AsyncTask的使用

超、凢脫俗 2024-02-17 14:05 40阅读 0赞

package com.example.asynctask;
    
    import android.os.AsyncTask;
    import android.os.Bundle;
    import android.app.Activity;
    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.view.Menu;
    import android.view.View;
    import android.widget.ImageView;
    import android.widget.ProgressBar;
    
    public class MainActivity extends Activity {
    	private AsyncImageLoader loader;
    	
    	private ImageView iv;
    	
    	private ProgressBar bar;
    
    	@Override
    	protected void onCreate(Bundle savedInstanceState) {
    		super.onCreate(savedInstanceState);
    		setContentView(R.layout.activity_main);
    		initView();
    		
    		loader = new AsyncImageLoader();
    		//传入的参数类型由定义类时的第一个type类型确定
    		loader.execute(R.drawable.a);
    	}
    	
    	private void initView() {
    		iv = (ImageView) findViewById(R.id.image_view);
    		bar = (ProgressBar) findViewById(R.id.progress_bar);
    		
    	}
    
    	@Override
    	public boolean onCreateOptionsMenu(Menu menu) {
    		getMenuInflater().inflate(R.menu.main, menu);
    		return true;
    	}
    	
    	/**
    	 * @author Administrator
    	 * AsyncTask可以直接修改UI，内置handler
    	 * 三种类型的含义：
    	 * Params, the type of the parameters sent to the task upon execution. 
         * Progress, the type of the progress units published during the background computation. 
         * Result, the type of the result of the background computation. 
    	 */
    	private class AsyncImageLoader extends AsyncTask<Integer, Integer, Bitmap> {
    		
    		@Override
    		protected void onPreExecute() {
    			bar.setMax(20);
    			bar.setVisibility(View.VISIBLE);
    		}
    
    		@Override
    		protected Bitmap doInBackground(Integer... params) {
    			for(int i=1; i<=20; i++) {
    				publishProgress(i);//会调用onProgressUpdate方法
    				try {
    					new Thread().sleep(500);
    				} catch (InterruptedException e) {
    					e.printStackTrace();
    				}
    				if(i == 16)
    					//用于取消加载
    					cancel(true);
    			}
    			if(isCancelled()) 
    				return null;
    			return BitmapFactory.decodeResource(getResources(), params[0]);
    		}
    		
    		@Override
    		protected void onProgressUpdate(Integer... values) {
    			bar.setProgress(values[0]);
    		}
    		
    		@Override
    		protected void onPostExecute(Bitmap result) {
    			//result即为doInBackground的返回值
    			bar.setVisibility(View.GONE);
    			iv.setImageBitmap(result);
    		}
    	}
     
    }

用AsyncTask获取网络数据，源码：

package com.example.asynctask;
    
    import java.io.BufferedInputStream;
    import java.io.BufferedReader;
    import java.io.ByteArrayInputStream;
    import java.io.ByteArrayOutputStream;
    import java.io.File;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.io.PrintWriter;
    import java.io.RandomAccessFile;
    import java.io.Reader;
    import java.io.Writer;
    import java.net.HttpURLConnection;
    import java.net.MalformedURLException;
    import java.net.URL;
    import java.net.URLConnection;
    
    import android.net.ConnectivityManager;
    import android.net.NetworkInfo;
    import android.net.Uri;
    import android.os.AsyncTask;
    import android.os.Bundle;
    import android.os.Environment;
    import android.app.Activity;
    import android.content.BroadcastReceiver;
    import android.content.Context;
    import android.content.Intent;
    import android.content.IntentFilter;
    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.view.Menu;
    import android.view.View;
    import android.widget.ImageView;
    import android.widget.ProgressBar;
    import android.widget.TextView;
    
    public class MainActivity extends Activity {
    	//自定义异步加载类
    	private AsyncImageLoader loader;
    	
    	private ImageView iv;
    	private ProgressBar bar;
    	private TextView tv;
    	//网络连接的manager
    	private ConnectivityManager manager;
    
    	@Override
    	protected void onCreate(Bundle savedInstanceState) {
    		super.onCreate(savedInstanceState);
    		setContentView(R.layout.activity_main);
    		initView();
    		netCheck();
    		networkChange();
    		
    		String url = "http://www.dm123.cn/ecms/d/file/2013-09-16/6615d9c9513c89d2e156908fb0b3193b.jpg";
    		loader = new AsyncImageLoader();
    			//传入的参数类型由定义类时的第一个type类型确定
    		loader.execute(url);
    	}
    	//初始化view
    	private void initView() {
    		iv = (ImageView) findViewById(R.id.image_view);
    		bar = (ProgressBar) findViewById(R.id.progress_bar);
    		tv = (TextView) findViewById(R.id.text_view);
    	}
    	//检查网络状态
    	private void netCheck() {
    		manager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
    		NetworkInfo[] networkInfos = manager.getAllNetworkInfo();
    		for(NetworkInfo network : networkInfos) {
    			System.out.println("the name of the network type: " + network.getTypeName());
    			//在每次用网络传输东西时都应该先检查网络是否连接
    			System.out.println("whether network connectivity exists: " + network.isConnected());
    			System.out.println("whether network connectivity is possible: " + network.isAvailable());
    		}
    	}
    	//当网络状态发生改变时，用receiver接收
    	private void networkChange() {
    		BroadcastReceiver receiver = new BroadcastReceiver() {
    			
