Android Data Binding Library vs Kotlin Android Ext

问题:

I'm reading about how the MVVM architecture works and how to use Android Data Binding Library help.

In a very general way I understand that Android Data Binding creates a link between UI layer and the underlying data model that holds the information to display.

Kotlin Android Extensions are another Kotlin plugin that will allow you to recover views from Activities, Fragments and Views. The plugin will generate some extra code that will allow you to access views in the XML layout, just as if they were properties with the name of the id you used in the layout definition.

What is the difference between using Android Data Binding Library and Kotlin Android Extensions? Are they for different purposes? Do they complement each other, in what way?

Thank you for your answers.

回答1:

Both, Kotlin Android Extensions and Android Data Binding Library help to eliminate the use of findViewById.

But there are also more things that these do, that can complement one another. To elaborate, with the Android Data Binding library, you can 'set' models in your xml files, which can then directly be leveraged to set values for the views in the layout. See how a <data> tag can be used with the data binding library.

Kotlin android extensions does not provide for this. At the same time, Kotlin android extensions provides for some amazing features like @parcelize annotation to make classes parcelable with almost no boilerplate code, etc.

To conclude, while they both eliminate the use of findViewById, they have their own features too which can complement one another well.

回答2:

Kotlin Android Extensions does not stand for only view binding. It contains other features as well. But I guess you’re talking about the view binding/caching features of Kotlin Android Extensions and wonder whether we still need databinding, since we already got rid of the findViewById calls with the synthetic properties of Kotlin. That was the question I asked to myself and my conclusion is, yes, databinding is still worth using.

From official documentation:

The Data Binding Library creates an immutable field in the binding class for each view that has an ID in the layout… The library extracts the views including the IDs from the view hierarchy in a single pass. This mechanism can be faster than calling the findViewById() method for every view in the layout.

So databinding doesn’t call findViewById on views one by one. Kotlin’s synthetic classes, on the other hand, still calls findViewById on the views under the hood, but it calls it only once for each view and caches the view reference for next calls. (Here is an article about it)

Besides, databinding has more to offer than only view caching. You can use data tags for passing data to the binding implementation and declare them in your xml, instead of setting them programmatically. You can use observable fields, binding adapters and even two-way databinding. When used to its whole power, it can significantly reduce your java/kotlin code.

回答3:

I strongly disagree with the points mentioned above. maybe because I hate writing logic in XML. so both comments mention the use of <data> tags not found in Kotlin Android Extensions (KTX). with kotlin and KTX you can do better than data tag.

let's say we have

data class Person(val name:String, 
                   val phone:String,
                   val isMale:Boolean,
                   val isMarried:Boolean)

in the activity or fragment, we can do

fun updateView(data:Person){
    with(data){

     nameTextField.text = if(isMale){
                            "Mr. $name" 
                          } else {
                             if(isMarried){
                              "Mrs. $name"
                             }else{
                              "Miss $name"
                             }
                          }
     phoneTextField.text = phone
    }
 }

in data-binding, you have to do

android:text='@{person.isMale ? "Mr."+user.name: ((user.isMarried ? "Mrs. " : "Miss. ") + user.name)}'

KTX code is way cleaner than what you have to do with data binding to achieve the same result. when you need conditions to set values to view data binding gets ugly. so for me, Kotlin Android Extensions work better. I like my code clean. you can still use both the decision is yours to make.