Android 两个切换时Activity的生命周期

这里说了两个Activity之间，用默认模式切换的生命周期。

代码：

1. MainActivity

package com.example.lifecycletest;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    Button a;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        a = findViewById(R.id.btn);
        a.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.w("tagchh","点击了按钮开始跳转");
                Intent intent = new Intent(MainActivity.this,SecondActivity.class);
                startActivity(intent);
            }
        });
        Log.w("tagchh","MainActivity onCreate");
    }
    @Override
    protected void onStart() {
        super.onStart();
        Log.w("tagchh","MainActivity onStart");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.w("tagchh","MainActivity onStop");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.w("tagchh","MainActivity onDestory");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.w("tagchh","MainActivity onPause");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.w("tagchh","MainActivity onResume");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.w("tagchh","MainActivity onRestart");
    }

}

2. SecondAcitvity

package com.example.lifecycletest;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

/**
 * @author by Zero_Hwa,
 * @blog https://blog.youkuaiyun.com/Zero_HWA
 * @date on 2019/10/4.
 * Do your best in the process and have a clear conscience in the end
 * PS: Not easy to write code, please indicate.
 */
public class SecondActivity extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second_activity);
        Log.w("tagchh","SecondActivity onCreate");
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.w("tagchh","SecondActivity onStart");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.w("tagchh","SecondActivity onStop");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.w("tagchh","SecondActivity onDestory");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.w("tagchh","SecondActivity onPause");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.w("tagchh","SecondActivity onResume");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.w("tagchh","SecondActivity onRestart");
    }

    @Override
    public void onBackPressed() {
        super.onBackPressed();
        Log.w("tagchh","SecondActivity点击了返回键");
    }
}

3. MainAcitvity的layout

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="goto_another_activity"
        android:id="@+id/btn"/>

</LinearLayout>

弹出界面的流程是MainActivity-点击Button-跳转到SecondActivity-点击返回-跳回MainActivity。

得到结果：

结果分析：

1.首先是MainActivity的onCreate,onStart,onResume，然后MainActivity显示出来。
2.接着点击按钮开始跳转，MainActivity的onPause之后，SecondActivity开始onCreate,onStart,onResume.
3. 第二个Activity显示出来之后，第一个Activity才onStop。
4. SecondActivity点击返回键【即back】，然后开始SecondActivity的onPause，等MainActivity的onRestart,onStart,onResume生命周期执行完之后，及MainActivity执行完之后，SecondActivity的onStop和onDestory才开始执行。

小结

默认启动模式下，Activity之间的跳转是当前的Activity先到onPause生命周期，然后等跳转目的Activity加载完，显示出来【即onResume】之后，才开始执行onStop之后的程序。

ps:其他模式还没试验不过小结这点是没错的。