lateinit 属性性别尚未初始化

Question

使用数据绑定、ViewModel、LiveData (MVVM)。在我的布局中有一个用于添加员工详细信息的表单。

布局：

<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools">
<data>
    <variable
        name="viewModelAddEmployee"
        type="com.app.roomemployeedemo.viewmodel.AddEmployeeViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
    android:id="@+id/edt_lastname"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".activity.AddEmployeeActivity">
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fillViewport="true">
        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <EditText
                android:text="@{viewModelAddEmployee.firstname}"
                android:id="@+id/edt_firstname"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="40dp"
                android:ems="10"
                android:hint="Jaimin"
                android:inputType="textPersonName"
                android:maxLength="30"
                android:maxLines="1"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />
            <EditText
                android:text="@{viewModelAddEmployee.lastname}"
                android:id="@+id/tv_lastname"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:ems="10"
                android:hint="Modi"
                android:inputType="textPersonName"
                android:maxLength="30"
                android:maxLines="1"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/edt_firstname" />
            <EditText
                android:text="@{viewModelAddEmployee.age}"
                android:id="@+id/edt_age"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:ems="10"
                android:hint="25"
                android:inputType="textPersonName"
                android:maxLength="3"
                android:maxLines="1"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/tv_lastname" />
            <EditText
                android:text="@{viewModelAddEmployee.gender}"
                android:id="@+id/edt_gender"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:ems="10"
                android:hint="Gender (M/F, m/f)"
                android:inputType="textPersonName"
                android:maxLength="1"
                android:maxLines="1"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/edt_age" />
            <EditText
                android:text="@{viewModelAddEmployee.salary}"
                android:id="@+id/edt_salary"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:ems="10"
                android:hint="Salary (50000)"
                android:inputType="textPersonName"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/edt_gender" />
            <Button
                android:onClick="@{(v) -> viewModelAddEmployee.onAddEmployeeClick(v)}"
                android:id="@+id/button"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="40dp"
                android:layout_marginTop="40dp"
                android:layout_marginEnd="40dp"
                android:text="ADD NOW"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/edt_salary" />
        </androidx.constraintlayout.widget.ConstraintLayout>
    </ScrollView>
</androidx.constraintlayout.widget.ConstraintLayout>

下面是相同的 ViewModel class:

 class AddEmployeeViewModel(mContext: Context) : ViewModel(){
    var mContext=mContext
    lateinit var firstname:MutableLiveData<String>
    lateinit var lastname:MutableLiveData<String>
    lateinit var age:MutableLiveData<Int>
    lateinit var gender:MutableLiveData<Char>
    lateinit var salary:MutableLiveData<Int>
    lateinit var repositoryEmployee:EmployeeRepository
    init{
        repositoryEmployee= EmployeeRepository(mContext)
    }
    fun onAddEmployeeClick(view: View)
    {
        repositoryEmployee.onAddEmployeeClick(mContext,firstname,lastname,age,gender,salary)
    }
}

已在 Activity class 中初始化视图模型和绑定实用程序，如下所示：

class AddEmployeeActivity : AppCompatActivity() {
lateinit var viewModelAddEmployee: AddEmployeeViewModel
lateinit var binding: ActivityAddEmployeeBinding
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    viewModelAddEmployee = ViewModelProvider(this,AddEmployeeFactory(this@AddEmployeeActivity)).get(AddEmployeeViewModel::class.java)
    binding = DataBindingUtil.setContentView(
        this@AddEmployeeActivity,
        R.layout.activity_add_employee
    )
    binding?.setLifecycleOwner(this)
    binding?.viewModelAddEmployee = viewModelAddEmployee
}

}

但是，出现以下错误：

Caused by: kotlin.UninitializedPropertyAccessException: lateinit property gender has not been initialized
            at com.app.roomemployeedemo.viewmodel.AddEmployeeViewModel.getGender(AddEmployeeViewModel.kt:16)

可能是什么问题？尤其是 Char 类型的性别！！

Answer 1

您将实时数据对象声明为 lateinit var，这意味着您必须稍后在引用它们之前对其进行初始化。您需要删除 lateinit 并在创建 ViewModel 时进行初始化，或者初始化 init 块中的每个实时数据字段，如下所示：

firstname = MutableLiveData<>()

Answer 2

你能做的就是这个

fun returnName(): LiveData<String> {
        if (firstname == null) {
            firstname = MutableLiveData()
            //call some function to set value to the variable
        }
        return firstname
    }

这将确保您不会创建该列表的多个实例，并且它会 return 每次都创建相同的实例。你可以在任何你想要的变量上实现它

Answer 3

在 kotlin 中，您必须初始化 lateinit 属性。将以下行添加到 oncreate -

 gender = MutableLiveData<Char>()

Answer 4

通常，声明为具有非空类型的属性必须在构造函数中初始化。然而，这通常并不方便。例如，可以通过依赖注入或单元测试的设置方法来初始化属性。在这种情况下，您不能在构造函数中提供非空初始化程序，但在引用 class.

主体内的属性时，您仍然希望避免空检查

要处理这种情况，您可以使用 lateinit 修饰符标记属性：

样本

public class MyTest {
    lateinit var subject: TestSubject

    @SetUp fun setup() {
        subject = TestSubject()
    }

    @Test fun test() {
        subject.method()  // dereference directly
    }
}

在您的情况下，值必须加载到 ViewModel 中的变量中。

在你的情况下；

class AddEmployeeViewModel(mContext: Context) : ViewModel(){
    var mContext=mContext
    lateinit var firstname:MutableLiveData<String>
    lateinit var lastname:MutableLiveData<String>
    lateinit var age:MutableLiveData<Int>
    lateinit var gender:MutableLiveData<Char>
    lateinit var salary:MutableLiveData<Int>
    lateinit var repositoryEmployee:EmployeeRepository
        init{
              repositoryEmployee= EmployeeRepository(mContext)
              lastname = MutableLiveData<String>()
              firstname = MutableLiveData<String>()
              age = MutableLiveData<Int>()
              gender = MutableLiveData<Char>()
              salary = MutableLiveData<Int>()
        }
fun onAddEmployeeClick(view: View)
    {
        repositoryEmployee.onAddEmployeeClick(mContext,firstname,lastname,age,gender,salary)
    }
}

最佳实践

private val _sampleVar = MutableLiveData<String>()
val sampleVar: LiveData<String>
   get() = _sampleVar

lateinit 属性性别尚未初始化

lateinit property gender has not been initialized

android

mvvm

android-databinding

android-livedata

android-viewmodel

lateinit 属性 性别尚未初始化

lateinit property gender has not been initialized

android

mvvm

android-databinding

android-livedata

android-viewmodel

lateinit 属性性别尚未初始化