    			@Override
    			public void onReceive(Context context, Intent intent) {
    				NetworkInfo mobile = manager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
    				NetworkInfo wifi = manager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
    				if(mobile.isAvailable() && mobile.isConnected()) {
    					System.out.println("Mobile可用且已连接");
    				} else if(wifi.isAvailable() && wifi.isConnected()) {
    					System.out.println("WiFi可用且已连接");
    				} else {
    					System.out.println("网络不可用");
    				}
    			}
    		};
    		IntentFilter filter = new IntentFilter();
    		filter.addAction(ConnectivityManager.CONNECTIVITY_ACTION);
    		//注册receiver，当网络状态发生改变时，系统会发出广播
    		registerReceiver(receiver, filter);
    	}
    
    	@Override
    	public boolean onCreateOptionsMenu(Menu menu) {
    		getMenuInflater().inflate(R.menu.main, menu);
    		return true;
    	}
    	
    	/**
    	 * @author Administrator
    	 * AsyncTask可以直接修改UI，内置handler
    	 * 三种类型的含义：
    	 * Params, the type of the parameters sent to the task upon execution. 
         * Progress, the type of the progress units published during the background computation. 
         * Result, the type of the result of the background computation. 
    	 */
    	private class AsyncImageLoader extends AsyncTask<String, Integer, Bitmap> {
    		
    		@Override
    		protected void onPreExecute() {
    			bar.setVisibility(View.VISIBLE);
    		}
    
    		@Override
    		protected Bitmap doInBackground(String... params) {
    			URL url = null;
    			try {
    				url = new URL(params[0]);
    			} catch (MalformedURLException e) {
    				e.printStackTrace();
    			}
    			return readBitmap(url);
    		}
    		
    		@Override
    		protected void onProgressUpdate(Integer... values) {
    			bar.setProgress(values[0]);
    		}
    		
    		@Override
    		protected void onPostExecute(Bitmap result) {
    			bar.setVisibility(View.GONE);
    			iv.setImageBitmap(result);
    		}
    		//读取图片
    		private Bitmap readBitmap(URL url) {
    			Bitmap bitmap = null;
    			int fileLength = 0, doneLength = 0;
    			try {
    				HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    				//设置连接超时
    				conn.setConnectTimeout(10000);
    				//设置读取超时
    				conn.setReadTimeout(150000);
    				//设置连接方式
    				conn.setRequestMethod("GET");
    				System.out.println("请求码： " + conn.getResponseCode());
    				//根据请求码判断是否连接成功
    				if(!(conn.getResponseCode() == HttpURLConnection.HTTP_OK)) {
    					//如果不成功则加载一个本地图片
    					bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
    					return bitmap;
    				}
    				//把网页文件内容的字节流转换成字符流
    				InputStream is = conn.getInputStream();
    				//ByteArrayOutputStream是把内容读到一个byte数组里（即存储到内存中）
    				//而ByteArrayInputStream是从一个数组里读取内容，返回所读取的值或者读取到一个数组里，
    				//返回读取的长度
    				ByteArrayOutputStream bos = new ByteArrayOutputStream();
    				//得到文件长度
    				fileLength = conn.getContentLength();
    				bar.setMax(fileLength);
    				byte[] buf = new byte[1024 * 1024];
    				int len = 0;
    				//记录读取的次数
    				int num = 0;
    				while((len = is.read(buf)) != -1) {
    					bos.write(buf, 0, len);
    					doneLength +=len;
    					publishProgress(doneLength);
    					num ++;
    				}
    				System.out.println("读取的次数" + num);
    				ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
    //				byte[] data = bos.toByteArray();
    //				System.out.println(data.length);
    //				bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);
    				bitmap = BitmapFactory.decodeStream(bis);
    				is.close();
    			} catch (IOException e) {
    				System.out.println("网络连接失败！");
    				e.printStackTrace();
    			}
    			return bitmap;
    		}
    		//读取html文件
    		private String readHtml(URL url) {
    			File file = new File(Environment.getExternalStorageDirectory(), "net.html");
    			if(!file.exists()) {
    				try {
    					file.createNewFile();
    				} catch (IOException e) {
    					System.out.println("文件创建失败");
    					e.printStackTrace();
    				}
    			}
    			StringBuilder builder = new StringBuilder();
    			int fileLength = 0, doneLength = 0;
    			try {
    //				Writer writer = new PrintWriter(new FileOutputStream(file));
    				HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    				//设置连接超时
    				conn.setConnectTimeout(10000);
    				//设置读取超时
    				conn.setReadTimeout(150000);
    				//设置连接方式
    				conn.setRequestMethod("GET");
    				System.out.println("请求码： " + conn.getResponseCode());
    				//把网页文件内容的字节流转换成字符流
    				Reader reader = new InputStreamReader(conn.getInputStream());
    				fileLength = conn.getContentLength();
    				bar.setMax(fileLength);
    				char[] buf = new char[1024 * 1024];
    				int len = 0;
    				while((len = reader.read(buf)) != -1) {
    //					writer.write(buf, 0, len);
    					builder.append(buf);
    					doneLength +=len;
    					publishProgress(doneLength);
    				}
    				reader.close();
    //				writer.close();
    			} catch (IOException e) {
    				System.out.println("网络连接失败！");
    				e.printStackTrace();
    			}
    			return builder.toString();
    		}
    	}
     
    }
     
    
     
    
    
    网络连接首先要判断有哪些网络可用，然后监听网络状态
     
     网络数据传输用HttpURLConnection，设置各种参数，之后接可以读取网页内容并存储或者展现在UI上 
     读取的时候，如果是网页则直接用字符流，不用自己再转换流了，如果是图片等用字节流，读取完后转化成相应的类型，（Bitmap可直接接受io流）