MVVM原理

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MVVM（Model–View–Viewmodel）是一种软件架构模式。
View:页面UI、动画、控件、VC层，通常有UI控件、UI事件暴露出来
ViewModel:业务数据层，通常为View层持有，接受View层事件，绑定View层控件
Model:数据模型处理层，通常是网络接口请求，本地数据处理

MVVM 登录例子

下面以RXJava框架结合登录功能具体说明整个流程：

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View:

登录界面，账号、密码、消息提示、登录按钮
activity_login.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:bind="http://schemas.android.com/tools">
    <data>
        <variable
            name="navBarHandle"
            type="com.wrs.project.module.app.common.base.nav.NavBarHandle" />
        <variable
            name="handle"
            type="com.wrs.project.module.app.login.ui.activity.LoginActivity" />
    </data>
    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/linearLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <include
            android:id="@+id/bar"
            layout="@layout/module_app_common_nav"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            bind:handle="@{navBarHandle}" />

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="22dp"
            android:text="账号:"
            android:textColor="#000000"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/bar" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="32dp"
            android:text="密码:"
            android:textColor="#000000"
            app:layout_constraintEnd_toEndOf="@+id/textView"
            app:layout_constraintStart_toStartOf="@+id/textView"
            app:layout_constraintTop_toBottomOf="@+id/textView" />

        <EditText
            android:id="@+id/accountEditTxt"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginEnd="32dp"
            android:ems="10"
            android:inputType="textPersonName"
            android:text="@={handle.accountField}"
            app:layout_constraintBottom_toBottomOf="@+id/textView"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toEndOf="@+id/textView"
            app:layout_constraintTop_toTopOf="@+id/textView" />

        <EditText
            android:id="@+id/passwordEditTxt"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:ems="10"
            android:text="@={handle.passwordFiled}"
            android:inputType="textPassword"
            app:layout_constraintBottom_toBottomOf="@+id/textView2"
            app:layout_constraintEnd_toEndOf="@+id/accountEditTxt"
            app:layout_constraintStart_toEndOf="@+id/textView2"
            app:layout_constraintTop_toTopOf="@+id/textView2" />

        <TextView
            android:id="@+id/msgTxtView"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginTop="5dp"
            android:text="@{handle.msgFiled}"
            app:layout_constraintEnd_toEndOf="@+id/passwordEditTxt"
            app:layout_constraintStart_toStartOf="@+id/passwordEditTxt"
            app:layout_constraintTop_toBottomOf="@+id/passwordEditTxt" />

        <Button
            android:id="@+id/loginBtn"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:alpha="@{handle.loginBtnAlpha}"
            android:background="#ED571D"
            android:enabled="@{handle.loginBtnEnable}"
            android:onClick="@{handle::loginBtnClick}"
            android:text="登录"
            android:textColor="#FFFFFF"
            app:layout_constraintEnd_toEndOf="@+id/passwordEditTxt"
            app:layout_constraintStart_toStartOf="@+id/textView2"
            app:layout_constraintTop_toBottomOf="@+id/msgTxtView" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

LoginActivity.java

package com.wrs.project.module.app.login.ui.activity;

import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;

import androidx.databinding.DataBindingUtil;
import androidx.databinding.ObservableField;
import androidx.lifecycle.ViewModelProvider;

import com.alibaba.android.arouter.facade.annotation.Route;
import com.wrs.project.module.app.common.base.AppBaseNavActivity;
import com.wrs.project.module.app.common.businessservice.entity.User;
import com.wrs.project.module.app.common.service.entity.Resp;
import com.wrs.project.module.app.common.vm.NewInstanceFactory;
import com.wrs.project.module.app.login.R;
import com.wrs.project.module.app.login.databinding.ActivityLoginBinding;
import com.wrs.project.module.app.login.viewmodel.LoginVM;

import io.reactivex.rxjava3.annotations.NonNull;
import io.reactivex.rxjava3.core.Observer;
import io.reactivex.rxjava3.disposables.Disposable;
import io.reactivex.rxjava3.subjects.PublishSubject;

@Route(path = LoginActivity.Router)
public class LoginActivity extends AppBaseNavActivity {
    public static final String Router = "/appLogin/SettingActivity";
    ActivityLoginBinding binding;
    public ObservableField<String> accountField =
            new ObservableField<>(); // 保存账号
    public ObservableField<String> passwordFiled =
            new ObservableField<>(); // 保存密码
    public ObservableField<Boolean> loginBtnEnable =
            new ObservableField<>(); // 绑定登录按钮能否点击
    public ObservableField<Float> loginBtnAlpha =
            new ObservableField<>();// 绑定登录按钮alpha
    public ObservableField<String> msgFiled =
            new ObservableField<>();// 绑定登录按钮alpha
    private PublishSubject accountSubject = PublishSubject.create(); // 账号监听
    private PublishSubject passwordSubject = PublishSubject.create(); // 密码监听
    private LoginVM vm;

    @Override
    protected void initUI() {
        super.initUI();
        navBarHandle.setTopTitle("登录");
        binding = DataBindingUtil.setContentView(this, R.layout.activity_login);
        binding.setNavBarHandle(navBarHandle);
        binding.setHandle(this);
        binding.accountEditTxt.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

            }

            @Override
            public void afterTextChanged(Editable s) {
                if (s.toString().trim().length() > 0) {
                    accountSubject.onNext(s.toString());
                }
            }
        });
        binding.passwordEditTxt.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

            }

            @Override
            public void afterTextChanged(Editable s) {
                if (s.toString().trim().length() > 0) {
                    passwordSubject.onNext(s.toString());
                }
            }
        });

        vm = new ViewModelProvider(getViewModelStore(), NewInstanceFactory.getInstance()).get(LoginVM.class);
        // 初始化ViewModel
        vm.init(accountSubject, passwordSubject, accountField, passwordFiled);

