[移动开发]saveinstancestate用法（Activity销毁时保存数据）

activity展示点击按钮改变数字，activity销毁重建时数字显示改变之后的

核心是状态保存到这个方法里面

    @Override
    public void onSaveInstanceState(@NonNull final Bundle outState) {
        Log.e("wy","run: "+ "onSaveInstanceState");
        super.onSaveInstanceState(outState);
        outState.putInt("myInt",i);

    }

全代码

package com.dongnaoedu.jetpackstudy;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

public class ViewModelActivity extends AppCompatActivity {

    private TextView mTextView;
    int i;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_view_model);
        mTextView = (TextView) findViewById(R.id.textView);
        if(savedInstanceState!=null){
            i=savedInstanceState.getInt("myInt");
            mTextView.setText(i+"");
            Log.e("wy","run: "+ i);
        }

    }

    public void plus(View view) {
        i++;
        mTextView.setText(i+"");
    }

    @Override
    public void onSaveInstanceState(@NonNull final Bundle outState) {
        Log.e("wy","run: "+ "onSaveInstanceState");
        super.onSaveInstanceState(outState);
        outState.putInt("myInt",i);

    }


}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ViewModelActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="242dp"
        android:layout_height="0dp"
        android:layout_marginTop="209dp"
        android:layout_marginBottom="243dp"
        android:text="TextView"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.603"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="MissingConstraints" />

    <Button
        android:id="@+id/button"
        android:layout_width="207dp"
        android:layout_height="0dp"
        android:layout_marginBottom="76dp"
        android:onClick="plus"
        android:text="+"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/textView"
        tools:ignore="MissingConstraints" />
</androidx.constraintlayout.widget.ConstraintLayout>