One, transfer data between activities

1. How to transfer data?

Intent intent = new Intent(MainActivity.this, SplashActivity.class);
intent.putExtra("title", title);
startActivity(intent);

2. What data can be transmitted?

intent.putExtras(String, type)中的type：

byte
char
short
int
long
float
double
boolean
String 
Bundle
Parcelabel
CharSequence
Serializable（以上都有对应的数组类型，但Serializable无数组类型）

3. Can objects be passed?

can. Serialize when defining the class:

package com.jsc4.aboutactivity;

import java.io.Serializable;

public class UserInfo implements Serializable{
    
     // 这里要序列化implements Serializable，new出的对象就是序列化对象
    private String mUserName;
    private int mAge;

    public String getmUserName() {
    
    
        return mUserName;
    }

    public void setmUserName(String mUserName) {
    
    
        this.mUserName = mUserName;
    }

    public int getmAge() {
    
    
        return mAge;
    }

    public void setmAge(int mAge) {
    
    
        this.mAge = mAge;
    }

    public UserInfo(String userName, int age){
    
    
        mUserName = userName;
        mAge = age;
    }
}

intent.putExtra("userInfo", userInfo);  // 装包塞入
UserInfo userInfo = (UserInfo) intent.getSerializableExtra("userInfo");  // 拆包拿出，要用强制类型转换(UserInfo)

4. Can Activity return data?

把
startActivity(intent);
变成：
startActivityForResult(intent, REQUEST_CODE);

与startActivityForResult()函数配套使用的接收函数如下：
 @Override
    protected void onActivityResult(int requestCode, 
                                    int resultCode, 
                                    @Nullable Intent data) {
    
    
        super.onActivityResult(requestCode, resultCode, data);
        Log.i(TAG, "onActivityResult: requestCode="+requestCode
              +"  resultCode="+ resultCode);
        if(requestCode == REQUEST_CODE && 
           resultCode == SplashActivity.RESULT_CODE){
    
    
            if(data != null){
    
    
                String title = data.getStringExtra("title");
                textView.setText(title);
            }
        }
    }

5. Execute the task once after a delay of 1s

import android.os.Handler;

Handler mhandler = new Handler();

mhandler.postDelayed(new Runnable() {
    
    
            @Override
            public void run() {
    
    
                // 执行的内容
            }
        }, 1000);//延时1s后执行

Second, the life cycle of Activity

1. Methods involved in the life cycle

onCreate()—Newborn

onStart()-cry

onResume()—conscious

onPause()—Pause (there are other applications covered on it)

onStop()-no longer visible

onDestroy()—Destroyed

onReStart()—restarted

2. The execution process of the method:

When entering the interface for the first time, the interface will execute:

onCreate
onStart
onResume

Jump to another interface, the interface will execute:

onPause
onStop

Jump back from another interface, this interface will execute:

onRestart
onStart
onResume

Click the HOME button to return to the desktop, the interface will execute:

onPause
onStop

Click the icon to enter the interface again, the interface will execute