Enable arithmetic operations in your layout xmls

There have been so many instances while creating views using xmls, I’ve wished I could perform arithmetic operations of dimensions. Thanks to DataBinding you can do this now. In this blog I will explain

1. How to enable databinding in your android project.
2. Enable data binding in your layout file.
3. Writing binding adapters.

To enable data binding feature in your android project add the following lines to your build.gradle

dataBinding {
    enabled = true
}

Next to make your layout file work with data binding libraries. Surround your layout file with <layout> tag as shown in the below code snippet

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

<!-- UI layout's root element -->
<RelativeLayout
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recylerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginBottom="@dimen/dimen1 + @dimen/dimen2"
     />
</RelativeLayout>
</layout>

Next step is to write BindingAdapters. Below is one such example.

@BindingAdapter("android:layout_marginBottom")
public static void setMarginBottom(View view, float bottomMargin) {
 ViewGroup.MarginLayoutParams layoutParams = ViewGroup.MarginLayoutParams) view.getLayoutParams();
 layoutParams.setMargins(layoutParams.leftMargin, layoutParams.topMargin,
 layoutParams.rightMargin,(int) bottomMargin);
 view.setLayoutParams(layoutParams);
}

You can have your BindingAdapters in your class where you inflate your views or you can create a separate class where you have all your BindingAdapters in one place. The method name can be anything you want but the parameters have to be:

public static void yourMethodName(View view, float bottomMargin)

With the above steps you make it possible to have expressions in your layout xml files. Databinding is a powerful library. In this blog I have given one area in which you can apply data binding. For more information regarding databinding refer to android developers guide.

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