        // 登录按钮能否点击
        vm.getLoginEnable().subscribe(new Observer<Boolean>() {
            @Override
            public void onSubscribe(@NonNull Disposable d) {

            }

            @Override
            public void onNext(@NonNull Boolean aBoolean) {
                if (aBoolean) {
                    loginBtnEnable.set(true);
                    loginBtnAlpha.set((float) 1);
                } else {
                    loginBtnEnable.set(false);
                    loginBtnAlpha.set((float) 0.8);
                }
            }

            @Override
            public void onError(@NonNull Throwable e) {

            }

            @Override
            public void onComplete() {

            }
        });

        vm.getLoginResultSubject().subscribe(new Observer() {
            @Override
            public void onSubscribe(@NonNull Disposable d) {

            }

            @Override
            public void onNext(@NonNull Object o) {
               if (o instanceof Resp) {
                   Resp resp = (Resp)o;
                   if (resp.isSuc() && resp.getData() instanceof User) {
                       msgFiled.set("登录成功");
                   } else {
                       msgFiled.set("账号或密码错误");
                   }
               } else {
                   msgFiled.set("服务器出错");
               }
            }

            @Override
            public void onError(@NonNull Throwable e) {
               msgFiled.set("网络出错");
            }

            @Override
            public void onComplete() {

            }
        });

        // 初始化登录按钮
        accountSubject.onNext("");
        passwordSubject.onNext("");


    }

    public void loginBtnClick(View view) {
        vm.login();
    }


}

ViewModel:

1.本地验证账号、密码
2.监听登录按钮
3.登录接口反馈
LoginVM.java

package com.wrs.project.module.app.login.viewmodel;

import androidx.databinding.ObservableField;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

import com.wrs.project.module.app.common.businessservice.BusinessService;
import com.wrs.project.module.app.common.businessservice.entity.User;
import com.wrs.project.module.app.common.service.Service;
import com.wrs.project.module.app.common.service.ServiceHandle;
import com.wrs.project.module.app.common.service.entity.Resp;
import com.wrs.project.module.app.login.R;

import io.reactivex.rxjava3.annotations.NonNull;
import io.reactivex.rxjava3.core.Observable;
import io.reactivex.rxjava3.core.Observer;
import io.reactivex.rxjava3.disposables.Disposable;
import io.reactivex.rxjava3.functions.Action;
import io.reactivex.rxjava3.functions.BiFunction;
import io.reactivex.rxjava3.functions.Function;
import io.reactivex.rxjava3.subjects.PublishSubject;

public class LoginVM extends ViewModel {
    private ObservableField<String> accountField;
    private ObservableField<String> passwordField;

    private PublishSubject accountSubject;
    private PublishSubject passwordSubject;

    private PublishSubject loginResultSubject = PublishSubject.create();

    private Observable<Boolean> loginEnable;
//    private Observable<Boolean> loginEnable;

    public LoginVM() {
    }

    public void init(PublishSubject accountSubject, PublishSubject passwordSubject, ObservableField<String> accountField, ObservableField<String> passwordField) {
        this.accountSubject = accountSubject;
        this.passwordSubject = passwordSubject;
        this.accountField = accountField;
        this.passwordField = passwordField;

        // 校验账号
        Observable<Boolean> validAccount = this.accountSubject.map(new Function() {
            @Override
            public Object apply(Object o) throws Throwable {
                boolean flag = true;
                if (o instanceof String) {
                    String str = (String) o;
                    if (str.length() < 5) {
                        flag = false;
                    }
                }
                return flag;
            }
        });

        // 校验密码
        Observable<Boolean> validPassword = this.passwordSubject.map(new Function() {
            @Override
            public Object apply(Object o) throws Throwable {
                boolean flag = true;
                if (o instanceof String) {
                    String str = (String) o;
                    if (str.length() < 5) {
                        flag = false;
                    }
                }
                return flag;
            }
        });

        // 账号&密码有效登录按钮才可以点击
        loginEnable = Observable.combineLatest(validAccount, validPassword, new BiFunction<Boolean, Boolean, Boolean>() {
            @Override
            public Boolean apply(Boolean aBoolean, Boolean aBoolean2) throws Throwable {
                return aBoolean && aBoolean2;
            }
        });

    }

    public void login() {
        BusinessService.login(accountField.get(), passwordField.get(), true, new ServiceHandle<Resp<User>>(){

            @Override
            public void onFail(Exception e) {
                loginResultSubject.onError(e);
            }

            @Override
            public void onSuc(Resp<User> model) {
                loginResultSubject.onNext(model);
            }
        });
    }

    public Observable<Boolean> getLoginEnable() {
        return loginEnable;
    }

    public PublishSubject getLoginResultSubject() {
        return loginResultSubject;
    }
}

Model:

请求登录接口

package com.wrs.project.module.app.common.businessservice;

import com.wrs.project.module.app.common.businessservice.constants.InterfaceSuffix;
import com.wrs.project.module.app.common.businessservice.entity.User;
import com.wrs.project.module.app.common.service.Service;
import com.wrs.project.module.app.common.service.ServiceHandle;
import com.wrs.project.module.app.common.service.entity.Resp;
import com.wrs.project.module.common.network.HttpMethod;

import java.util.HashMap;
import java.util.Map;

public class BusinessService {
    public static void login(String account, String password, boolean toastError, ServiceHandle<Resp<User>> callBack) {
        Map<String, Object> params = new HashMap<>();
        params.put("account", account);
        params.put("password", password);
        Service.request(InterfaceSuffix.LOGIN, params, HttpMethod.POST, toastError, callBack);
    }
}

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