我正在熟悉 Android 框架和 Java，并想创建一个通用的“NetworkHelper”类，它可以处理大部分网络代码，使我能够从中调用网页。
我按照 developer.android.com 上的这篇文章创建了我的网络类：http: //developer.android.com/training/basics/network-ops/connecting.html
代码：
package com.example.androidapp;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.util.Log;
/**
* @author tuomas
* This class provides basic helper functions and features for network communication.
*/
public class NetworkHelper
{
private Context mContext;
public NetworkHelper(Context mContext)
{
//get context
this.mContext = mContext;
}
/**
* Checks if the network connection is available.
*/
public boolean checkConnection()
{
//checks if the network connection exists and works as should be
ConnectivityManager connMgr = (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected())
{
//network connection works
Log.v("log", "Network connection works");
return true;
}
else
{
//network connection won't work
Log.v("log", "Network connection won't work");
return false;
}
}
public void downloadUrl(String stringUrl)
{
new DownloadWebpageTask().execute(stringUrl);
}
//actual code to handle download
private class DownloadWebpageTask extends AsyncTask<String, Void, String>
{
@Override
protected String doInBackground(String... urls)
{
// params comes from the execute() call: params[0] is the url.
try {
return downloadUrl(urls[0]);
} catch (IOException e) {
return "Unable to retrieve web page. URL may be invalid.";
}
}
// Given a URL, establishes an HttpUrlConnection and retrieves
// the web page content as a InputStream, which it returns as
// a string.
private String downloadUrl(String myurl) throws IOException
{
InputStream is = null;
// Only display the first 500 characters of the retrieved
// web page content.
int len = 500;
try {
URL url = new URL(myurl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000 );
conn.setConnectTimeout(15000);
conn.setRequestMethod("GET");
conn.setDoInput(true);
// Starts the query
conn.connect();
int response = conn.getResponseCode();
Log.d("log", "The response is: " + response);
is = conn.getInputStream();
// Convert the InputStream into a string
String contentAsString = readIt(is, len);
return contentAsString;
// Makes sure that the InputStream is closed after the app is
// finished using it.
} finally {
if (is != null) {
is.close();
}
}
}
// Reads an InputStream and converts it to a String.
public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException
{
Reader reader = null;
reader = new InputStreamReader(stream, "UTF-8");
char[] buffer = new char[len];
reader.read(buffer);
return new String(buffer);
}
// onPostExecute displays the results of the AsyncTask.
@Override
protected void onPostExecute(String result)
{
//textView.setText(result);
Log.v("log", result);
}
}
}
在我的活动课程中，我以这种方式使用该课程：
connHelper = new NetworkHelper(this);
...
if (connHelper.checkConnection())
{
//connection ok, download the webpage from provided url
connHelper.downloadUrl(stringUrl);
}
我遇到的问题是我应该以某种方式对活动进行回调，并且它应该可以在“downloadUrl()”函数中定义。例如，当下载完成时，Activity 中的 public void "handleWebpage(String data)" 函数会以加载的字符串作为参数被调用。
我做了一些谷歌搜索，发现我应该以某种方式使用接口来实现这个功能。在查看了几个类似的 stackoverflow 问题/答案后，我没有得到它的工作，我不确定我是否正确理解了接口：如何在 Java 中将方法作为参数传递？老实说，使用匿名类对我来说是新的，我不确定我应该在哪里或如何在提到的线程中应用示例代码片段。
所以我的问题是如何将回调函数传递给我的网络类并在下载完成后调用它？接口声明去哪里，实现关键字等等？请注意，我是 Java 的初学者（虽然有其他编程背景），所以我会很感激你的解释:) 谢谢！