Android MVVM实践(ViewModel+LiveData+DataBinding)

Andorid常用的开发模式有MVP MVVM，MVP与MVVM不同之处在于MVP中的Presenter持有View层的引用，而MVVM中的ViewModel并未持有View层的引用，而是通过观察者模式完成数据的交互，从而ViewModel层与View层也完成解耦。

这里使用Jetpack组件ViewModel+LiveData+DataBinding完成一个MVVM的例子

目录结构如上所示：

Model层处理网络请求或从数据库获取数据 ;

View层负责UI展示及用户交互；

ViewModel层负责数据的处理及分发；

LoginActivity代码如下

/**
 * MVVM中  M为业务层 V为视图层 VM相当于MVP中的P,但是VM不持有V的引用
 */
public class LoginActivity extends AppCompatActivity {

    public static void actionStart(Context context) {
        Intent intent = new Intent(context, LoginActivity.class);
        context.startActivity(intent);
    }

    private ActivityLoginBinding binding;
    private LoginViewModel viewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        binding = DataBindingUtil.setContentView(this, R.layout.activity_login);

        //获取viewModel实例
        viewModel = new ViewModelProvider(this, new ViewModelProvider.AndroidViewModelFactory(getApplication()))
                .get(LoginViewModel.class);
        binding.setViewModel(viewModel);
        //双向绑定需要加这句，否则不起作用
        binding.setLifecycleOwner(this);

        initListener();
    }

    private void initListener() {

        //相当于网络请求回调，观察回调数据变化
        viewModel.getLoginResponseLD().observe(LoginActivity.this, loginResponse -> {
            boolean loginSuccess = loginResponse.isLoginSuccess();
            if (loginSuccess) {
                Toast.makeText(LoginActivity.this, loginResponse.getMessage(), Toast.LENGTH_SHORT).show();
                finish();
            } else {
                Toast.makeText(LoginActivity.this, loginResponse.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });


        binding.btnLogin.setOnClickListener(v -> {
            String loginName = viewModel.getLoginNameLD().getValue();
            String pwd = viewModel.getPwdLD().getValue();

            if (TextUtils.isEmpty(loginName)) {
                Toast.makeText(LoginActivity.this, "请输入用户名", Toast.LENGTH_SHORT).show();
                return;
            }
            if (TextUtils.isEmpty(pwd)) {
                Toast.makeText(LoginActivity.this, "请输入密码", Toast.LENGTH_SHORT).show();
                return;
            }

            //请求登录
            viewModel.login();
        });
    }
}

布局文件代码，需转化为data binding layout，引入ViewModel完成双向绑定

<?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="viewModel"
            type="com.example.mvvmdemo.viewmodel.LoginViewModel" />

        <import type="android.view.View" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/cl_root"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".view.LoginActivity">

        <EditText
            android:id="@+id/et_login_name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="请输入用户名"
            android:text="@={viewModel.loginNameLD}"
            android:textColor="@color/black"
            app:layout_constraintTop_toTopOf="parent" />

        <EditText
            android:id="@+id/et_pwd"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="请输入密码"
            android:inputType="textPassword"
            android:text="@={viewModel.pwdLD}"
            android:textColor="@color/black"
            app:layout_constraintTop_toBottomOf="@id/et_login_name" />

        <Button
            android:id="@+id/btn_login"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="登录"
            app:layout_constraintTop_toBottomOf="@id/et_pwd" />


        <ProgressBar
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:visibility="@{viewModel.loadingLD?View.VISIBLE:View.GONE}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

LoginViewModel代码

/**
 * @author xushibin
 * @date 12/20/21
 * description：
 */
public class LoginViewModel extends AndroidViewModel {

    public LoginViewModel(@NonNull Application application) {
        super(application);
    }

    private MutableLiveData<String> loginNameLD = new MutableLiveData<>();
    private MutableLiveData<String> pwdLD = new MutableLiveData<>();
    private MutableLiveData<Boolean> loadingLD = new MutableLiveData<>();

    private MutableLiveData<LoginResponse> loginResponseLD = new MutableLiveData<>();

    public MutableLiveData<String> getLoginNameLD() {
        return loginNameLD;
    }

    public void setLoginNameLD(MutableLiveData<String> loginNameLD) {
        this.loginNameLD = loginNameLD;
    }

    public MutableLiveData<String> getPwdLD() {
        return pwdLD;
    }

    public void setPwdLD(MutableLiveData<String> pwdLD) {
        this.pwdLD = pwdLD;
    }

    public MutableLiveData<Boolean> getLoadingLD() {
        return loadingLD;
    }

    public void setLoadingLD(MutableLiveData<Boolean> loadingLD) {
        this.loadingLD = loadingLD;
    }

    public MutableLiveData<LoginResponse> getLoginResponseLD() {
        return loginResponseLD;
    }

    public void setLoginResponseLD(MutableLiveData<LoginResponse> loginResponseLD) {
        this.loginResponseLD = loginResponseLD;
    }

    public void login() {
        loadingLD.setValue(true);
        HttpRequest.login(loginNameLD.getValue(), pwdLD.getValue(), new CallBackLis() {
            @Override
            public void success(String backStr) {
                loadingLD.setValue(false);
                LoginResponse loginResponse = new LoginResponse();
                loginResponse.setLoginSuccess(true);
                loginResponse.setMessage("登录成功！");
                loginResponseLD.setValue(loginResponse);
            }

            @Override
            public void failure(int errorCode, String error) {
                loadingLD.setValue(false);
                LoginResponse loginResponse = new LoginResponse();
                loginResponse.setLoginSuccess(false);
                loginResponse.setMessage(error);
                loginResponseLD.setValue(loginResponse);
            }
        });
    }
}

HttpRequest代码，模拟网络请求操作

/**
 * @author xushibin
 * @date 12/20/21
 * description：
 */
public class HttpRequest {

    /**
     * 模拟网络请求操作 example/123456登录成功
     *
     * @param loginName
     * @param pwd
     * @param callBackLis
     */
    public static void login(String loginName, String pwd, CallBackLis callBackLis) {

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                new Handler(Looper.getMainLooper()).post(new Runnable() {
                    @Override
                    public void run() {

                        if (TextUtils.equals(loginName, "example") && TextUtils.equals(pwd, "123456")) {
                            callBackLis.success("登录成功");
                        } else {
                            callBackLis.failure(101, "登录失败");
                        }
                    }
                });
            }
        }).start();

    }

}

最后附上完整demo，点击查看https://github.com/xsb0426/MVVMDemo