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如何将数据绑定变量作为 xml 属性传递给自定义视图

[英]How to pass data binding variable as xml attribute to custom view

 原文  2019-11-05 21:43:40  4   1    android/ android-custom-view/ android-databinding/ android-architecture-components/ android-livedata

问题描述

I am trying to create a simple form layout that uses a ViewModel containing LiveData to bind to each form field so that the inputted data can persist through configuration changes and back navigation (in the case of a multi-step form).我正在尝试创建一个简单的表单布局，该布局使用包含 LiveData 的 ViewModel 绑定到每个表单字段，以便输入的数据可以通过配置更改和后退导航（在多步表单的情况下）持续存在。 Additionally, I have a custom form field view with its own layout xml to do some required processing.此外，我有一个自定义表单字段视图，它有自己的布局 xml 来做一些必要的处理。 However, I am having difficulty passing data through the form layout to bind to the custom view layout.但是，我很难通过表单布局传递数据以绑定到自定义视图布局。

Here is a simplified version of my ViewModel, Fragment, Field object and its layout:这是我的 ViewModel、Fragment、Field object 及其布局的简化版本：

class FormViewModel : ViewModel() {
    @Bindable val email = MutableLiveData<String>().apply { value = "" }
}

class FormFragment : BaseFragment() {

    private val formViewModel: FormViewModel by lazy {
        ViewModelProviders.of(requireActivity()).get(FormViewModel::class.java)
    }

    override fun onCreateView(inflater: LayoutInflater, 
                              container: ViewGroup?, 
                              savedInstanceState: Bundle?) : View? =
        (DataBindingUtil
            .inflate(inflater, R.layout.fragment_form, container, false) as FragmentFormBinding)
            .apply {
                lifecycleOwner = requireActivity()
                viewModel = formViewModel
            }
            .root
}

class Field @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0)
    : LinearLayout(context, attrs, defStyleAttr) {

    @Bindable var fieldData: MutableLiveData<String> = MutableLiveData<String>().apply { value = "" }

    init {
        val inflater = context.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
        (DataBindingUtil
            .inflate(inflater, R.layout.field, this, true) as FieldBinding)
            .apply { fieldData = this@Field.fieldData }
            .root
    }
}

field.xml字段.xml

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

    <data>
        <variable
                name="fieldData"
                type="androidx.lifecycle.MutableLiveData&lt;String>"/>
    </data>

    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">
        <com.google.android.material.textfield.TextInputLayout
                android:id="@+id/inputField"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                tools:hint="Email">

            <com.google.android.material.textfield.TextInputEditText
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:hint="Email"
                    android:text="@={ fieldData }" />

        </com.google.android.material.textfield.TextInputLayout>
    </LinearLayout>
</layout>

What I would like to do is bind the live data from the ViewModel to a form field by passing it as an attribute to an instance of my custom form field in the form xml like so:我想做的是将 ViewModel 中的实时数据绑定到表单字段，方法是将其作为属性传递给我的自定义表单字段的实例，格式为 xml，如下所示：

<?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>
        <variable name="viewModel"
                type="packageName.FormViewModel"/>
    </data>

    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            android:padding="32dp">

        <packageName.Field
                android:id="@+id/emailField"
                app:fieldData="@{ viewModel.email }"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="60dp" />

    </LinearLayout>
</layout>

However, when I try this I get the following error:但是，当我尝试此操作时，出现以下错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: packageName, PID: 27543
    java.lang.RuntimeException: Failed to call observer method
        at androidx.lifecycle.ClassesInfoCache$MethodReference.invokeCallback(ClassesInfoCache.java:226)
        at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeMethodsForEvent(ClassesInfoCache.java:194)
        at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeCallbacks(ClassesInfoCache.java:185)
        at androidx.lifecycle.ReflectiveGenericLifecycleObserver.onStateChanged(ReflectiveGenericLifecycleObserver.java:37)
        at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:361)
        at androidx.lifecycle.LifecycleRegistry.addObserver(LifecycleRegistry.java:188)
        at androidx.databinding.ViewDataBinding.setLifecycleOwner(ViewDataBinding.java:394)
        at packageName.FormFragment.onCreateView(FormFragment.kt:24)
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2669)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1321)
        at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2515)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2290)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2246)
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2143)
        at androidx.fragment.app.FragmentManager$3.run(FragmentManager.java:417)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.IllegalArgumentException: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkParameterIsNotNull, parameter <set-?>
        at packageName.Field.setFieldData(Field.kt)
        at packageName.databinding.FragmentFormBindingImpl.executeBindings(FragmentFormBindingImpl.java:127)
        at androidx.databinding.ViewDataBinding.executeBindingsInternal(ViewDataBinding.java:472)
        at androidx.databinding.ViewDataBinding.executePendingBindings(ViewDataBinding.java:444)
        at androidx.databinding.ViewDataBinding$OnStartListener.onStart(ViewDataBinding.java:1685)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at androidx.lifecycle.ClassesInfoCache$MethodReference.invokeCallback(ClassesInfoCache.java:216)
        at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeMethodsForEvent(ClassesInfoCache.java:194) 
        at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeCallbacks(ClassesInfoCache.java:185) 
        at androidx.lifecycle.ReflectiveGenericLifecycleObserver.onStateChanged(ReflectiveGenericLifecycleObserver.java:37) 
        at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:361) 
        at androidx.lifecycle.LifecycleRegistry.addObserver(LifecycleRegistry.java:188) 
        at androidx.databinding.ViewDataBinding.setLifecycleOwner(ViewDataBinding.java:394) 
        at packageName.FormFragment.onCreateView(FormFragment.kt:24) 
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2669) 
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1321) 
        at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2515) 
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2290) 
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2246) 
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2143) 
        at androidx.fragment.app.FragmentManager$3.run(FragmentManager.java:417) 
        at android.os.Handler.handleCallback(Handler.java:739) 
        at android.os.Handler.dispatchMessage(Handler.java:95) 
        at android.os.Looper.loop(Looper.java:135) 
        at android.app.ActivityThread.main(ActivityThread.java:5221) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:372) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 

As an alternative this can easily be achieved by including the field layout instead like the following but in this case I cannot do any of the setup I would like to do in the Field object作为替代方案，这可以通过包含字段布局而不是如下所示轻松实现，但在这种情况下，我无法在字段 object 中进行任何我想做的设置

<?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>
        <variable name="viewModel"
                type="packageName.FormViewModel"/>
    </data>

    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            android:padding="32dp">

        <include
                layout="@layout/field"
                android:id="@+id/emailField"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:fieldData="@{ viewModel.email }" />
    </LinearLayout>
</layout>

I'm guessing has to do with the order in which the xml is inflated and data binding variable generated but I am having difficulty debugging我猜想与 xml 的膨胀顺序和生成数据绑定变量的顺序有关，但我很难调试

EDIT: I just noticed I am not setting the lifecycle owner in the Field data binding but the issue arises even if I am not inflating the layout in the Field class编辑：我只是注意到我没有在字段数据绑定中设置生命周期所有者，但是即使我没有在字段 class 中膨胀布局，也会出现问题

1 个解决方案

解决方案1
 2 已采纳  2019-11-06 00:51:14

Try using @BindingAdapter("...") instead of the @Bindable annotation.尝试使用@BindingAdapter("...")而不是@Bindable注释。

I made a sample repo that reflects and solves your problem, maybe have a look.我制作了一个示例 repo，它反映并解决了您的问题，也许看看。

https://github.com/phamtdat/BindingAdapterSample https://github.com/phamtdat/BindingAdapterSample

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