SavedStated

 

通过之前的努力，引用viewmodel而解决了屏幕翻转，语言切换而导致的数据丢失

现在引入新的模式ViewModelSavedState来使得Activity重新创建时UI数据也不会丢失

 

 首先是Activity中的导入viewmodel改变

myViewModel=new ViewModelProvider(this,new SavedStateViewModelFactory(getApplication(),this)).get(MyViewModel.class);

需要导入两个依赖

implementation 'androidx.lifecycle:lifecycle-viewmodel-savedstate:2.2.0'
implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

其次MyViewModel中改变也很多，直接上代码吧

package com.example.viewmodelrestore;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.SavedStateHandle;
import androidx.lifecycle.ViewModel;

public class MyViewModel extends ViewModel {
    private  SavedStateHandle handle;
    public  MyViewModel(SavedStateHandle handle){
        this.handle= handle;//这里是当activity重新创建时，要把之前的数重新导入
    }

    public MutableLiveData<Integer> getNumber() {
        if(!handle.contains(MainActivity.KEY_NUMBER)){
            handle.set(MainActivity.KEY_NUMBER,0);
        }
        return handle.getLiveData(MainActivity.KEY_NUMBER);
    }
    public void add(){
        getNumber().setValue(getNumber().getValue()+1);
    }
}

MainActivity

package com.example.viewmodelrestore;


import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;
import android.os.Bundle;
import com.example.viewmodelrestore.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {
    ActivityMainBinding binding;
    MyViewModel myViewModel;
    public final static String KEY_NUMBER="my_number";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding= DataBindingUtil.setContentView(this,R.layout.activity_main);
        myViewModel=new ViewModelProvider(this,new SavedStateViewModelFactory(getApplication(),this)).get(MyViewModel.class);
        binding.setData(myViewModel);
        binding.setLifecycleOwner(this);

    }

}

activity_main

<?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="data"
            type="com.example.viewmodelrestore.MyViewModel" />
    </data>

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

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="175dp"
            android:layout_marginTop="162dp"
            android:layout_marginEnd="177dp"
            android:layout_marginBottom="118dp"
            android:text="@{String.valueOf(data.getNumber)}"
            app:layout_constraintBottom_toTopOf="@+id/button"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/button1"
            android:onClick="@{()->data.add()}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

 

标签：SavedStated,handle,androidx,public,import,MyViewModel,lifecycle
来源： https://www.cnblogs.com/nian-nian/p/15771706.html