JetPack系列之ViewModel进行数据共享

前言

目前Fragment的传值可以使用Bundle,JetPack使用数据分离的思想,利用ViewModel来达到Fragment之间传值的目的,下面我来讲解下。

开始

这篇文章涉及了Databing,Navigation,ViewModel和LiveData等知识点,初看难度较大,后期补上其他教程。

用例需求

Fragment1中使用SeekBar修改值,Fragment2中跳转后能查看,反之亦然。

代码编写

• GlobalViewModel的创建,该类提供了对数据的增加和查询的操作

public class GlobalViewModel extends ViewModel {
	private MutableLiveData<Integer> mutableLiveData;


    public void add(Integer x){
        mutableLiveData.setValue(mutableLiveData.getValue() + x);
        if (mutableLiveData.getValue() < 0) {
            mutableLiveData.setValue(0);
        }
    }

    public MutableLiveData<Integer> getNumber(){
        if (mutableLiveData == null) {
            mutableLiveData = new MutableLiveData<>();
            mutableLiveData.setValue(0);
        }
        return mutableLiveData;
    }
}

• 编写HomeFragment

注意，获取ViewModel对象时需要传入Activity,数据才能共享。

HomeFragment

public class HomeFragment extends Fragment {


    public HomeFragment() {
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        GlobalViewModel viewModel = ViewModelProviders.of(getActivity()).get(GlobalViewModel.class);
        FragmentHomeBinding binding = DataBindingUtil.inflate(inflater, R.layout.fragment_home, container,
                false);
        binding.setData(viewModel);
        binding.setLifecycleOwner(this);
        binding.seekBar.setProgress(viewModel.getNumber().getValue());
        binding.seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                binding.getData().getNumber().setValue(progress);
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {

            }
        });
        binding.btnGotoDetail.setOnClickListener(v -> {
            NavController navController = Navigation.findNavController(v);
            navController.navigate(R.id.action_homeFragment_to_detailFragment);
        });
        return binding.getRoot();
    }
}

fragment_home

<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="data"
            type="com.martin.jetmo.jetpack.viewmodel.GlobalViewModel" />
    data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".fragment.HomeFragment">

        <TextView
            android:id="@+id/tvProcessNumber"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{String.valueOf(data.number)}"
            android:textSize="24sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.221" />

        <SeekBar
            android:id="@+id/seekBar"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/tvProcessNumber"
            app:layout_constraintVertical_bias="0.158" />

        <Button
            android:id="@+id/btnGotoDetail"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="GoTo"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/tvProcessNumber"
            app:layout_constraintVertical_bias="0.332" />
    androidx.constraintlayout.widget.ConstraintLayout>
layout>

DetailFragment

public class DetailFragment extends Fragment {


    public DetailFragment() {

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        FragmentDetailBinding binding = DataBindingUtil.inflate(inflater, R.layout.fragment_detail,
                container, false);
        GlobalViewModel viewModel = ViewModelProviders.of(getActivity()).get(GlobalViewModel.class);
        binding.textView2.setText(String.valueOf(viewModel.getNumber().getValue()));
        binding.setData(viewModel);
        binding.setLifecycleOwner(this);
        binding.back.setOnClickListener(v -> {
            NavController navController = Navigation.findNavController(v);
            navController.navigate(R.id.action_detailFragment_to_homeFragment);
        });
        return binding.getRoot();

    }
}

fragment_detail

<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="data"
            type="com.martin.jetmo.jetpack.viewmodel.GlobalViewModel" />
    data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".fragment.DetailFragment">


        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{String.valueOf(data.number)}"
            android:textSize="24sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.182" />

        <Button
            android:id="@+id/button3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="@{()->data.add(1)}"
            android:text="+"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toStartOf="@+id/button4"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.538" />

        <Button
            android:id="@+id/button4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="@{()->data.add(-1)}"
            android:text="-"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/button3"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.538" />

        <Button
            android:id="@+id/back"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="204dp"
            android:text="back"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.486"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="1.0" />


    androidx.constraintlayout.widget.ConstraintLayout>
layout>

参考文章

• ViewModel 概览