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移动技术开发：HandlerAsyncTask

article 2024/11/16 17:41:40

1 实验名称

Handler&AsyncTask

2 实验目的

掌握使用Handler消息传递机制和AsyncTask处理后台线程周期性的改变Activity中界面控件的属性

3 实验源代码

布局文件代码：

（1）HandlerTest

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
    android:id="@+id/constraintlayout"
    >
</androidx.constraintlayout.widget.ConstraintLayout>

（2）AsyncTask

<?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:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    >

    <Button
        android:id="@+id/downLoadBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="开始下载"
        />

    <TextView
        android:id="@+id/resultTv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:visibility="invisible"
        />

    <ProgressBar
        android:id="@+id/downLoadPb"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:visibility="invisible"
        style="?android:attr/progressBarStyleHorizontal"
        android:max="100"
        />

</LinearLayout>

Java代码：

（1）HandlerTest

package com.example.handlertest2;

import android.graphics.Color;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;

import androidx.activity.EdgeToEdge;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

public class MainActivity extends AppCompatActivity {

    private ConstraintLayout constraintLayout = null;
    private Handler handler = null;
    private int [] colors = {Color.RED,Color.GREEN,Color.BLUE,Color.YELLOW,Color.MAGENTA};
    private int currentIndex = 0;//当前颜色的下标

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        constraintLayout = findViewById(R.id.constraintlayout);
        handler = new Handler(){
            @Override
            public void handleMessage(@NonNull Message msg) {
                if (msg.what == 0x11){
                    currentIndex = (currentIndex+1)%colors.length;
                    constraintLayout.setBackgroundColor(colors[currentIndex]);
                }
            }
        };start();

    }
    private void start(){
        //创建一个每隔3秒钟就发送一个what值为0x11消息的子线程并运行起来
        new Thread(){
            @Override
            public void run() {
                while (true){
                    try {
                        Thread.sleep(3000);
                        handler.sendEmptyMessage(0x11);
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                }
            }
        }.start();
    }
}

（2）AsyncTask

package com.example.asynctasktest;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

public class MainActivity extends AppCompatActivity {
    private Button downLoadBtn = null;
    private TextView resultTv = null;
    private ProgressBar downLoadPb = null;
    //定义一个异步任务类的对象
    private DownLoadAsyncTask downLoadAsyncTask = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        downLoadBtn = findViewById(R.id.downLoadBtn);
        resultTv = findViewById(R.id.resultTv);
        downLoadPb = findViewById(R.id.downLoadPb);

        downLoadBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //创建模拟下载的异步任务类的对象，调用带参数的构造方法获取到MainActivity中的三个控件的引用
                downLoadAsyncTask = new DownLoadAsyncTask(downLoadBtn,resultTv,downLoadPb);
                //启动模拟下载的异步任务
                downLoadAsyncTask.execute(500);
            }
        });

    }
}

（3）DownLoadAsyncTask

package com.example.asynctasktest;

import android.graphics.Color;
import android.os.AsyncTask;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

public class DownLoadAsyncTask extends AsyncTask<Integer,Integer,String> {

    private Button downLoadBtn = null;
    private TextView resultTv = null;
    private ProgressBar downLoadPb = null;

    public DownLoadAsyncTask(Button downLoadBtn, TextView resultTv, ProgressBar downLoadPb) {
        this.downLoadBtn = downLoadBtn;
        this.resultTv = resultTv;
        this.downLoadPb = downLoadPb;
    }

    @Override
    protected void onPreExecute() {
        downLoadBtn.setText("正在下载中。。。");
        downLoadBtn.setEnabled(false);//将按钮设置为不可用

        resultTv.setVisibility(View.VISIBLE);//将文本框可见
        resultTv.setTextSize(24);
        resultTv.setTextColor(Color.BLUE);

        downLoadPb.setVisibility(View.VISIBLE);//将进度条可见
    }

    @Override
    protected String doInBackground(Integer... integers) {
        //模拟下载,每隔一个时间下载1%
        for (int i=0;i<101;i++){
            try {
                Thread.sleep(integers[0]);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            publishProgress(i);//发布异步任务的进度
        }
        return "下载完毕";
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        downLoadPb.setProgress(values[0]);//将publishProgress(i)方法中的i值设置为进度条的当前进度值
        resultTv.setText("当前完成了任务的"+values[0]+"%");
    }

    @Override
    protected void onPostExecute(String s) {
        resultTv.setText(s);
        downLoadBtn.setText("重新下载");
        downLoadBtn.setEnabled(true);
    }
}