uiHandler 简单演示

package com.zhy.thread_baidu;import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;public class MainActivity extends AppCompatActivity implements View.OnClickListener {//创建消息码private static final int MESSAGE_GetGame_OK = 1;private static final int MESSAGE_GetGame_ERROR = 2;private Button m_btn;private ImageView m_imageView;private String m_imageUrl = "";//创建一个uiHandlerprivate Handler uiHandler = new Handler() {@Overridepublic void handleMessage(@NonNull Message msg) {super.handleMessage(msg);switch (msg.what) {case MESSAGE_GetGame_OK: {System.out.println("UI thread get Message from sub thread,ok");Bitmap bm = (Bitmap) msg.obj;displayImage(bm);break;}case MESSAGE_GetGame_ERROR: {System.out.println("UI thread get message from sub thread,error");break;}default:break;}//switch (msg.what)}//public void handleMessage}; //private Handler uiHandler = new Handler()@Overridepublic void onClick(View v) {if (v.getId() == R.id.handlerBtn) {m_imageUrl = getImageUrlFromUI();// 创建子线程Thread thread = new Thread(new Runnable() {@Overridepublic void run() {try {//下载图片Bitmap bmBitmap = downloadImage(m_imageUrl);//创建消息Message msg = Message.obtain();msg.what = MESSAGE_GetGame_OK;msg.obj = bmBitmap;//发送消息uiHandler.sendMessage(msg);} catch (IOException e) {e.printStackTrace();//创建消息Message msg = Message.obtain();msg.what = MESSAGE_GetGame_ERROR;uiHandler.sendMessage(msg);}}});thread.start();}}@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);m_btn = (Button) findViewById(R.id.handlerBtn);m_imageView = (ImageView) findViewById(R.id.handlerImageView);m_btn.setOnClickListener(this);}private Bitmap downloadImage(String urlString) throws IOException {if (urlString.equals("")) {System.out.println("Url is empty.");return null;}URL url = new URL(urlString);URLConnection conn = url.openConnection();return BitmapFactory.decodeStream(conn.getInputStream());}public void displayImage(Bitmap bm) {m_imageView.setImageBitmap(bm);}private String getImageUrlFromUI() {//预配URLreturn "https://ss0.bdstatic.com/94oJfD_bAAcT8t7mm9GUKT-xh_/timg?image&quality=100&size=b4000_4000&sec=1591682139&di=de4ebaf40b6319d647501aceda38b4cd&src=http://n.sinaimg.cn/sinacn/w690h460/20180226/8a57-fyrwsqi4293849.jpg";}
}

修改AndroidManifest.xml

//添加权限
<uses-permission android:name="android.permission.INTERNT"/>

activity.xml

<?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"android:orientation="vertical"tools:context=".MainActivity"><TextViewandroid:id="@+id/textView2"android:layout_width="match_parent"android:layout_height="wrap_content"android:text="点击确定，获得图片"android:textSize="26dp"android:layout_marginTop="30dp"android:gravity="center"/><ImageViewandroid:id="@+id/handlerImageView"android:layout_width="match_parent"android:layout_height="311dp"android:layout_marginTop="50dp"app:srcCompat="@drawable/ic_launcher_background" /><Buttonandroid:id="@+id/handlerBtn"android:layout_width="195dp"android:layout_height="wrap_content"android:layout_marginLeft="100dp"android:layout_marginTop="50dp"android:layout_marginRight="30dp"android:text="Button" />
</LinearLayout>