Android ViewBinding with CustomView

Question

I'd like to use try out the ViewBinding with custom view, for example:

MainActivity <=> layout_main.xml
MyCustomView <=> layout_my_custom_view.xml

layout_main.xml

<FrameLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.example.myapplication.MyCustomView
            android:id="@+id/custom_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
</FrameLayout>

layout_my_custom_view.xml

<LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <TextView
            android:id="@+id/line1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Line1" />

        <View
            android:id="@+id/divider"
            android:layout_width="match_parent"
            android:layout_height="2dp"
            android:background="#2389bb" />

        <TextView
            android:id="@+id/line2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Line2" />
</LinearLayout>

MainActivity

class MainActivity : AppCompatActivity() {

    private lateinit var binding: LayoutMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = LayoutMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        binding.customView.line1.text = "Hello"
        binding.customView.line2.text = "World"
    }
}

In my MainActivity, I can use the binding to find MyCustomView but I can't further find @id/line1 and @id/line2 in MyCustomView. In this case, is it possible to use ViewBinding only or do I have to use findViewById or Kotlin synthetic ??

Thanks in advance.

what's problem? you can use **kotlin synthetic** as `custom_view.line1` — Ethan Choi, Feb 27 '20 at 02:19
@EthanChoi Thanks. I know I can use kotlin synthetics or findViewById, but I want to know is it possible to use ViewBinding only. — Z.J Hung, Feb 27 '20 at 02:27

score 41 · Accepted Answer · answered Feb 27 '20 at 03:15

41

ViewDataBinding.inflate doesn't generate of child view accessor inside custom view.

thus, you can't touch line1(TextView) via only use ViewDataBinding.

If you don't want using findViewById or kotlin synthetic, MyCustomView also needs to apply ViewDataBinding. try as below.

CustomView

class MyCustomView @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : LinearLayout(context, attrs, defStyleAttr) {
    private val binding =
        CustomLayoutBinding.inflate(LayoutInflater.from(context), this, true)

    val line1
        get() = binding.line1

    val line2
        get() = binding.line2
}

MainActivity

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    val binding = ActivityMainBinding.inflate(LayoutInflater.from(this))
    setContentView(binding.root)

    with(binding.customView) {
        line1.text = "Hello"
        line2.text = "World"
    }
}

answered Feb 27 '20 at 03:15

Ethan Choi

2,339
18
28

Great. So in your opinion, which one do you suggest? Apply ViewBinding in MyCustomView and expose child views as properties? Or use `findViewById` or `kotlin synthetic`? – Z.J Hung Feb 27 '20 at 03:28
@Z.JHung That depends on your needs. If exist `MyCustomViewModel` for `MyCustomView`, `ViewDataBinding` is more effective, otherwise it's better to use `kotlin synthetic`. – Ethan Choi Feb 27 '20 at 05:12
1

could you also make the val binding in CustomView public, and then access line1 or line2 in MainActivity in the following way: binding.customView.binding.line1? Or is it a bad practice to do it this way? – Praveen P. Nov 29 '20 at 15:23
Can someone confirm or correct my assumption here: attachToRoot = true, when using as view inside a normal layout/view (e.g. fragment) and since we will set it to attachToRoot = false inside the onCreateViewHolder within an Adapter (if we use it as itemView) it does not matter if we have set it to true here – Javatar Jun 23 '21 at 13:45

Igor Fridman · Answer 2 · 2021-07-21T05:58:51.897

5

Another approach is to return the CustomView binding object.

class CustomView constructor(context: Context, attrs: AttributeSet?) : 
    ConstraintLayout(context, attrs){
                
        private val _binding: CustomViewBinding = CustomViewBinding.inflate(
                        LayoutInflater.from(context), this, true)
                
                val binding get() = _binding    
        }

And then in your Activity or Fragment:

binding.customView.binding.line1?.text = "Hello"
binding.customView.binding.line2?.text = "World"

edited Jul 21 '21 at 05:58

answered Jul 19 '21 at 15:40

Igor Fridman

1,267
1
16
30

just remove private from val _binding – Shwarz Andrei Aug 07 '21 at 23:12
1

@ShwarzAndrei _binding is private the binding is the getter of it. – Igor Fridman Aug 08 '21 at 06:24
This is cleaner and for those who want to access all the child views of their Custom View in their fragments without making their Custom View binding object public – Siddhivinayak Oct 28 '21 at 09:35
Preferring this. It is less effort when making changes to the custom view. – falconforce Aug 31 '23 at 09:13

score 0 · Answer 3 · answered Feb 27 '20 at 02:45

0

I believe you can have setter in your custom view. Since ViewBinding generates binding class for your main layout, it should return you the CustomView class. Thus, you can use the setter you just wrote for changing the texts.

answered Feb 27 '20 at 02:45

Arda Kucukoz

1
1

Sounds like I have to make MyCustomView a more wrapped class. I have to add `setLine1Text()`, `setLine2Text()`, `setLine1Visibility()`, `setLine2Visibility()`,... etc. I might give it a try when custom view is not holding too many sub views. – Z.J Hung Feb 27 '20 at 03:10
Or, for second thought, you can even use `attrs.xml` file to set the attributes. That way, it would be more like a view instead of wrapper class. – Arda Kucukoz Feb 27 '20 at 03:30

Android ViewBinding with CustomView

3 Answers3

CustomView

MainActivity

Linked