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handler+message [message mechanism]

2022-07-30 04:34:00 【bad ambassador】

作者：不良使
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Python+Android
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引言

handler Mainly to solve the time-consuming operation of the same page.Take a look before looking at the methodAndroidThe time-consuming operation of the medium message mechanism is generally not performed in the main thread,Because it may cause blockage,加载慢,程序崩溃等.在Android项目中经常有碰到这样的问题,在子线程中完成耗时操作之后要更新UI,下面就自己经历的一些项目总结一下更新的方法.There are many ways to solve time-consuming operations that the main thread cannot complete.

🥭🥭1、Handler（消息机制）
🥭🥭2、runOnUiThread（在子线程中new一个主线程）
🥭🥭3、Looper

这篇文章讲解Handler（消息机制）

handler实现

handlerThe only way to deal with time-consuming operations that cannot be performed by child threads is 等价于 Assign time-consuming operations to others by way of tasks,The operation of assigning tasks is performed in the child thread（非耗时操作）.举个例子吧,It takes a long time for a big company to do a big project,But assigning to a subsidiary does not require this time-consuming operation.It is only necessary to perform assignment of tasks to subsidiaries,The subsidiary can accept the project after completion.It is equivalent to completing a large project independently to the end, only needing to assign tasks and review project operations.

Create handlers and messages,发送数据.

Handler handler=new Handler();
Message message=new Message();
message.what=111;
message.obj=数据;//Data can be of primitive types、对象、列表、数组等
handler.sendMessage(message);

下面对handlerSome nouns and related terms are analyzed.

Handler handler=new Handler();
Handler：处理者,负责Message的发送及处理.使用Handler时,需要实现handleMessage(Message msg)方法来对特定的Message进行处理,例如更新UI等.new Handler()Equivalent to creating a handler.

Message message=new Message();
Message：消息,其中包含了消息ID,消息处理对象以及处理的数据等,由MessageQueue统一列队,终由Handler处理.new Message()相当于创建一个Message对象,Store data for later data transmission（任务分配）做准备

Speaking of newsmessage,How can you forget about message queues？
MessageQueue：消息队列,用来存放Handler发送过来的消息,并按照FIFO规则执行.当然,存放Message并非实际意义的保存,而是将Message以链表的方式串联起来的,等待Looper的抽取.looper下面会说

message.what=111;
这个相当于View.OnClickListener重写方法onClick(View v)的v.getId(),都是整型.

The following will use this,But it is recommended to write it in a class,便于项目管理.

message.obj=数据;//Data can be of primitive types、对象、列表、数组等
This code is the real core,Equivalent to assigning a value to thismessage(消息对象),The data type at this time may be that the data may be a primitive type、对象、列表、数组等

handler.sendMessage(message);
发送消息,将消息发送出去.

重写handleMessage方法,接收数据,执行耗时操作.

@Override
    public boolean handleMessage(@NonNull Message msg) {
    
        switch (msg.what){
    
            case 111:
                Toast.makeText(LoginMainActivity.this, "登陆失败" + mEtPassWord.getText().toString().trim(), Toast.LENGTH_SHORT).show();
                break;
            default:
                break;
        }
        return false;
    }

上面的handlerSending messages can be based on message.what=111; Send different data,handleMessage可以通过switch~case 区分出来.

handler有两种方法实现,原理都一样,一个直接new,A calling interface.There are two ways to choose according to the project.The above is the first method,但是原理是一样的,下面总结一下

第一种,接口implements

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发送数据

Handler handler=new Handler();
Message message=new Message();
message.what=111;
message.obj=数据;//Data can be of primitive types、对象、列表、数组等
handler.sendMessage(message);

接收数据,执行耗时操作

@Override
    public boolean handleMessage(@NonNull Message msg) {
    
        switch (msg.what){
    
            case 111:
                Toast.makeText(LoginMainActivity.this, "登陆失败" + mEtPassWord.getText().toString().trim(), Toast.LENGTH_SHORT).show();
                break;
            default:
                break;
        }
        return false;
    }

第二种,new个

The child thread sends data

private void updateWeather() {
      
        new Thread(new Runnable(){
      
            @Override  
            public void run() {
      
                //耗时操作,完成之后发送消息给Handler,完成UI更新; 
                mHandler.sendEmptyMessage(0);  
                //传递数据
                Message msg =new Message();  
                msg.obj = "数据";//Data can be of primitive types、对象、列表、数组等 
                mHandler.sendMessage(msg);  
            }  
        }).start();  
    }

主线程接收数据

Handler mHandler = new Handler() {
      
  
        @Override  
        public void handleMessage(Message msg) {
      
            super.handleMessage(msg);  
            switch (msg.what) {
      
            case 0:  
                //拿到数据,执行耗时操作 
                String data = (String)msg.obj;  
                updateWeather();  
                textView.setText(data);  
                break;  
            case 1:
            ......
            break;

            ...


            default:  
                break;  
            }  
        }  
  
    };