android 的handler机制,安卓 handler机制的loop()为什么不会ANR?

本帖最后由 javantiger93000 于 2016-11-28 14:06 编辑

//这是我做的主活动代码，由于Android中不允许在子线程中进行UI操作，所以是基于Android的异步消息处理机制，实现了UI在子线程中的更新操作

//MainActivity.java文件

package com.example.androidthreadtest;

import android.app.Activity;

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.view.Menu;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener{

public static final int UPDATE_TEXT = 1;

private TextView text;

private Button changeText;

private Handler handler = new Handler(){

public void handleMessage(Message msg){

switch(msg.what){

case UPDATE_TEXT:

text.setText("Nice to meet you");

break;

default:

break;

}

}

};

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

text=(TextView)findViewById(R.id.text);

changeText=(Button)findViewById(R.id.change_text);

changeText.setOnClickListener(this);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.

getMenuInflater().inflate(R.menu.main, menu);

return true;

}

@Override

public void onClick(View v){

switch(v.getId()){

case R.id.change_text:

new Thread(new Runnable(){

@Override

public void run(){

Message message = new Message();

message.what = UPDATE_TEXT;

handler.sendMessage(message);

}

}).start();

break;

default:

break;

}

}

}

//activity_main.xml文件

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context=".MainActivity" >

android:id="@+id/change_text"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:text="Change Text"

/>

android:id="@+id/text"

android:layout_centerInParent="true"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/hello_world"

android:textSize="20sp" />