SavedStateHandle的使用（临时保存数据）

当使用Savedstate保存数据之后，后台进程关闭，数据也会得到保留

上图是由B站UP主longway777制作

首先在build.gradle文件中添加一下依赖

android {
        dataBinding.enabled = true
        ...
    }
    dependencies {
    implementation 'androidx.lifecycle:lifecycle-viewmodel-savedstate:2.2.0'
    .......
}

ViewModel-Savedstate 版本 2.2.0已经发布，所以B站UP主longway777中的依赖，我改为了上述版本

 

然后创建一个类继承ViewModel，在里面有有个SavedStateHandle类型的handle用来保存数据
MyViewModel.java

package com.example.viewmodelrestore;

import androidx.lifecycle.LiveData;
import androidx.lifecycle.SavedStateHandle;
import androidx.lifecycle.ViewModel;

public class MyViewModel extends ViewModel {
    private SavedStateHandle handle;

    public MyViewModel(SavedStateHandle handle) {
        if (!handle.contains("KEY_NUMBER")) {
            handle.set("KEY_NUMBER", 0);
        }
        this.handle = handle;
    }

    public LiveData getNumber() {
        return handle.getLiveData("KEY_NUMBER");
    }

    public void add() {
        handle.set("KEY_NUMBER", (int)handle.get("KEY_NUMBER") + 1);
    }
}

最后在mainactivity中实例化和绑定参数。
Mainactivity.java

public class MainActivity extends AppCompatActivity {

    MyViewModel myViewModel;
    ActivityMainBinding binding;
    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);
    }
}

UI界面