Android SavedStateHandle的简单使用案例

SavedSateHandle为数据存活更久而生，为避免程序被轻易地杀死，我选择用Save,下面来看看通常的使用步骤吧。

1、先导包,build.gradle(Module)

.......
defaultConfig {
        ......
        dataBinding.enabled=true
    }
}

dependencies {
    ......

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

}

2、先在活动控制器里声明你的对象，如：

package com.example.ballscorerememberpractice;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;

import com.example.ballscorerememberpractice.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {
    private ActivityMainBinding binding;//绑定视图后会出现，如有疑问可见我的dataBinding博客
    private MyViewModel myViewModel;//声明你的ViewModel
    public static String score1="score1",score2="score2";//对象的名字
}

3、创建你的ViewModel

package com.example.ballscorerememberpractice;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;
import androidx.lifecycle.SavedStateHandle;
public class MyViewModel extends ViewModel {
    private SavedStateHandle handle;

    //!!!声明构造函数，传入SavedStateHandle对象，如果不行可能是import没能自动刷新导致
    //可通过引入import androidx.lifecycle.SavedStateHandle;
    public MyViewModel(SavedStateHandle handle){
        this.handle=handle;
    }

    public MutableLiveData getaTeam(){
        if(!handle.contains(MainActivity.score1)){//判断handle是否获取过该对象.contains();
            handle.set(MainActivity.score1,0);//设置对象值
        }
        return handle.getLiveData(MainActivity.score1);//获取对象值
    }

}

4、活动创建时声明

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding= DataBindingUtil.setContentView(this,R.layout.activity_main);//设置视图
        myViewModel=new ViewModelProvider(this,new SavedStateViewModelFactory(getApplication(),this)).get(MyViewModel.class);//注意：要使用SavedStateViewModelFactory()来获取存储的handle
        binding.setData(myViewModel);//绑定数据对象到视图
        binding.setLifecycleOwner(this);//必要环节
    }

5、完成视图绑定后便可执行ViewModel的SavedStateHandle效果，若对DataBinding有疑问，看查看我的dataBinding博客。