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MVVM是什么？

Model-View-ViewMode架构，可看作MVP改进版，将此前Presenter的逻辑操作交给ViewMode中的Binder去处理

• Mode：封装数据存储及相关操作逻辑，与MVC/MVP不同的是会提供一系列实体类与UI绑定，ViewModel修改这些数据后将数据变化告诉View
• View：处理界面逻辑但不参与业务逻辑，显示ViewModel提供的数据
• ViewModel：视图模型与视图状态的合称，为View提供一个可供显示的数据模型并收集、处理这些数据，内部的Binder用于双向绑定，还可包含多个Child ViewModel

MVVM实现

前提

在build.gradle中android节点添加如下代码（最低SDK版本为API7，Gradle版本为1.5.0-alpha1）

dataBinding{enabled = true
}

Model

创建数据实体类LoginInfo

• 继承BaseObservable
• getXXX()方法通过@Bindable注解表示该方法所返回的数据被修改时会更新UI
• setXXX()方法调用notifyPropertyChanged()告诉DataBinding该字段被更改

public class LoginInfo extends BaseObservable {private String mUser;private String mPassword;public LoginInfo(String user, String password) {mUser = user;mPassword = password;}@Bindablepublic String getUser() {return mUser;}public void setUser(String user) {mUser = user;notifyPropertyChanged(BR.user);}@Bindablepublic String getPassword() {return mPassword;}public void setPassword(String password) {mPassword = password;notifyPropertyChanged(BR.password);}
}

ViewModel

LoginModel封装维护LoginInfo、点击事件、文本改变事件

public class LoginModel {private static final String DEF_USER = "song";private static final String DEF_PASSWORD = "123";public LoginInfo mInfo;private OnLoginListener mListener;public LoginModel(OnLoginListener listener) {mListener = listener;mInfo = new LoginInfo("", "");}public TextWatcher getUserTextWatcher() {return new TextWatcher() {@Overridepublic void beforeTextChanged(CharSequence s, int start, int count, int after) {}@Overridepublic void onTextChanged(CharSequence s, int start, int before, int count) {}@Overridepublic void afterTextChanged(Editable s) {mInfo.setUser(s.toString());}};}public TextWatcher getPasswordTextWatcher() {return new TextWatcher() {@Overridepublic void beforeTextChanged(CharSequence s, int start, int count, int after) {}@Overridepublic void onTextChanged(CharSequence s, int start, int before, int count) {}@Overridepublic void afterTextChanged(Editable s) {mInfo.setPassword(s.toString());}};}public interface OnLoginListener {void onLoginSuccess();void onLoginFail();}public void onLoginClick(View view) {if (mInfo.getUser().equals(DEF_USER) && mInfo.getPassword().equals(DEF_PASSWORD)) {mListener.onLoginSuccess();} else {mListener.onLoginFail();}}
}

View

xml文件根节点变为layout，布局分为

• 数据部分：声明所使用到的数据实体类以及构造该对象时的引用名
• UI部分：常规控件，可直接使用数据实体类对象中的字段、方法

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"><data><variablename="model"type="com.demo.demo0.LoginModel" /></data><LinearLayoutandroid:layout_width="match_parent"android:layout_height="match_parent"android:gravity="center_horizontal"android:orientation="vertical"><EditTextandroid:layout_width="match_parent"android:layout_height="wrap_content"android:addTextChangedListener="@{model.getUserTextWatcher}"android:hint="User"android:text="@{model.mInfo.getUser}" /><EditTextandroid:layout_width="match_parent"android:layout_height="wrap_content"android:addTextChangedListener="@{model.getPasswordTextWatcher}"android:hint="Password"android:text="@{model.mInfo.getPassword}" /><Buttonandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:onClick="@{model.onLoginClick}"android:text="Login" /></LinearLayout></layout>

MainActivity开启线程3秒后修改数据会显示在UI

• 通过DataBindingUtil.setContentView设置布局，布局名字为R.layout.ab_cd，则对应类为AbCdBinding，为其设置Model

public class MainActivity extends AppCompatActivity implements LoginModel.OnLoginListener {private static final String TAG = "MainActivity";@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);LoginModel model = new LoginModel(this);binding.setModel(model);new Thread(new Runnable() {@Overridepublic void run() {SystemClock.sleep(3000);model.mInfo.setUser("New User");model.mInfo.setPassword("New Password");}}).start();}@Overridepublic void onLoginSuccess() {Log.d(TAG, "onLoginSuccess: ");}@Overridepublic void onLoginFail() {Log.d(TAG, "onLoginFail: ");}
}