android的mvvm模式

简介

官方文档

m:model
v:view(Activity)
vm:viewModel
一个view要和一个viewModel绑定

我认为就是通过view层直接操作viewModel，通过ObservableInt等基本类型或者ObservableField直接绑定layout上的值

准备工作

先在app的build.gradle中打开dataBinding

android {
    .......
    dataBinding{
        enabled = true;
    }
}

布局文件在原本布局的基础上增加根布局layout，并加入data标签,在data标签中增加要给variable，指定一个type，就是viewmodel类，name是这个类在这个xml文件中的名字，下面调用viewmodel的时候都用vm调用

<?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"
    tools:context=".MainActivity">
    <data>
        <variable
            name="vm1"
            type="cn.xwmdream.news.ViewModel"/>
    </data>
    <!--原本布局-->
    <LinearLayout>
        <TextView
            android:text="@{vm1.textt}"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </LinearLayout>
</layout>

activity中加载布局的方式也变了

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
    final ViewModel viewModel = new ViewModel(this);
    binding.setVm1(viewModel);
}

先用binding绑定布局，然后创建一个viewmodel和binding绑定，这个viewmodel会传入布局文件中当成上面指定的vm1

ViewModel

public class ViewModel {
    public ObservableField<String> textt = new ObservableField<String>("helloworld");
}

这个viewmodel中有一个textt的String类型的属性，和上面布局中的一个textview绑定，当这个textt的值发生改变时，xml中那个textview的text值也会发生改变

直接写一个例子，mvvm的RecyclerView

activity_main.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:tools="http://schemas.android.com/tools"
    tools:context=".MainActivity">
    <data>
        <variable
            name="vm1"
            type="cn.xwmdream.news.ViewModel"/>
    </data>
    <android.support.design.widget.CoordinatorLayout
        android:layout_width="match_parent"
        app:setback="@{vm1.color}"
        android:layout_height="match_parent">
        <android.support.design.widget.AppBarLayout
            android:id="@+id/bar_zone"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_scrollFlags="scroll|enterAlways|snap" />
        </android.support.design.widget.AppBarLayout>
        <TextView
            android:id="@+id/tv_errormessage"
            android:visibility="@{vm1.errorVisibility}"
            android:text="@string/error"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
        <android.support.v4.widget.SwipeRefreshLayout
            android:id="@+id/swipe_refresh"
            android:setRefreshing="@{vm1.refer}"
            android:OnRefreshListener="@{vm1.refresh}"
            android:visibility="@{vm1.listVisibility}"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior">
            <android.support.v7.widget.RecyclerView
                android:id="@+id/rv_recycler"
                android:layout_width="match_parent"
                android:layout_height="match_parent" />
        </android.support.v4.widget.SwipeRefreshLayout>
    </android.support.design.widget.CoordinatorLayout>
</layout>

MainActivity.java

package cn.xwmdream.news;
import android.databinding.DataBindingUtil;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.GridLayoutManager;
import java.util.ArrayList;
import java.util.List;
import cn.xwmdream.news.databinding.ActivityMainBinding;

/**
 * @author Administrator
 */
public class MainActivity extends AppCompatActivity implements ViewModel.DataListener {

    private List<NewBean> itemsBeanList;
    private int page = 1;
    private static final String TAG = "MainAcclivity";
    private NewAdapter adapter;
    private ActivityMainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
        final ViewModel viewModel = new ViewModel(this);
        binding.setVm1(viewModel);

        page = 0;
        //通过调用binding的绑定界面的id操作控件
        setSupportActionBar(binding.toolbar);

        binding.rvRecycler.setLayoutManager(new GridLayoutManager(this, 2));
        //创建适配器
        itemsBeanList = new ArrayList<NewBean>();
        adapter = new NewAdapter(this,itemsBeanList);
        //加载适配器
        binding.rvRecycler.setAdapter(adapter);
        viewModel.getmess(page++);
    }

    @Override
    public void updatedata(List<NewBean> newdata) {
        int count = itemsBeanList.size();
        int newcount = newdata.size();
        itemsBeanList.addAll(newdata);
        adapter.notifyItemRangeChanged(count + 1, newcount);
    }
}

ViewModel.java

package cn.xwmdream.news;

import android.databinding.BindingAdapter;
import android.databinding.ObservableBoolean;
import android.databinding.ObservableField;
import android.databinding.ObservableInt;
import android.graphics.Color;
import android.support.design.widget.CoordinatorLayout;
import android.support.v4.widget.SwipeRefreshLayout;
import android.view.View;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class ViewModel {
    public ObservableInt errorVisibility = new ObservableInt(View.GONE);
    public ObservableInt listVisibility = new ObservableInt(View.VISIBLE);
    public ObservableBoolean refer = new ObservableBoolean(false);
    public ObservableField<String> color = new ObservableField<String>("#000000");
    private List<NewBean> mlist;
    private DataListener listener;
    public ViewModel(DataListener listener){
        this.listener=listener;
    }
    public void getmess(int i){
        if (mlist == null) {
            mlist = new ArrayList<NewBean>();
        }
        mlist.clear();
        for (int j = i; j < i+10; j++) {
            mlist.add(new NewBean(String.format("标题%d",j),String.format("内容%d",j)));
        }
        listener.updatedata(mlist);
    }
    public SwipeRefreshLayout.OnRefreshListener refresh(){
        return new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                refer.set(true);
                Random random = new Random();
                getmess(random.nextInt(100));
                refer.set(false);
            }
        };

