DataBinding基本功能使用笔记

DataBinding是一个实现数据和UI绑定的框架，是构建MVVM模式的一个关键工具。
基本用法
1 Gradle启用DataBinding

Android{
    ….
    databinding{
    enabeled true
 }
 }

2 创建viewmodel包，包下创建一个UserViewModel,这里实现了双向绑定，需要注意set方法加notifyPropertyChanged()，get方法加@Bindable注解;

import android.databinding.BaseObservable;
import android.databinding.Bindable;

import com.android.databinding.library.baseAdapters.BR;


/**
 * Created by chentanrong on 2017/3/22.
 */

public class UserViewModel extends BaseObservable{

private boolean gender;//男--true 女--false
private String username;
private String password;


public UserViewModel(boolean gender, String username, String password) {
this.gender = gender;
this.username = username;
this.password = password;
    }

@Bindable
public boolean isGender() {
return gender;
    }

public void setGender(boolean gender) {
this.gender = gender;
        notifyPropertyChanged(BR.gender);
    }
@Bindable
public String getUsername() {
return username;
    }

public void setUsername(String username) {
this.username = username;
        notifyPropertyChanged(BR.password);
    }
@Bindable
public String getPassword() {
return password;
    }

public void setPassword(String password) {
this.password = password;
        notifyPropertyChanged(BR.password);
    }

@Override
public String toString() {
return "UserViewModel{" +
"gender=" + gender +
", username='" + username + '\'' +
", password='" + password + '\'' +
'}';
    }
}

2 在需要绑定的xml中，引用这个ViewMode，其如在activity_main.xml中绑定：

<?xml version="1.0" encoding="utf-8"?>
<layout>

<data>

<variable
 name="userViewModel"
type="com.yulintu.databind.viewmodel.UserViewModel" />
</data>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.yulintu.databind.MainActivity">

<EditText
 android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@={userViewModel.username}" />//加“=”才能双向绑定

<EditText
 android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@={userViewModel.password}" />

<RadioGroup
 android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<RadioButton
 android:id="@+id/radioButtonM"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:checked="@={userViewModel.gender}"
android:text="男" />

<RadioButton
 android:id="@+id/radioButtonF"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:checked="@={!userViewModel.gender}"
android:text="女" />
</RadioGroup>
<Button
 android:id="@+id/buttonRegister"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="注册" />

</LinearLayout>
</layout>

3 在mainActitiy中，DataBindingh会根据activity_main.xml的名字自动生成一个ActivityMainBinding的类，此时需要将setContentView( R.layout.activity_main)换成ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);

public class MainActivity extends AppCompatActivity {

private ActivityMainBinding binding;
private UserViewModel userViewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        binding= DataBindingUtil.setContentView(this,R.layout.activity_main);
        userViewModel =new UserViewModel(true,"chentanrong","123454");
//当viewModel中的值发生改变时的回调
        Observable.OnPropertyChangedCallback onPropertyChangedCallback=new Observable.OnPropertyChangedCallback() {
@Override
public void onPropertyChanged(Observable observable, int i) {
if(i==BR.gender&&observable instanceof UserViewModel ){
                    Toast.makeText(getApplicationContext(),((UserViewModel) observable).isGender()?"男":"女", Toast.LENGTH_LONG).show();
                }
if(i==BR.username&&observable instanceof UserViewModel ){
                    Toast.makeText(getApplicationContext(),((UserViewModel) observable).getUsername(), Toast.LENGTH_LONG).show();
                }
if(i==BR.password&&observable instanceof UserViewModel ){
                    Toast.makeText(getApplicationContext(),((UserViewModel) observable).getPassword(), Toast.LENGTH_LONG).show();
                }
            }
        };
        userViewModel.addOnPropertyChangedCallback(onPropertyChangedCallback);
//界面点击事件的回调
        binding.buttonRegister.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
                Toast.makeText(getApplicationContext(), userViewModel.toString(), Toast.LENGTH_LONG).show();
            }
        });
        binding.setUserViewModel(userViewModel);

    }
}