Any significant bug or issues with Android Databinding Library? [closed]

Question

Can anyone who uses android databinding library (com.android.databinding:dataBinder) comment about this beta library? In android developer site says "It might contain bugs, and it might not work for your use case, so use it at your own risk. " , so any issues or significant bug or bugs about it ?

Answer 1

I've been playing around with the databinding library for the past couple of weeks and it is surprisingly robust considering it is the very first version.

The only bug I have found so far has a workaround. I'll explain it below.

When using an <include> tag in your databinding layout file (a layout file which now uses the <layout> tag as the root), the generated code creates a binding for the <include> tag's parent ViewGroup.

When inflating the view using the DataBindingUtil, the application will crash with a when it tries to resolve the ViewGroup. There appears to be a different behaviour between the code generator and the runtime binding logic.

Problem Example

Here is an example layout with the problem mentioned above.

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

    <data>
    </data>

    <RelativeLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">

        <!-- This include causes no issues -->
        <include
            layout="@layout/view_content"/>

        <ScrollView
            android:layout_width="fill_parent"
            android:layout_height="fill_parent">

            <!-- This include however causes the data binding to crash on the ScrollView -->
            <include
                layout="@layout/view_content"/>

        </ScrollView>

    </RelativeLayout>
</layout>

And here is the included layout.

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

    <data>
    </data>

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Test"/>
</layout>

When attempting to use DataBindingUtil.setContentView the following crash occurs.

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ScrollView.setTag(java.lang.Object)' on a null object reference

Solution (Workaround)

The temporary workaround I found is to bind a dummy value to the <include> tag's parent ViewGroup. This allows the databinder to find the ViewGroup at runtime, avoiding the crash.

Here is an example of the fix in action:

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

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

    <RelativeLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">

        <!-- This include causes no issues -->
        <include
            layout="@layout/view_content"/>

        <ScrollView
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            bind:visibility="@{viewModel.dummyVisibility}">

            <!-- This include will not cause a problem now that the ScrollView has a value being bound -->
            <include
                layout="@layout/view_content"/>

        </ScrollView>

    </RelativeLayout>
</layout>

And here is the very basic view model:

package com.example;

import android.databinding.BaseObservable;
import android.databinding.Bindable;
import android.view.View;

public class ViewModel extends BaseObservable {
    @Bindable
    public int getDummyVisibility() {
        // TODO: This is a work around. Currently data binding crashes on certain views if they don't have binding.
        return View.VISIBLE;
    }
}

Hopefully this is fixed in future and this workaround won't be required!

Edit

I found another issue regarding custom binding adapters which I have raised at https://code.google.com/p/android-developer-preview/issues/detail?id=2421