    }
    //让view层实现的接口，用户向view层发送数据
    public interface DataListener{
        void updatedata(List<NewBean> list);
    }
    @BindingAdapter("app:setback")
    public static void setbackk(CoordinatorLayout layout,ObservableField<String> color){
        layout.setBackgroundColor(Color.parseColor(color.get()));
    }
}

NewBean.java

package cn.xwmdream.news;

public class NewBean {
    private String title;
    private String content;
    public NewBean(String title, String content) {
        this.title = title;
        this.content = content;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public String getContent() {
        return content;
    }
    public void setContent(String content) {
        this.content = content;
    }
}

news_title_item.xml

<?xml version="1.0" encoding="utf-8"?>
<layout>
    <data>
        <variable
            name="vm"
            type="cn.xwmdream.news.ItemViewModel" />
    </data>
    <android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="5dp"
        android:id="@+id/cardview"
        android:onClick="@{vm.onmyclick}"
        app:cardCornerRadius="5dp">
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="@dimen/item_jian_ju"
            android:orientation="vertical">
            <!--因为有getTitle方法，所以可以直接写title-->
            <TextView
                android:id="@+id/tv_itemtitle"
                android:layout_width="match_parent"
                android:text="@{vm.title}"
                android:layout_height="wrap_content" />
            <TextView
                android:id="@+id/tv_itemcontent"
                android:text="@{vm.content}"
                android:layout_width="match_parent"
                android:layout_height="wrap_content" />
        </LinearLayout>
    </android.support.v7.widget.CardView>
</layout>

NewAdapter.java

package cn.xwmdream.news;
import android.content.Context;
import android.databinding.DataBindingUtil;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.ViewGroup;
import java.util.List;
import cn.xwmdream.news.databinding.NewsTitleItemBinding;
public class NewAdapter extends RecyclerView.Adapter<NewAdapter.ViewHolder>{
    private Context context;
    private List<NewBean> mItemList;

    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        NewsTitleItemBinding binding = DataBindingUtil.inflate(LayoutInflater.from(context),R.layout.news_title_item,viewGroup,false);
        final ViewHolder holder = new ViewHolder(binding);
        return holder;
    }
    @Override
    public void onBindViewHolder(@NonNull ViewHolder viewHolder, int i) {
        NewBean itemsBean = mItemList.get(i);
        viewHolder.bindData(itemsBean);
    }
    @Override
    public int getItemCount() {
        return mItemList.size();
    }
    static class ViewHolder extends RecyclerView.ViewHolder{
        NewsTitleItemBinding binding;
        public ViewHolder(NewsTitleItemBinding binding) {
            super(binding.cardview);
            this.binding=binding;
        }
        public void bindData(NewBean newBean){
            if (binding.getVm() == null) {
                binding.setVm(new ItemViewModel(newBean));
            }else{
                binding.getVm().setBean(newBean);
            }
        }
    }
    public NewAdapter(Context context, List<NewBean> newBeanList){
        this.context=context;
        mItemList = newBeanList;
    }
}

ItemViewModel.java

package cn.xwmdream.news;
import android.view.View;
import android.widget.Toast;
public class ItemViewModel {
    private NewBean nb;
    public ItemViewModel(NewBean newBean){
        nb=newBean;
    }
    public void onmyclick(View view){
        Toast.makeText(view.getContext(), nb.getTitle(), Toast.LENGTH_SHORT).show();
    }
    public String getTitle(){
        return nb.getTitle();
    }
    public String getContent(){
        return nb.getContent();
    }

    public void setBean(NewBean newBean) {
        this.nb=newBean;
    }
}

学到的点

• 这个程序是用了mvvm模式，其中有两个view(主页面和item页面)，和两个viewmodel
• layout中可以指定属性是viewmodel的值,如activity_main.xml的27行，错误信息的textview的visibility就和viewmodel的errorVisibility值发生绑定，当viewmodel的errorvisibility值改变了，那layout中相应的属性也就发生变化
• 当binding绑定布局后可以直接使用binding.id操作布局上的控件，如MainActivity的第30行，直接操作id为toolbar的控件
• activity_main.xml第三十行是一个SwipeRefreshLayout，他有一个监听方法，OnRefreshListener，可以使用34行的操作给他绑定这个监听方法，相当于原来findviewbyid().OnRefreshListener()，直接给他设置了一个监听，是viewmodel的那个方法，同样33行也是，本来是一个setRefreshing(boolean)的一个方法，直接在xml文件中绑定了里面的值，后续直接修改那个值就相当于原来调用的setRefreshing

• activity_main.xml的第13行，直接在xml文件中指定了一个app:setback的属性,同时在viewmodel中第52行使用@BindingAdapter({“setback”})绑定了这个setback这个方法，在xml文件中传入了一个值，这样的话在创建页面的时候就会调用vm的那个方法，传入的第一个参数是这个空间，第二个参数是传入的值，这个方法必须是静态无返回值的，而且参数必须是vm中定义的

• news_title_item.xml第14行直接设置了点击事件，对应ItemViewModel.java第九行

• NewAdapter.java第16行那个NewsTitleItemBinding是因为他拉取的文件名叫news_title_item.xml