barebones to get live data and data binding working#1
barebones to get live data and data binding working#1
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README.md
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| Architecture: MVVM | ||
| Language: Kotlin | ||
| Architectural Components: LiveData, Data Binding |
| import android.view.ViewGroup | ||
| import android.widget.EditText | ||
| import com.example.livedata.databinding.FragmentLoginBinding | ||
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| override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? { | ||
| super.onCreate(savedInstanceState) | ||
| loginViewModel = ViewModelProviders.of(this).get(LoginViewModel::class.java) | ||
| binding = DataBindingUtil.inflate(inflater, R.layout.fragment_login, container, false) |
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You can also use the autogenerated binding class to inflate if you want it to be more specific. FragmentLoginBinding.inflate(inflater)
| it.lifecycleOwner = this | ||
| it.loginViewModel = loginViewModel | ||
| return it.root | ||
| } |
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Since fragment lifecycles are a bit more complicated than activity's lifecycle (and causes issues, you can read about it here), they added a lifecycle that represents the fragment's. Use getViewLifecycleOwner() instead.
I think it'd be cleaner if you separate the field initialization and the return lines like:
return binding.apply {
lifecycleOwner = getViewLifecycleOwner()
loginViewModel = loginViewModel
}.root
But not necessary
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This does not work without having to name the private variable loginViewModel something different. apply changes scope to this so any reference to loginViewModel will imply this. loginViewModel = this.loginViewModel
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when you use let it.loginViewModel is the attribute on binding and loginViewModel is the private variable in the Fragment
| binding.run { | ||
| user?.let { | ||
| when { | ||
| it.emailAddress.isEmpty() -> setErrorOnField(emailAddress, R.string.empty_email_error) |
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Shouldn't all this logic be in view model? You can expose an error live data field that emits what kind of error to show and the fragment only knows about displaying error with the info vm emits.
| import android.view.View | ||
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| class LoginViewModel : ViewModel() { | ||
| var emailAddress = MutableLiveData<String>() |
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We don't want to expose the mutable versions of our LiveData fields to the view i.e. we don't want the view to be able to update them because that violates the direction of data flow. Use instead:
private val mutableEmailAddress = MutableLiveData<String>()
val emailAddress: LiveData<String> = mutableEmailAddress
The view can only observe the immutable reference. Only your vm can update the mutable because it is private.
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looks like russell and dz went back and forth on this IntrepidPursuits/skotlinton-android#33. Gonna go with anton's change to the BaseViewModel
| super.onCreate(savedInstanceState) | ||
| setContentView(R.layout.activity_main) | ||
| val fragment = LoginFragment() | ||
| supportFragmentManager.beginTransaction().add(R.id.container, fragment).commit() |
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probably be easier to read if you break it down in different lines
| const val PASSWORD_LENGTH = 5 | ||
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| data class User(val emailAddress: String, val password: String) { | ||
| val isEmailValid: Boolean |
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I imagine you'd have to do email validation more than just when you get the User object. Probably be more useful in a Utils class.
This if fine for now because it's only used for User class.
| android:ems="10" | ||
| android:hint="@string/e_mail_address_field_placeholder" | ||
| android:inputType="textEmailAddress" | ||
| android:text="@={LoginViewModel.EmailAddress}" |
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Is the capital letter EmailAddress a typo? your field in your view model is small letter e.
| android:ems="10" | ||
| android:hint="@string/password_field_hint" | ||
| android:inputType="textPassword" | ||
| android:text="@={LoginViewModel.Password}" |
| val emailAddress: LiveData<String> = mutableEmailAddress | ||
| val password: LiveData<String> = mutablePassword | ||
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| private var userMutableLiveData: MutableLiveData<User> = MutableLiveData() |
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| private var userMutableLiveData: MutableLiveData<User> = MutableLiveData() | ||
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| val user: MutableLiveData<User> |
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Is there a reason this isn't in the same format as the other live data fields? i.e.
private val mutableUser = MutableLiveData<User>()
val user: LiveData<User> = mutableUser
| set(value) { | ||
| (this as MutableLiveData<T>).value = value | ||
| } | ||
| } No newline at end of file |
| private fun setErrorOnField(editText: EditText, errorResource: Int) { | ||
| editText.error = getString(errorResource) | ||
| editText.requestFocus() | ||
| private fun EditText.setErrorOnField(errorType: LoginErrorType) { |
| const val PASSWORD_LENGTH = 5 | ||
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| @Bindable | ||
| sealed class LoginErrorType { |
| android:inputType="textEmailAddress" | ||
| android:text="@={LoginViewModel.email}" | ||
| android:hint="@string/username_field_placeholder" | ||
| android:text="@={LoginViewModel.username}" |
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maybe change it to lower case loginViewModel since it's a variable name.
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