Android Developers. Prerequisites This codelab has been designed for those with some Android development experience. What you'll do In this codelab, you'll convert this app to Data Binding: The app has a single screen that shows some static data and some observable data, meaning that when the data changes, the UI will be automatically updated. Here's a diagram: If you're not yet familiar with the ViewModel class from the Architecture Components libraries, you can check out the official documentation.
What you'll need Android Studio 3. Once the build is complete and the app is deployed to your device or emulator, the default activity opens and looks like this: This screen shows some data and lets the user click on a button to increment a counter and update a progress bar. The SimpleViewModel class exposes: First and last name Number of likes A value describing level of popularity SimpleViewModel also lets the user increment the number of likes with the onLike method.
Not only is this slow, it's not safe because it's not checked at compile time. It sets initial values in onCreate. It'd be much better to have good defaults that are set automatically It uses the android:onClick attribute in the Button element of the XML layout declaration, which is not safe either: If the onLike method is not implemented in your activity or is renamed , the app will crash at run time.
It has a lot of code. Activities and fragments tend to grow very quickly, so it's a good idea to move as much code as possible out of them. Also, code in activities and fragments is hard to test and maintain. This project already has Data Binding enabled, but when you want to use it in your own projects the first step is to enable the library in the modules that will use it: build. GONE : View. Now, let's bind some data! Let's start with some static data binding for now.
Now we need to modify the Activity so that it inflates a Data Binding layout correctly: The layout is ready, but now it's necessary to make some changes in the activity.
Because you're using a Data Binding layout, the inflation is done in a different way. In onCreate , replace: setContentView R. Now you can set the variable values: binding. You just bound data using the library. You can start removing old code: Remove the updateName method, since the new Data Binding code is now finding the IDs and setting the text values.
Remove the updateName call in onCreate. You can now run the app. You'll see that your name has replaced Ada's. Before modifying the event handling code, you can clean up the layout a bit. First, replace the two variables for a single ViewModel. This is the way to go in the majority of cases since it keeps your presentation code and state in one place.
Now, remove things you don't need from the activity: 1. Replace binding. This step will insert the binding code in the XAML. If you see the behind code of your XAML. Applications are not just about textboxes and labels it also has actions like buttons, mouse events etc. If you want to send data to the view model class using properties we need to use bindings and if you want to send actions from the view we need to use commands. All actions from the view elements are sent to the command class so the first step is to create the command class.
In other words the command class needs to house the view model class. Below is the shortened code snippet.
There are four important points to noted about the code snippet In the above command code the view model object is passed via the constructor. Now go to the properties of the button, scroll to the command property, right click on it and click create data binding. In other words the UI will not be automatically notified about the tax calculation. So we need to send some kind of notification from the object to the UI saying that tax values have changed and the UI has reload the binding values.
To enable notification in your view model class we need to do three things. All three things are pointed in the below code with comments like point 1 , point 2 and point 3. So till now we have created a simple screen with MVVM which has both properties and command implemented. We have a view whose UI input elements i. In my other account, windows 10 spotlight can show the picture, not the mountain one.
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