Data-Binding fails with “couldn't make a guess”

问题

Since the update to Android Studio 3.2.0 I face the following issue:

Execution failed for task ':mobile:dataBindingGenBaseClassesDebug'.

> couldn't make a guess for com.ACME.database.model.Order

also seen this answer, which hints for that "package-names must start with a lower-case letter".

... it seems alike, as if this variable assignment would be the cause:

<data class=".databinding.OrderFragmentBinding">
    <variable name="order" type="com.ACME.database.model.Order"/>
    ...
</data>

found: New data binding compiler for binding classes, which does not explain the change in behavior.

Q: are such assignments also affected by that naming convention? I mean, is there any chance (beside changing the uppercase package-name) to make that data-binding v2 "guess" work out?

回答1:

these settings in the gradle.properties do enable the androidx data-binding compiler:

android.databinding.enableV2 = false
android.enableExperimentalFeatureDatabinding = true

one can see that by the fetched package:

Download https://dl.google.com/dl/android/maven2/androidx/databinding/databinding-compiler/3.2.0/databinding-compiler-3.2.0.pom
Download https://dl.google.com/dl/android/maven2/androidx/databinding/databinding-compiler/3.2.0/databinding-compiler-3.2.0.jar

and it complains:

WARNING: The option setting 'android.databinding.enableV2=false' is experimental and unsupported.
The current default is 'true'

WARNING: The option setting 'android.enableExperimentalFeatureDatabinding=true' is experimental and unsupported.
The current default is 'false'

most likely androidx.fragment.app.Fragment instead of android.support.v4.app.Fragment would be required, in order to data-bind a Fragment with the default v2 data-binding compiler. this is also just a temporary solution - but still better than to revert to the v1 data-binding compiler.

Update:

Since com.android.tools.build:gradle:3.5.0 the above workaround does not work anymore; One has to refactor the XML files. It works best when not adding any class="" attribute into the <data /> tag - and also adding this tag into any existing <layout> tag. Duplicate id on data-bound <include> tags may also prevent the generation (the id has to be set on the <include> tag, not in the included layout).

回答2:

Same thing happening to me after updating to 3.2 (working application before the migration, and no code change)... then this "guess" issue even though I do have lowercase in the first letters of the package name!

<data>
   ...
   <variable name="rule" type="com.gta.viewmodels.vmRule"/>
   ...
</data>

So I "guess" your issue will still remain even after you update the package name (which is best practice anyways, given issues appear every single time I upgrade Android Studio!).

Anyway, I solved by downgrading the v2 databinding in gradle.properties (you'll get an "unsupported" warning, but just ignore it):

android.databinding.enableV2=false

Looks like the Android Studio PG hasn't tested that well this assertion (here):

Data Binding V2 is now enabled by default and is compatible with V1.

回答3:

Its because of you class name or package name which use databinding. These class( which use databinding) have to start with capital word and packages start with lowercase.