MVVM -- 3 databinding 和liveData

1.创建页面

public class MainActivity extends AppCompatActivity {

    ActivityMainLiveDataBinding viewDataBinding;
    Model model;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //绑定页面
        viewDataBinding = DataBindingUtil.setContentView(this, R.layout.activity_main_live_data);
        //绑定生命周期
        viewDataBinding.setLifecycleOwner(this);
        //获取model
        model = ViewModelProvider.AndroidViewModelFactory.getInstance(this.getApplication()).create(Model.class);
        viewDataBinding.setModel(model);
    }
}

2.xml文件

<?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="model"
            type="com.melo.app.mvvm.liveData.Model" />

    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        tools:context=".MainActivity">

        <EditText
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:hint="请输入内容"
            android:text="@={model.edtString}" />


        <TextView
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:text='@{"输入的内容是："+model.edtString}' />


    </LinearLayout>
</layout>

3.model页面

public class Model extends AndroidViewModel {

    MutableLiveData<String> edtString = new MutableLiveData<>("");

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

    public MutableLiveData<String> getEdtString() {
        return edtString;
    }
}

就这样一个简单的liveData和databinding的配合使用就搞定了。

这里有点需要说下，android 给我们提供了androidViewModel和AndroidViewModelFactory，所以刚刚demo里面的model直接继承的是androidViewModel，而不是liveData。主要是提供了application，当然若是在livedata 我们不需要application 我们也可以直接继承livedata,如下

public class Model extends ViewModel {

    MutableLiveData<String> edtString = new MutableLiveData<>("");


    public MutableLiveData<String> getEdtString() {
        return edtString;
    }
}

创建一个自己的ViewModelProvider.Factory

public class MyViewModelFactory implements ViewModelProvider.Factory {
    @NonNull
    @Override
    public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {

//方法一
//        if (modelClass.isAssignableFrom(Model.class)) {
//            return (T) new Model();
//        } else {
//            throw new IllegalArgumentException("Unknown ViewModel class");
//        }
//方法二
        try {
            return modelClass.newInstance();
        } catch (Exception e) {
            throw new IllegalArgumentException("Unknown ViewModel class");
        }
    }
}

使用方

         // 之前的
//        model = ViewModelProvider.AndroidViewModelFactory.getInstance(this.getApplication()).create(Model.class);
        //现在的
        ViewModelProvider viewModelProvider = new ViewModelProvider(this, new MyViewModelFactory());
        model = viewModelProvider.get(Model.class);