UI ViewModel 值更改时未更新
UI not updated when ViewModel value changed
我创建了示例应用程序来演示我的问题:
一个TextView
和一个Button
,文本视图可见性绑定到viewModel.bar
我希望按钮在单击时切换 viewModel.bar
的值,并且 UI 也得到更新。
然而,这并没有发生。值已更改,但 UI 未更新。
布局文件:
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<import type="android.view.View"/>
<variable name="viewModel"
type="com.example.bindingone.MainViewModel"/>
</data>
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/text_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World"
android:visibility="@{viewModel.bar ? View.VISIBLE : View.GONE}"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<Button
android:text="Update UI"
android:onClick="clicked"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</android.support.constraint.ConstraintLayout>
</layout>
MainActivity
文件:
class MainActivity : AppCompatActivity() {
private val viewModel = MainViewModel()
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
binding = DataBindingUtil.setContentView(this, R.layout.activity_main)
binding.viewModel = viewModel
}
fun clicked(v: View) {
viewModel.bar.value = viewModel.bar.value?.not() ?: false
}
}
MainViewModel
文件:
class MainViewModel : ViewModel() {
var bar = MutableLiveData<Boolean>()
}
创建绑定后,添加此行 binding.setLifecycleOwner(this)
。
/**
* Sets the {@link LifecycleOwner} that should be used for observing changes of
* LiveData in this binding. If a {@link LiveData} is in one of the binding expressions
* and no LifecycleOwner is set, the LiveData will not be observed and updates to it
* will not be propagated to the UI.
*
* @param lifecycleOwner The LifecycleOwner that should be used for observing changes of
* LiveData in this binding.
*/
@MainThread
public void setLifecycleOwner(@Nullable LifecycleOwner lifecycleOwner)
我创建了示例应用程序来演示我的问题:
一个TextView
和一个Button
,文本视图可见性绑定到viewModel.bar
我希望按钮在单击时切换 viewModel.bar
的值,并且 UI 也得到更新。
然而,这并没有发生。值已更改,但 UI 未更新。
布局文件:
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<import type="android.view.View"/>
<variable name="viewModel"
type="com.example.bindingone.MainViewModel"/>
</data>
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/text_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World"
android:visibility="@{viewModel.bar ? View.VISIBLE : View.GONE}"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<Button
android:text="Update UI"
android:onClick="clicked"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</android.support.constraint.ConstraintLayout>
</layout>
MainActivity
文件:
class MainActivity : AppCompatActivity() {
private val viewModel = MainViewModel()
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
binding = DataBindingUtil.setContentView(this, R.layout.activity_main)
binding.viewModel = viewModel
}
fun clicked(v: View) {
viewModel.bar.value = viewModel.bar.value?.not() ?: false
}
}
MainViewModel
文件:
class MainViewModel : ViewModel() {
var bar = MutableLiveData<Boolean>()
}
创建绑定后,添加此行 binding.setLifecycleOwner(this)
。
/**
* Sets the {@link LifecycleOwner} that should be used for observing changes of
* LiveData in this binding. If a {@link LiveData} is in one of the binding expressions
* and no LifecycleOwner is set, the LiveData will not be observed and updates to it
* will not be propagated to the UI.
*
* @param lifecycleOwner The LifecycleOwner that should be used for observing changes of
* LiveData in this binding.
*/
@MainThread
public void setLifecycleOwner(@Nullable LifecycleOwner lifecycleOwner)