二月四日

　　今天继续进行了一些 安卓的学习就是如果你关闭后台后继续能够保存数据主要是看关于ViewModel，Lifedata ，还有今天学的Databinding的学习

例子：主要是在后台加减以后再重新开机后不会失去数据

代码：

package com.eb.myapplicationsd;

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

import android.os.Bundle;

import com.eb.myapplicationsd.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {
        MyViewModel myViewModel;
        ActivityMainBinding binding;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        binding=DataBindingUtil.setContentView(this,R.layout.activity_main);
         myViewModel = ViewModelProviders.of(this, new SavedStateViewModelFactory(getApplication(),this)).get(MyViewModel.class);
         binding.setData(myViewModel);
         binding.setLifecycleOwner(this);
    }

    @Override
    protected void onPause() {
        super.onPause();
        myViewModel.save();
    }
}

　　

package com.eb.myapplicationsd;

import android.app.Application;
import android.content.Context;
import android.content.SharedPreferences;

import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.SavedStateHandle;
import androidx.lifecycle.ViewModel;

public class MyViewModel extends AndroidViewModel {
    SavedStateHandle savedStateHandle;
    String key=getApplication().getResources().getString(R.string.data_key);
    String shpname=getApplication().getResources().getString(R.string.shp_name);
    public MyViewModel(@NonNull Application application,SavedStateHandle savedStateHandle) {
        super(application);
        this.savedStateHandle=savedStateHandle;
        if(!savedStateHandle.contains(key))
        {

        }
    }
  public  LiveData<Integer>getNumber()
    {
        return savedStateHandle.getLiveData(key);
    }
    public void load()
    {
        SharedPreferences sharedPreferences=getApplication().getSharedPreferences(shpname, Context.MODE_PRIVATE);
        int x=sharedPreferences.getInt(key,0);
        savedStateHandle.set(key,x);
    }
    public void save()
    {
        SharedPreferences sharedPreferences=getApplication().getSharedPreferences(shpname,Context.MODE_PRIVATE);
        SharedPreferences.Editor editor=sharedPreferences.edit();
        editor.putInt(key,getNumber().getValue());
        editor.apply();
    }
    public void add(int x)
    {
        savedStateHandle.set(key,getNumber().getValue()+x);
    }
}

　　xml中的

<?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.eb.myapplicationsd.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_marginTop="152dp"
            android:text="@{String.valueOf(data.getNumber())}"
            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:layout_marginStart="73dp"
            android:layout_marginEnd="74dp"
            android:text="@string/Button_plue"
            android:onClick="@{()->data.add(1)}"
            app:layout_constraintBaseline_toBaselineOf="@+id/button2"
            app:layout_constraintEnd_toEndOf="@+id/textView"
            app:layout_constraintStart_toStartOf="parent" />

        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="296dp"
            android:layout_marginEnd="56dp"
            android:onClick="@{()->data.add(-1)}"

            android:text="@string/Button_minus"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

　　结果：

重新关节后在开启