Question

error: package ViewModel does not exist
public abstract void setLoginViewModel(@Nullable ViewModel.LoginViewModel LoginViewModel);

错误编号：在ActivityMainBinding.java中显示错误16。这行是“ import com.jimmytrivedi.learning.mvvmloginsignupdemo.ViewModel;”

在使用DataBindings时如何解决上述异常？

我尝试过的：

使缓存无效/重启
重新检查XML属性
重命名小写字母包裹名称
-调试--stacktrace使用gradle构建

什么都没有。 Google，StackOverflow和Youtube上没有其他解决方案。

package com.jimmytrivedi.learning.mvvmloginsignupdemo.ViewModel;

MainActivity ：

import android.os.Bundle;
import android.text.TextUtils;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import com.jimmytrivedi.learning.mvvmloginsignupdemo.Model.LoginUser;
import com.jimmytrivedi.learning.mvvmloginsignupdemo.R;
import com.jimmytrivedi.learning.mvvmloginsignupdemo.ViewModel.LoginViewModel;
import com.jimmytrivedi.learning.mvvmloginsignupdemo.databinding.ActivityMainBinding;


import java.util.Objects;

public class MainActivity extends AppCompatActivity implements Observer<LoginUser> {

    private LoginViewModel loginViewModel;
    private ActivityMainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        loginViewModel = ViewModelProviders.of(MainActivity.this).get(LoginViewModel.class);

        // Inflate view and obtain an instance of the binding class.
        binding = DataBindingUtil.setContentView(MainActivity.this, R.layout.activity_main);

        // Specify the current activity as the lifecycle owner.
        binding.setLifecycleOwner(this);
        binding.setLoginViewModel(loginViewModel);
        loginViewModel.getUser().observe(MainActivity.this, this);

    }

    @Override
    public void onChanged(@Nullable LoginUser loginUser) {
        if (TextUtils.isEmpty(Objects.requireNonNull(loginUser).getEmail())) {
            binding.emailId.setError("Email Id can't be blank");
            binding.emailId.requestFocus();
        } else if (!loginUser.isEmailValid()) {
            binding.emailId.setError("Please enter valid Email Id");
            binding.emailId.requestFocus();
        } else if (TextUtils.isEmpty(Objects.requireNonNull(loginUser).getPassword())) {
            binding.password.setError("Password can't be blank");
            binding.password.requestFocus();
        } else if (!loginUser.isPasswordLengthGreaterThan5()) {
            binding.password.setError("Password length must be at least 8 digit");
            binding.password.requestFocus();
        } else {
            binding.fetchEmailId.setText(loginUser.getEmail());
            binding.fetchPassword.setText(loginUser.getPassword());
        }
    }
}

activity_main.xml

<?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"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
            name="LoginViewModel"
            type="com.jimmytrivedi.learning.mvvmloginsignupdemo.ViewModel.LoginViewModel" />
    </data>


    <androidx.core.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:isScrollContainer="true">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            tools:context=".View.MainActivity">

            <TextView
                android:id="@+id/heading"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="8dp"
                android:layout_marginTop="16dp"
                android:layout_marginEnd="8dp"
                android:lineSpacingExtra="8sp"
                android:text="Login Example Using MVVM, DataBinding with LiveData"
                android:textAlignment="center"
                android:textSize="18sp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

            <EditText
                android:id="@+id/email_id"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="32dp"
                android:layout_marginTop="32dp"
                android:layout_marginEnd="32dp"
                android:ems="10"
                android:hint="E-Mail Address"
                android:inputType="textEmailAddress"
                android:text="@={LoginViewModel.email}"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/heading" />

            <EditText
                android:id="@+id/password"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="32dp"
                android:layout_marginTop="16dp"
                android:layout_marginEnd="32dp"
                android:ems="10"
                android:hint="Password"
                android:inputType="textPassword"
                android:text="@={LoginViewModel.password}"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/email_id" />

            <Button
                android:id="@+id/login"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="32dp"
                android:layout_marginTop="32dp"
                android:layout_marginEnd="32dp"
                android:onClick="@{(v) -> LoginViewModel.onClick(v)}"
                android:text="Click to Login"
                android:textSize="18sp"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/password" />

            <TextView
                android:id="@+id/result"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="8dp"
                android:layout_marginTop="60dp"
                android:layout_marginEnd="8dp"
                android:gravity="center"
                android:text="See the Results Below From LiveDataBinding"
                android:textColor="@android:color/background_dark"
                android:textSize="16sp"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/login" />

            <TextView
                android:id="@+id/fetch_email_id"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:layout_marginEnd="8dp"
                android:text="---"
                android:textColor="@android:color/holo_blue_light"
                android:textSize="20sp"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/result" />

            <TextView
                android:id="@+id/fetch_password"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:layout_marginEnd="8dp"
                android:layout_marginBottom="32dp"
                android:text="---"
                android:textColor="@android:color/holo_blue_light"
                android:textSize="20sp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/fetch_email_id" />

        </androidx.constraintlayout.widget.ConstraintLayout>

    </androidx.core.widget.NestedScrollView>

</layout>

LoginViewModel：

    package com.jimmytrivedi.learning.mvvmloginsignupdemo.ViewModel;

    import android.view.View;

    import androidx.lifecycle.MutableLiveData;
    import androidx.lifecycle.ViewModel;

    import com.jimmytrivedi.learning.mvvmloginsignupdemo.Model.LoginUser;

    public class LoginViewModel extends ViewModel {

        public MutableLiveData<String> email = new MutableLiveData<>();
        public MutableLiveData<String> password = new MutableLiveData<>();
        private MutableLiveData<LoginUser> userMutableLiveData;

        public MutableLiveData<LoginUser> getUser() {
            if (userMutableLiveData == null) {
                userMutableLiveData = new MutableLiveData<>();
            }
            return userMutableLiveData;
        }

         public void onClick(View view) {
            LoginUser loginUser = new LoginUser(email.getValue(), password.getValue());
            userMutableLiveData.setValue(loginUser);
        }
    }

注意：

我将包装名称更改为小写字母，例如这种viewmodel，它将错误提示给不是我生成的ActivityMainImpl

Answer 1

您收到此错误，因为您已在XML文件中用大写字母定义了程序包名称。

   <variable
        name="LoginViewModel"
        type="com.jimmytrivedi.learning.mvvmloginsignupdemo.ViewModel.LoginViewModel" />

应为com.jimmytrivedi.learning.mvvmloginsignupdemo.viewmodel.LoginViewModel。 viewmodel（带有小写字母），并确保您的软件包名称为viewmodel。

Answer 2

问题在这里type="com.jimmytrivedi.learning.mvvmloginsignupdemo.ViewModel.LoginViewModel"

任何父包都必须以lowercase开头，但在您的情况下package name在Uppercase中

因此将您的ViewModel重命名为此viewmodel

您的type应该看起来像这样

 type="com.jimmytrivedi.learning.mvvmloginsignupdemo.viewmodel.LoginViewModel"

为什么数据绑定没有给出适当的例外？

2 个答案: