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). Additionally, I have a custom form field view with its own layout xml to do some required processing. However, I am having difficulty passing data through the form layout to bind to the custom view layout.
Here is a simplified version of my ViewModel, Fragment, Field object and its layout:
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 = [email protected] }
.root
}
}
field.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<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:
<?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:
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
<?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
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
Try using @BindingAdapter("...") instead of the @Bindable annotation.
I made a sample repo that reflects and solves your problem, maybe have a look.