📌  相关文章
📜  Android-网络连接

📅  最后修改于: 2021-01-05 05:24:51             🧑  作者: Mango

Android使您的应用程序连接到Internet或任何其他本地网络，并允许您执行网络操作。

设备可以具有各种类型的网络连接。本章重点介绍使用Wi-Fi或移动网络连接。

检查网络连接

在执行任何网络操作之前，必须首先检查是否已连接到该网络或Internet等。为此android提供ConnectivityManager类。您需要通过调用getSystemService()方法来实例化此类的对象。其语法如下-

ConnectivityManager check = (ConnectivityManager) 
this.context.getSystemService(Context.CONNECTIVITY_SERVICE);

实例化ConnectivityManager类的对象后，就可以使用getAllNetworkInfo方法获取所有网络的信息。此方法返回NetworkInfo数组。因此，您必须像这样接收它。

NetworkInfo[] info = check.getAllNetworkInfo();

您需要做的最后一件事是检查网络的连接状态。其语法如下-

for (int i = 0; i

除了这些连接状态之外，网络还可以实现其他状态。它们在下面列出-

Sr.No State
1 Connecting
2 Disconnected
3 Disconnecting
4 Suspended
5 Unknown

执行网络操作

检查您已连接到Internet后，您可以执行任何网络操作。在这里，我们从网址中获取网站的html。

Android提供HttpURLConnection和URL类来处理这些操作。您需要通过提供网站链接来实例化URL类的对象。它的语法如下-

String link = "http://www.google.com";
URL url = new URL(link);

之后，您需要调用url类的openConnection方法并将其接收到HttpURLConnection对象中。之后，您需要调用HttpURLConnection类的connect方法。

HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.connect();

最后，您需要做的就是从网站获取HTML。为此，您将使用InputStream和BufferedReader类。其语法如下-

InputStream is = conn.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
String webPage = "",data="";

while ((data = reader.readLine()) != null){
   webPage += data + "\n";
}

除了此connect方法之外，HttpURLConnection类中还有其他可用的方法。它们在下面列出-

Sr.No Method & description
1

disconnect()

This method releases this connection so that its resources may be either reused or closed
2

getRequestMethod()

This method returns the request method which will be used to make the request to the remote HTTP server
3

getResponseCode()

This method returns response code returned by the remote HTTP server
4

setRequestMethod(String method)

This method Sets the request command which will be sent to the remote HTTP server
5

usingProxy()

This method returns whether this connection uses a proxy server or not

例

下面的示例演示HttpURLConnection类的用法。它创建一个基本的应用程序，使您可以从给定的网页下载HTML。

要尝试使用此示例，您需要在连接了wifi互联网的实际设备上运行该示例。

Steps Description
1 You will use Android studio IDE to create an Android application under a package com.tutorialspoint.myapplication.
2 Modify src/MainActivity.java file to add Activity code.
4 Modify layout XML file res/layout/activity_main.xml add any GUI component if required.
6 Modify AndroidManifest.xml to add necessary permissions.
7 Run the application and choose a running android device and install the application on it and verify the results.

这是src / MainActivity.java的内容。

package com.tutorialspoint.myapplication;

import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

import android.net.ConnectivityManager;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.ActionBarActivity;
import android.view.View;

import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.IOException;
import java.io.InputStream;

import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;

public class MainActivity extends ActionBarActivity {
   private ProgressDialog progressDialog;
   private Bitmap bitmap = null;
   Button b1;

   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      b1 = (Button) findViewById(R.id.button);

      b1.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            checkInternetConenction();
            downloadImage("http://www.tutorialspoint.com/green/images/logo.png");
         }
      });
   }

   private void downloadImage(String urlStr) {
      progressDialog = ProgressDialog.show(this, "", "Downloading Image from " + urlStr);
      final String url = urlStr;

      new Thread() {
         public void run() {
            InputStream in = null;

            Message msg = Message.obtain();
            msg.what = 1;

            try {
               in = openHttpConnection(url);
               bitmap = BitmapFactory.decodeStream(in);
               Bundle b = new Bundle();
               b.putParcelable("bitmap", bitmap);
               msg.setData(b);
               in.close();
            }catch (IOException e1) {
               e1.printStackTrace();
            }
            messageHandler.sendMessage(msg);
         }
      }.start();
   }

   private InputStream openHttpConnection(String urlStr) {
      InputStream in = null;
      int resCode = -1;

      try {
         URL url = new URL(urlStr);
         URLConnection urlConn = url.openConnection();

         if (!(urlConn instanceof HttpURLConnection)) {
            throw new IOException("URL is not an Http URL");
         }
            
         HttpURLConnection httpConn = (HttpURLConnection) urlConn;
         httpConn.setAllowUserInteraction(false);
         httpConn.setInstanceFollowRedirects(true);
         httpConn.setRequestMethod("GET");
         httpConn.connect();
         resCode = httpConn.getResponseCode();

         if (resCode == HttpURLConnection.HTTP_OK) {
            in = httpConn.getInputStream();
         }
      }catch (MalformedURLException e) {
         e.printStackTrace();
      }catch (IOException e) {
         e.printStackTrace();
      }
      return in;
   }

   private Handler messageHandler = new Handler() {
      public void handleMessage(Message msg) {
         super.handleMessage(msg);
         ImageView img = (ImageView) findViewById(R.id.imageView);
         img.setImageBitmap((Bitmap) (msg.getData().getParcelable("bitmap")));
         progressDialog.dismiss();
      }
   };

   private boolean checkInternetConenction() {
      // get Connectivity Manager object to check connection
      ConnectivityManager connec
         =(ConnectivityManager)getSystemService(getBaseContext().CONNECTIVITY_SERVICE);

      // Check for network connections
      if ( connec.getNetworkInfo(0).getState() == 
         android.net.NetworkInfo.State.CONNECTED ||
         connec.getNetworkInfo(0).getState() == 
         android.net.NetworkInfo.State.CONNECTING ||
         connec.getNetworkInfo(1).getState() == 
         android.net.NetworkInfo.State.CONNECTING ||
         connec.getNetworkInfo(1).getState() == android.net.NetworkInfo.State.CONNECTED ) {
            Toast.makeText(this, " Connected ", Toast.LENGTH_LONG).show();
            return true;
         }else if (
            connec.getNetworkInfo(0).getState() == 
            android.net.NetworkInfo.State.DISCONNECTED ||
            connec.getNetworkInfo(1).getState() == 
            android.net.NetworkInfo.State.DISCONNECTED  ) {
               Toast.makeText(this, " Not Connected ", Toast.LENGTH_LONG).show();
               return false;
            }
         return false;
   }

}

这是activity_main.xml的内容。

这是Strings.xml的内容。


   My Application

这是AndroidManifest.xml的内容

让我们尝试运行您的应用程序。我假设您已将实际的Android Mobile设备与计算机连接。要从android studio运行该应用，请打开您项目的活动文件之一，然后点击运行Eclipse运行图标工具栏中的图标。在启动应用程序之前，Android Studio将显示以下窗口，以选择要在其中运行Android应用程序的选项。

Anroid网络连接教程

选择您的移动设备作为选项，然后检查将显示以下屏幕的移动设备-

Anroid网络连接教程

现在只需单击按钮，它将检查互联网连接以及下载图像。

Anroid网络连接教程

出来如下，它已经从互联网上获取了徽标。

Anroid网络连接教程