android中的异步任务

墨蓝 2023-01-02 03:21 150阅读 0赞

前些天发现了一个巨牛的人工智能学习网站，通俗易懂，风趣幽默，忍不住分享一下给大家。[点击跳转到教程][Link 1]  
还是以下载并安装最新APK例子

package com.hbk.layoutdemo;
    
    
    import java.io.File;
    import java.io.FileOutputStream;
    import java.io.InputStream;
    import java.net.HttpURLConnection;
    import java.net.URL;
    
    import android.app.Activity;
    import android.app.ProgressDialog;
    import android.content.Intent;
    import android.net.Uri;
    import android.os.AsyncTask;
    import android.os.Bundle;
    import android.os.SystemClock;
    import android.view.View;
    
    /** * * @author 黄宝康 * */
    public class MainActivity extends Activity { 
    
    
    	private File apkFile;
    	private ProgressDialog dialog;
    	
    
    	@Override
    	protected void onCreate(Bundle savedInstanceState) { 
    		super.onCreate(savedInstanceState);
    		setContentView(R.layout.activity_main);
    	}
    
    	public void downloadApk(View v) { 
    		new AsyncTask<Void, Integer, Void>(){ 
    			
    			//1. 主线程, 显示提示视图
    			@Override
    			protected void onPreExecute() { 
    				dialog = new ProgressDialog(MainActivity.this);
    				dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
    				dialog.show();
    				apkFile = new File(getExternalFilesDir(null), "update.apk");
    			}
    
    			
    			
    			//3. 主线程, 更新界面
    			@Override
    			protected void onPostExecute(Void result) { 
    				dialog.dismiss();
    				installAPK();
    			}
    			
    			//2. 分线程, 联网请求
    			@Override
    			protected Void doInBackground(Void... params) { 
    				try { 
    					//1. 得到连接对象
    					String path = "http://192.168.1.14:8080/Web_Server/L04_DataStorage.apk";
    					URL url = new URL(path);
    					HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    					//2. 设置
    					//connection.setRequestMethod("GET");
    					connection.setConnectTimeout(5000);
    					connection.setReadTimeout(10000);
    					//3. 连接
    					connection.connect();
    					//4. 请求并得到响应码200
    					int responseCode = connection.getResponseCode();
    					if(responseCode==200) { 
    						//设置dialog的最大进度
    						dialog.setMax(connection.getContentLength());
    						
    						
    						//5. 得到包含APK文件数据的InputStream
    						InputStream is = connection.getInputStream();
    						//6. 创建指向apkFile的FileOutputStream
    						FileOutputStream fos = new FileOutputStream(apkFile);
    						//7. 边读边写
    						byte[] buffer = new byte[1024];
    						int len = -1;
    						while((len=is.read(buffer))!=-1) { 
    							fos.write(buffer, 0, len);
    							//8. 显示下载进度
    							//dialog.incrementProgressBy(len);
    							//在分线程中, 发布当前进度
    							
    							publishProgress(len);
    							
    							//休息一会(模拟网速慢)
    							//Thread.sleep(50);
    							SystemClock.sleep(50);
    						}
    						
    						fos.close();
    						is.close();
    					}
    					//9. 下载完成, 关闭, 进入3)
    					connection.disconnect();
    				} catch (Exception e) { 
    					e.printStackTrace();
    				}
    				return null;
    			}
    			//在主线程中更新进度(在publishProgress()之后)
    			protected  void onProgressUpdate(Integer[] values) { 
    				dialog.incrementProgressBy(values[0]);
    			};
    		}.execute();
    	}
    
    	/** * 启动安装APK */
    	private void installAPK() { 
    		Intent intent = new Intent("android.intent.action.INSTALL_PACKAGE");
    		intent.setDataAndType(Uri.fromFile(apkFile), "application/vnd.android.package-archive");
    		startActivity(intent);
    	}
    }

学习android中的异步任务，我们需要掌握如下几个API  
新建AsyncTask有三个泛型public abstract class AsyncTask<Params, Progress, Result>  
根据实际情况传递，空的话，传Void  
在项目中需要了解异步任务线程的调用关系，顺序  
protected void onPreExecute() \{// 调用execute()方法前，一般显示提示视图

protected void onPostExecute(Void result)// 调用execute()之后，一般是做一下UI更新操作

protected Void doInBackground(Void… params)// 分线程去执行联网相关请求

protected final void publishProgress(Progress… values) // 在doInBackground方法中发布进度，这个会触发protected void onProgressUpdate(Integer\[\] values) 方法  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h1YW5nYmFva2FuZw_size_16_color_FFFFFF_t_70]

[Link 1]: https://www.captainai.net/flyop007/
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