Android data binding is not working with attributes

Question

I'm trying to use databinding with custom views (a possible usage George Mount showed here).

One can't imagine building compound views without <merge> tag. However, in this situation databinding fails:

MyCompoundView class:

public class MyCompoundView extends RelativeLayout {

MyCompoundViewBinding binding;

public MyCompoundView (Context context, AttributeSet attrs) {
    super(context, attrs);
    init(context);
}

private void init(Context context){
    LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    binding = MyCompoundViewBinding.inflate(inflater, this, true);
}

my_compound_view.xml: by app:isGone="@{!data.isViewVisible}" i hoped to control the visibility of the whole compound view

<?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="data" type="com.example.MyViewModel"/>
    </data>

    <merge
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:isGone="@{!data.isViewVisible}">

        <ImageView
            android:id="@+id/image_image"
            android:layout_width="60dp"
            android:layout_height="60dp"
            app:imageUrl="@{data.imagePhotoUrl}"/>

         <!-- tons of other views-->

    </merge>

</layout>

The compiler errors:

Error:(13) No resource identifier found for attribute 'isGone' in package 'com.example'
Error:(17, 21) No resource type specified (at 'isGone' with value '@{!data.isViewVisible}').

I have all needed @BindingAdapter methods. Now I inherit the view from FrameLayout and use <RelativeLayout> instead of <merge> - and it works. But I have extra nested layout.

Question: merge attrs are ignored. Is there any way to workaround that?

Android Studio 1.5.1 stable

Gradle plugin com.android.tools.build:gradle:1.5.0

@Rakeeb Rajbhandari, yes, databinding does work ok with `` tag. However, this will not solve the problem of extra viewgroup while inflating custom view. — Dmitry Gryazin, Feb 25 '16 at 14:23
Please have a look at my question. I'm using include tag and inner class. https://stackoverflow.com/q/45143721/5214893 — eC Droid, Jul 20 '17 at 13:26

George Mount · Accepted Answer · 2017-04-11T14:15:03.073

There is no merge object after inflation, so there is nothing to assign values to with a merge tag. I can't think of any binding tag that will work on merge.

You can assign the tag to the root element and use the BindingAdapter to do what you want.

<layout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    >

    <data>
        <variable name="data" type="com.example.MyViewModel"/>
    </data>

    <merge
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <ImageView
            app:isGone="@{!data.isViewVisible}"
            android:id="@+id/image_image"
            android:layout_width="60dp"
            android:layout_height="60dp"
            app:imageUrl="@{data.imagePhotoUrl}"/>
         <!-- tons of other views-->
    </merge>
</layout>

If you want to do something with the Binding class itself, you can use the DataBindingUtil to find the object from the View.

@BindingAdapter("isGone")
public static void setGone(View view, boolean isGone) {
    ViewDataBinding binding = DataBindingUtil.findBinding(view);
    //... do what you want with the binding.
}

Exactly Android developers mentioned about it in [documentation](https://developer.android.com/topic/libraries/data-binding/index.html#layout_details) — MrOnyszko, Aug 23 '16 at 21:00
Could you elaborate your advice with some code? Thank you :) — DarkLeafyGreen, Apr 11 '17 at 07:36
Hello, I can't get the merge tag to work. It shows the error `Element merge is not allowed here`. See: https://pastebin.com/QhQKYN71 — Thomas Vos, Jun 03 '17 at 14:57
Here, `merge is not allowed here` is just a warning but it's [a known bug](https://issuetracker.google.com/issues/37150098) — Giszmo, Oct 10 '18 at 16:10

user158 · Answer 2 · 2019-11-04T15:15:57.943

Actually you can use <merge> tag inside <include> and do data binding.

Ex:

incl_button.xml

<layout>
    <merge xmlns:android="http://schemas.android.com/apk/res/android">

        <Button android:id="btn"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:text="Click"
         />

    </merge>
</layout>

fragment_example.xml

<layout xmlns:android="http://schemas.android.com/apk/res/android">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <include
            layout="@layout/incl_button"
            android:id="@+id/layout_btn" />

    </LinearLayout>
</layout>

ExampleFragment.kt

binding.layoutBtn.btn.setOnClickListener{
   //...
}

Android data binding is not working with attributes

2 Answers2

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