通过ViewModel实现的数据共享符合Android的MVC设计模式，将数据独立出来

实现的Demo

1、主页面通过SeekBar 来改变数字的值

2、点击进入就进入第二个界面，但是数据还是共享的

3、随便加两个数字上去，再次切换

4、发现数据还是共享的

下面是具体实现步骤：

1、建立两个Fragment（使用了Binding 和 Navigation）

一点要添加Binding 和 Navigation 不然做不了

2、建立一个继承于ViewModel的类

3、分别在两个Fragment的代码中使用继承于ViewModel的那个类，就可以实现数据共享

下面是具体代码：

1、继承于ViewModel的类

package com.example.naviation01;import androidx.lifecycle.MutableLiveData;import androidx.lifecycle.ViewModel;public class MyViewMode extends ViewModel {  private MutableLiveData number;  public MutableLiveData getNumber(){    if(this.number == null){      this.number = new MutableLiveData<>();      this.number.setValue(0);    }    return this.number;  }  public void add(int x){    this.number.setValue(this.number.getValue()+x);    if(this.number.getValue() < 0){      this.number.setValue(0);    }  }}

2、Fragment 主页

package com.example.naviation01;import android.os.Bundle;import androidx.databinding.DataBindingUtil;import androidx.fragment.app.Fragment;import androidx.fragment.app.FragmentController;import androidx.lifecycle.ViewModel;import androidx.lifecycle.ViewModelProvider;import androidx.lifecycle.ViewModelProviders;import androidx.navigation.NavController;import androidx.navigation.Navigation;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.SeekBar;import com.example.naviation01.databinding.FragmentHomeBinding;/** * A simple {@link Fragment} subclass. */public class HomeFragment extends Fragment {  public HomeFragment() {    // Required empty public constructor  }  @Override  public View onCreateView(LayoutInflater inflater, ViewGroup container,               Bundle savedInstanceState) {    // Inflate the layout for this fragment    final MyViewMode myViewMode;    myViewMode = ViewModelProviders.of(getActivity()).get(MyViewMode.class);    FragmentHomeBinding binding;    binding = DataBindingUtil.inflate(inflater,R.layout.fragment_home,container,false);    binding.setData(myViewMode);    binding.setLifecycleOwner(getActivity());    binding.seekBar.setProgress(myViewMode.getNumber().getValue());    binding.seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {      @Override      public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {        myViewMode.getNumber().setValue(progress);      }      @Override      public void onStartTrackingTouch(SeekBar seekBar) {      }      @Override      public void onStopTrackingTouch(SeekBar seekBar) {      }    });    binding.button.setOnClickListener(new View.OnClickListener() {      @Override      public void onClick(View v) {        NavController controller = Navigation.findNavController(v);        controller.navigate(R.id.action_homeFragment_to_detailFragment);      }    });    return binding.getRoot();    //return inflater.inflate(R.layout.fragment_home, container, false);  }}

xml

                                     

3、Fragment 副页

package com.example.naviation01;import android.os.Bundle;import androidx.databinding.DataBindingUtil;import androidx.fragment.app.Fragment;import androidx.lifecycle.ViewModelProviders;import androidx.navigation.NavController;import androidx.navigation.Navigation;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import com.example.naviation01.databinding.FragmentDetailBinding;/** * A simple {@link Fragment} subclass. */public class DetailFragment extends Fragment {  public DetailFragment() {    // Required empty public constructor  }  @Override  public View onCreateView(LayoutInflater inflater, ViewGroup container,               Bundle savedInstanceState) {    // Inflate the layout for this fragment    MyViewMode myViewMode;    myViewMode = ViewModelProviders.of(getActivity()).get(MyViewMode.class);    FragmentDetailBinding binding;    binding = DataBindingUtil.inflate(inflater,R.layout.fragment_detail,container,false);    binding.setDate(myViewMode);    binding.setLifecycleOwner(getActivity());    binding.button4.setOnClickListener(new View.OnClickListener() {      @Override      public void onClick(View v) {        NavController controller = Navigation.findNavController(v);        controller.navigate(R.id.action_detailFragment_to_homeFragment);      }    });    return binding.getRoot();    //return inflater.inflate(R.layout.fragment_detail, container, false);  }}

xml

                         

                 

4、xml Main_Activity