DataBinding

DataBinding学习，记录下来，以便查阅

1、首先添加相应的依赖和plugin

implementation "androidx.lifecycle:lifecycle-extensions:2.2.0-rc01"

　　

apply plugin: 'kotlin-kapt'

2、在activity或者fragment中创建ViewModel实例：

private val viewModel: UserProfileViewModel by lazy {
        ViewModelProvider(this.viewModelStore, this.defaultViewModelProviderFactory).get(
            UserProfileViewModel::class.java
        )
    }

3、将activity或者fragment所对应的layout改成databinding布局

<?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"
    xmlns:tools="http://schemas.android.com/tools">
    <data>
        <variable
            name="viewmodel"
            type="com.lf.jetpacktest.UserProfileViewModel" />
    </data>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:orientation="horizontal">

            <TextView
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="Name: " />

            <TextView
                android:id="@+id/user_name"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="@{viewmodel.user.name}" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:orientation="horizontal">

            <TextView
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="Gender: " />

            <TextView
                android:id="@+id/user_gender"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="@{viewmodel.user.gender}" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:orientation="horizontal">

            <TextView
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="Age: " />

            <TextView
                android:id="@+id/user_age"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:text="@{Integer.toString(viewmodel.user.age)}" />
        </LinearLayout>

        <Button
            android:id="@+id/add"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:onClick="@{()-> viewmodel.add()}"
            android:text="vote" />

        <TextView
            android:id="@+id/count"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:gravity="center"
            android:text="@{Integer.toString(viewmodel.count)}" />

        <ProgressBar
            android:id="@+id/progress_bar"
            style="?android:attr/progressBarStyleHorizontal"
            android:layout_width="200dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="10dp"
            android:max="@{100}"
            app:hideIfZero="@{viewmodel.count}"
            app:progressScaled="@{viewmodel.count}"
            app:progressTint="@{viewmodel.count}"
            tools:progressBackgroundTint="@android:color/darker_gray" />
    </LinearLayout>
</layout>

即在最外层添加<layout></layout>布局，并将命名空间移至layout中，由代码可见，可在布局中加入相应的变量，以便于与具体的控件相绑定

4、将ViewModel与视图进行绑定

　　（1）在activity中

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val binding: UserProfileLayoutBinding =
            DataBindingUtil.setContentView(this, R.layout.user_profile_layout)
        binding.viewmodel = viewModel
        binding.lifecycleOwner = this
    }

　　（2）在fragment中

override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val binding: UserProfileLayoutBinding =
            DataBindingUtil.inflate(inflater, R.layout.user_profile_layout, container, false)
        binding.viewmodel = viewModel
        binding.lifecycleOwner = this
        return binding.root
    }

5、动态绑定数据，借助livedata

class UserProfileViewModel : ViewModel() {
    private val _user = MutableLiveData<User>(User("123", "male", 34))
    private val _count = MutableLiveData(0)

    val user: LiveData<User> = _user
    val count: LiveData<Int> = _count
    fun add() {
        _count.value = (_count.value ?: 0) + 1
        println(_count!!.value)
    }
}

6、实现定制化绑定

@BindingAdapter("app:hideIfZero")
fun hideIfZero(view: View, number: Int) {
    view.visibility = if (number == 0) View.GONE else View.VISIBLE
}

@BindingAdapter(value = ["app:progressScaled", "android:max"], requireAll = true)
fun setProgress(view: ProgressBar, count: Int, max: Int) {
    view.setProgress((count * 5 ).coerceAtMost(max))
}

@BindingAdapter("app:progressTint")
fun tintProgress(view: ProgressBar, count: Int) {
    val color = getAssociatedColor(count, view.context)
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        view.progressTintList = ColorStateList.valueOf(color)
    }
}

private fun getAssociatedColor(count: Int, cotext: Context): Int {
    return when {
        count > 9 -> ContextCompat.getColor(cotext, R.color.colorAccent)
        else -> ContextCompat.getColor(cotext, R.color.colorPrimary)
    }
}

OK, 简单的例子完成