viewBinding 使用小结

通过视图绑定功能，您可以更轻松地编写可与视图交互的代码。在模块中启用视图绑定之后，系统会为该模块中的每个 XML 布局文件生成一个绑定类。绑定类的实例包含对在相应布局中具有 ID 的所有视图的直接引用。
在大多数情况下，视图绑定会替代 findViewById。

启用

只能在 Android Studio 3.6 Canary 11 及更高版本中使用。

1
2
3
4
5
6
android {
    ...
    viewBinding {
        enabled = true
    }
}

启用后，会根据 xml 名称生成一个驼峰命名，结尾带上 Binding 的绑定类。例如：result_profile.xml，会生成 ResultProfileBinding 的绑定类，这个绑定类 getRoot 方法返回根布局，xml 中所有有 id 的 View 也能通过此类直接获取。相比于 kotlin-android-extensions，它不会空指针，并且 id 唯一。kotlin-android-extensions 直接获取对应 id 的 view 有可能导致空指针。另一点，如果我们很多 xml 里的 id 有一样的命名，会很难区分。且如果一个页面引用了 2 个 xml，这 2 个 xml 里是不能使用同样的 id 的，编译器会不知道要去找哪个 id 从而报错，而使用 viewBinding 这些便都解决了。

当然，或许某些时候，我们不需要生成绑定类，那么可以在布局根节点，添加tools:viewBindingIgnore="true"即可：

1
2
3
4
5
<LinearLayout
    ...
    tools:viewBindingIgnore="true" >
    ...
</LinearLayout>

在 Activity 中可以这样使用 viewBinding：

1
2
3
4
5
6
7
8
private lateinit var binding: ResultProfileBinding

override fun onCreate(savedInstanceState: Bundle) {
    super.onCreate(savedInstanceState)
    binding = ResultProfileBinding.inflate(layoutInflater)
    val view = binding.root
    setContentView(view)
}

封装 Base

那么基于 viewBinding 如何封装 Base 呢？写一下封装高德地图 RouteBaseMapFragment：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
abstract class RouteBaseMapFragment<VB : ViewBinding> : BaseFragment(), DefaultLocationListener {

    protected lateinit var viewBinding: VB
    protected var needLocate = false
    private lateinit var map: AMap
    private var polyline: Polyline? = null
    private var myLocationMark: MyLocationMark? = null
    private var markerList = mutableListOf<Marker>()

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = initViewBinding(inflater, container)
        initViewModel()
        initView()
        myLocationMark = MyLocationMark(map)
        return view
    }

    @Suppress("UNCHECKED_CAST")
    private fun initViewBinding(inflater: LayoutInflater, container: ViewGroup?): View {
        val type = javaClass.genericSuperclass
        val clazz = (type as ParameterizedType).actualTypeArguments[0] as Class<VB>
        val method = clazz.getMethod(
            "inflate",
            LayoutInflater::class.java,
            ViewGroup::class.java,
            Boolean::class.java
        )
        viewBinding = method.invoke(null, inflater, container, false) as VB
        return viewBinding.root
    }

    abstract fun getMap(): AMap

    open fun getMapView(): MapView? {
        return null
    }

    open fun getTextureMapView(): TextureMapView? {
        return null
    }

    open fun initViewModel() {}

    open fun initView() {
        getMapView()?.onCreate(null)
        getTextureMapView()?.onCreate(null)
        map = getMap()
        map.showBuildings(false)
        map.showIndoorMap(false)
        map.showMapText(false)
        val uiSettings = map.uiSettings
        uiSettings.isTiltGesturesEnabled = false
        uiSettings.isScaleControlsEnabled = true
        uiSettings.isGestureScaleByMapCenter = true
        uiSettings.isZoomControlsEnabled = false
        map.animateCamera(CameraUpdateFactory.zoomTo(18f))
    }

    protected fun drawRouteLine(nodeList: List<RouteNode>, animate: Boolean = false) {
        polyline?.remove()
        val latLngList: MutableList<LatLng> = ArrayList()
        nodeList.forEach {
            latLngList.add(LatLng(it.lat, it.lon).toGCJPoint())
        }
        polyline = map.addPolyline(
            PolylineOptions().addAll(latLngList).width(10f).color(Color.parseColor("#FF7D3C"))
        )
        if (animate) {
            val boundsBuilder = LatLngBounds.Builder()
            latLngList.forEach {
                boundsBuilder.include(it)
            }
            val cameraUpdate = CameraUpdateFactory.newLatLngBoundsRect(
                boundsBuilder.build(),
                50, 20, 50, 20
            )
            map.animateCamera(cameraUpdate)
        }
    }

    protected fun clearMarker() {
        markerList.forEach { it.remove() }
        markerList.clear()
    }

