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Vincent Tsen
Vincent Tsen

Posted on • Updated on • Originally published at vtsen.hashnode.dev

2 Ways to Implement Binding Adapters

One way is using function parameter and another way is using extension function.

There could be more than 2 ways to implement binding adapters, but this is what I know. Let's look at what binding adapters are first.

What is Binding Adapters?

Binding adapter is used for implementing custom attribute in your layout file. For example, instead of using the defaultandroid:text attribute, you want to customize it by creating a new attribute app:customText.

Default Attribute - android:text

<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!"/>
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Custom Attribute - app:customText

<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:customText="@{`Hello World!`}"/>
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To implement custom attribute, we use binding adapters. Binding adapter is part of the data binding library. So you need to enable data binding in your build.gradle module file.

android {
    ...
    buildFeatures {
        dataBinding true
    }
}
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To implement a binding adapter, you need to annotate the function with @BindingAdapter("attribute name here") together with View class that you want to bind to. It can be done by passing the View class (e.g. TextView) as a function parameter or using the extension function.

1. Pass View as Function Parameter

I am not sure if this is a standard way (or maybe a recommended way?) but this is in the official documentation. What I learned initially is the second method below (i.e. using the extension function)

@BindingAdapter("customText")
fun setCustomText(view:TextView, item: String) {
    view.text = "My Custom String: $item"
}
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2. Use View Extension Function

@BindingAdapter("customText")
fun TextView.setCustomText(item: String) {
    text = "My Custom String: $item"
}
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Because this is an extension function, you can call it in code directly like this.

binding.textView.setCustomText("Hello World!")
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You can do that with the first method too, but the second method is more readable.

Personally

I prefer the second method, use the extension function to implement binding adapter. It reflects the actual intention, which is to extend theTextView functionality.


Originally published at https://vtsen.hashnode.dev.

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