如何与livedata进行数据绑定? [英] How can I do databinding with livedata?
问题描述
如何对livedata进行数据绑定?
How can I do databinding with livedata?
activity_user_detail.xml:
activity_user_detail.xml:
<data>
<variable
name="viewModel"
type="com.test.viewmodel.UserViewModel" />
</data>
<TextView
android:id="@+id/tv_amount"
android:layout_width="match_parent"
android:text="@{viewModel.age}"
....
UserViewModel.java:
UserViewModel.java:
public class UserViewModel extends ViewModel {
public LiveData<User> user;
public void getUserById(UserDao userDao, String userId){
transaction = UserDao .load(userId);
}
}
UserDao.java:
UserDao.java:
@Query("SELECT * FROM `user` WHERE id = :userId")
LiveData<User> load(String userId);
UserDetailActivity.java:
UserDetailActivity.java:
private ActivityUserDetailBinding binding;
binding = DataBindingUtil.setContentView(this, R.layout.activity_user_detail);
viewModel = ViewModelProviders.of(this).get(UserViewModel.class);
viewModel.getUserById(userDao, userId);
viewModel.user.observe(this, user -> binding.setViewModel(user)); // How to bind livedata?
我也尝试过这样做:
binding.setViewModel(viewModel);
推荐答案
该示例说明了LiveData和ObservableField的工作原理.您需要使用LiveData更改T对象和setValue()或使用ObservableField更改set(T).更改对象T的属性不会更新UI.
This is a sample to figure out how LiveData and ObservableField works. You need to change T object and setValue() with LiveData, or set(T) with ObservableField. Changing properties of object T does not update UI.
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<variable
name="viewModel"
type="com.example.tutorial3livedata_databinding2objects.UserViewModel" />
</data>
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/user_info"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text='@{viewModel.userMutableLiveData.name+ ", email " + viewModel.userMutableLiveData.email}'
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.501"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.1" />
<EditText
android:id="@+id/et_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="48dp"
android:text="@={viewModel.userMutableLiveData.name}"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.501"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/user_info" />
<EditText
android:id="@+id/et_email"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="28dp"
android:text="@={viewModel.userMutableLiveData.email}"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.501"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/et_name" />
<Button
android:id="@+id/button_change_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="32dp"
android:onClick="@{() -> viewModel.changeUserName()}"
android:text="Change Name"
app:layout_constraintEnd_toStartOf="@+id/button_change_user"
app:layout_constraintHorizontal_chainStyle="spread"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/et_email" />
<Button
android:id="@+id/button_change_user"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="@{() -> viewModel.changeUser()}"
android:text="Change User"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/button_change_name"
app:layout_constraintTop_toTopOf="@+id/button_change_name" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="56dp"
android:text="Display User"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/button_change_name" />
</android.support.constraint.ConstraintLayout>
</layout>
ViewModel
ViewModel
public class UserViewModel extends ViewModel {
public MutableLiveData<User> userMutableLiveData = new MutableLiveData<>();
private User mUser;
public UserViewModel() {
mUser = new User("User", "asd@abc.com");
userMutableLiveData.setValue(mUser);
}
public void changeUserName() {
// Both updates LiveData but does not update UI
mUser.setName("Name is Changed");
// userMutableLiveData.getValue().setName("Updated Name");
// This one Updates UI
// userMutableLiveData.setValue(userMutableLiveData.getValue());
}
public void changeUser() {
mUser = new User("New User Name", "myemail@mail.com");
// Without setting new value UI is not updated and observe is not called
userMutableLiveData.setValue(mUser);
}
}
MainActivity
MainActivity
/*
Without binding.setLifecycleOwner(this), liveData.setValue() does not update UI
liveData.setValue() updates UI
EditText changes LiveData but does not update UI
*/
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
UserViewModel userViewModel = ViewModelProviders.of(this).get(UserViewModel.class);
// LiveData should call setValue() to update UI via binding
binding.setViewModel(userViewModel);
// Required to update UI with LiveData
binding.setLifecycleOwner(this);
}
}
此代码仅供学习.
您可以从以下代码中获得结果:
Results you can get from this code:
1-使用changeUserName()更改用户名将更新LiveData的现有用户的名称，但不会更新UI.旋转设备时，UI会更新.
1- Changing user name with changeUserName() updates the name of existing User of LiveData but does not update UI. UI gets updated when you rotate the device.
2-当您更改LiveData的用户和setValue()时，数据绑定有效.
2- When you change User of LiveData and setValue() data-binding works.
3-使用EditText 2向绑定更改用户属性android:text="@={viewModel.userMutableLiveData.name}"更改LiveData的用户名，但直到用户旋转设备后，才旋转UI，直到设备旋转为止.
3- Changing User properties using EditText 2-way binding android:text="@={viewModel.userMutableLiveData.name}" changes LiveData's User's name but does not update UI until device is rotated since User is still same.
这篇关于如何与livedata进行数据绑定?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