    protected fun drawMark(node: RouteNode) {
        val view = PointMarkView(context, null)
        view.setData(node)
        val markerOptions = MarkerOptions()
        markerOptions.anchor(0.5f, 0.8f)
        markerOptions.position(LatLng(node.lat, node.lon).toGCJPoint())
        markerOptions.icon(BitmapDescriptorFactory.fromView(view))
        markerList.add(map.addMarker(markerOptions))
    }

    private fun drawMyLocation(location: Location) {
        if (needLocate) {
            myLocationMark?.onLocationChange(location)
        }
    }

    override fun onLocationChanged(location: Location) {
        drawMyLocation(location)
    }

    override fun onResume() {
        super.onResume()
        JLocationManager.addListener(this)
        getMapView()?.onResume()
        getTextureMapView()?.onResume()
    }

    override fun onPause() {
        super.onPause()
        JLocationManager.removeListener(this)
        getMapView()?.onPause()
        getTextureMapView()?.onPause()
    }

    override fun onDestroyView() {
        super.onDestroyView()
        getMapView()?.onDestroy()
        getTextureMapView()?.onDestroy()
        myLocationMark?.onDestroy()
    }
}

viewBinding 生成绑定类对应的基类是 ViewBinding，所以以此写相应的泛型即可。

封装 Multi-Type ItemBinder

项目中使用了 Multi-Type，每实现一个 ItemBinder，都需要实现 2 个方法：onCreateViewHolder、onBindViewHolder。那么结合 ViewBinding 就可以考虑将 onCreateViewHolder 给抽掉：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
@RestrictTo(RestrictTo.Scope.LIBRARY)
abstract class ViewBindingBinder<T, VB : ViewBinding> : ItemViewBinder<T, ViewBindingHolder<VB>>(),
    WithViewBinding<VB> {

    @NonNull
    override fun onCreateViewHolder(
        @NonNull inflater: LayoutInflater,
        @NonNull parent: ViewGroup
    ): ViewBindingHolder<VB> {
        val viewBinding: VB = onCreateViewBinding(javaClass, inflater, parent)
        return ViewBindingHolder(viewBinding)
    }

}

@RestrictTo(RestrictTo.Scope.LIBRARY)
class ViewBindingHolder<T : ViewBinding?>(val viewBinding: T) :
    RecyclerView.ViewHolder(viewBinding!!.root)

@RestrictTo(RestrictTo.Scope.LIBRARY)
interface WithViewBinding<VB : ViewBinding?> {
    fun onCreateViewBinding(
        clz: Class<*>,
        inflater: LayoutInflater,
        @Nullable container: ViewGroup?
    ): VB {
        return ViewBindingCreator<VB>().onCreateView(clz, inflater, container)
    }
}

@Suppress("UNCHECKED_CAST")
@RestrictTo(RestrictTo.Scope.LIBRARY)
class ViewBindingCreator<VB : ViewBinding?> {
    fun onCreateView(clz: Class<*>, inflater: LayoutInflater, container: ViewGroup?): VB {
        return try {
            val viewBindingType = getViewBindingType(clz)
            val inflateMethod: Method = viewBindingType
                .getDeclaredMethod(
                    "inflate",
                    LayoutInflater::class.java,
                    ViewGroup::class.java,
                    Boolean::class.javaPrimitiveType
                )
            inflateMethod.invoke(null, inflater, container, false) as VB
        } catch (e: Exception) {
            throw IllegalStateException("创建ViewBinding失败", e)
        }
    }

    private fun getViewBindingType(clzParam: Class<*>): Class<*> {
        var clz = clzParam
        var genericType: Type? = clz.genericSuperclass
        while (genericType !is ParameterizedType) {
            clz = clz.superclass
            if (clz == null) {
                genericType = null
                break
            }
            genericType = clz.genericSuperclass
        }
        checkNotNull(genericType) { "找不到ViewBinding Type" }
        val actualTypeArguments: Array<Type> =
            (genericType as ParameterizedType).actualTypeArguments
        if (actualTypeArguments.isNotEmpty()) {
            for (type in actualTypeArguments) {
                if (type is Class<*>) {
                    if (ViewBinding::class.java.isAssignableFrom(type)) {
                        return type
                    }
                }
            }
        }
        throw IllegalStateException("找不到ViewBinding Type")
    }
}

看一下 2 个 Base 封装，都是用 VB : ViewBinding 通过反射来找到相应的类，手动调用 inflate 方法即可。

扫一扫，分享到微信

微信分享二维码

tag:

    缺失模块。
    1、在博客根目录（注意不是yilia根目录）执行以下命令：
    npm i hexo-generator-json-content --save

    2、在根目录_config.yml里添加配置： 

      jsonContent:
    meta: false
    pages: false
    posts:
      title: true
      date: true
      path: true
      text: true
      raw: false
      content: false
      slug: false
      updated: false
      comments: false
      link: false
      permalink: false
      excerpt: false
      categories: false
      tags: true

小小程序猿一枚<br><br>good good study<br>day day up!