。

要遵循的步骤。

1- 使用 app:items 标签在 xml 文件中创建一个 RecyclerView 以设置要绑定到的项目

 <androidx.recyclerview.widget.RecyclerView
        android:layout_width="match_parent"
        android:id="@+id/recycler_view"
        android:layout_height="match_parent"
        android:scrollbars="vertical"
        app:items="@{viewmodel.items}"
        app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager" />

2- 为 RecyclerView 列表的行创建布局。项目应该有 SomeObject 作为变量。

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

    <data>

        <import type="android.widget.CompoundButton" />

        <variable
            name="task"
            type="com...data.model.Task" />

        <variable
            name="viewmodel"
            type="com...TaskListViewModel" />
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="?android:attr/listPreferredItemHeight"
        android:orientation="horizontal"
        android:onClick="@{() -> viewmodel.openTask(task.id)}">

        <CheckBox
            android:id="@+id/complete"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:onClick="@{(view) -> viewmodel.completeTask(task, ((CompoundButton)view).isChecked())}"
            android:checked="@{task.completed}" />

        <TextView
            android:id="@+id/title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:layout_marginLeft="@dimen/activity_horizontal_margin"
            android:layout_marginStart="@dimen/activity_horizontal_margin"
            android:textAppearance="@style/TextAppearance.AppCompat.Title"
            android:text="@{task.titleForList}"
            app:completedTask="@{task.completed}" />
    </LinearLayout>
</layout>

3- 使用 ListAdapter，这是新的，它自己和在工作线程上计算行差异，而不是 RecyclerView.Adapter 并将 SomeObject 和 ViewModel 绑定到此适配器。

/** * 任务列表适配器。具有对 [TaskListViewModel] 的引用以将操作发送回它。 */

class TasksAdapter(private val viewModel: TaskListViewModel) :
        ListAdapter<Task, CustomViewHolder>(TaskDiffCallback()) {

    override fun onBindViewHolder(holder: CustomViewHolder, position: Int) {
        val item = getItem(position)

        holder.bind(viewModel, item)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomViewHolder {
        return CustomViewHolder.from(parent)
    }

    class CustomViewHolder private constructor(val binding: TaskItemBinding) :
            RecyclerView.ViewHolder(binding.root) {

        fun bind(viewModel: TaskListViewModel, item: Task) {

            binding.viewmodel = viewModel
            binding.task = item
            binding.executePendingBindings()
        }

        companion object {
            fun from(parent: ViewGroup): CustomViewHolder {
                val layoutInflater = LayoutInflater.from(parent.context)
                val binding = TaskItemBinding.inflate(layoutInflater, parent, false)

                return CustomViewHolder(binding)
            }
        }
    }
}

/**
 * Callback for calculating the diff between two non-null items in a list.
 *
 * Used by ListAdapter to calculate the minimum number of changes between and old list and a new
 * list that's been passed to `submitList`.
 */
class TaskDiffCallback : DiffUtil.ItemCallback<Task>() {
    override fun areItemsTheSame(oldItem: Task, newItem: Task): Boolean {
        return oldItem.id == newItem.id
    }

    override fun areContentsTheSame(oldItem: Task, newItem: Task): Boolean {
        return oldItem == newItem
    }
}

如何使用自定义 class 类型绑定视图模型变量

How to bind a view model variable with custom class type

android

android-databinding

android-mvvm