Outline

• HTTP and Android
• Quiz
• iPhone Networking

HTTP

• Last day, we saw how to use Android to send and receive data over a Socket connection.
• One of the most common protocols implemented on top of TCP sockets is HTTP, the hypertext transfer protocol.
• It is what is used to get web pages from a web server.
• Today we begin by look at what facilities Android has for requesting web pages.

WebView

• The easiest way to just view a web-page in Android is to:
  • Add the line:

     <uses-permission android:name="android.permission.INTERNET"></uses-permission>     
    

    to the manifest file
  • Add a WebView to our layout:

    <WebView  
        android:id="@+id/webview"
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        />
    

  • Set the web page of the view in onCreate. (Need to import package android.webkit.*) :

    webview = (WebView) findViewById(R.id.webview);
    webview.getSettings().setJavaScriptEnabled(true);
    webview.loadUrl("http://www.pollett.org/");
    

  • It should be noted that both the browsers in Android and iPhone are built off of webkit.

More on WebView

• By default, links clicked on out of our WebView will be handled by the Android web browser.
• To handle them ourselves, we could write a subclass of WebViewClient and override shouldOverrideUrlLoading:

  private class MyWebViewClient extends WebViewClient {
      @Override
      public boolean shouldOverrideUrlLoading(WebView view, String url) {
          view.loadUrl(url);
          return true;
      }
  }
  

• Then we set the WebViewClient of our WebView with a line like:

  webview.setWebViewClient(new MyWebViewClient());
  

A Lower Level Way to Request a Page

• One common reason to use HTTP is make use of a web service.
• One might make a request of the form:

  URL/service_name/method_name/?arg1=value1&arg2=value2...
  

  which requests from the given URL the given method of the given web service with the given arguments.
• The response is typically an XML or JSON document which is the output of calling the method.
• We typically want to use data from this document, but we don't want to display it in a WebView.
• This calls for a lower level way of dealing with the web.

Request a Page Using java.net

• Using java.net, we could write code like:

  String location="URL/service_name/method_name/?arg1=value1&arg2=value2";
  String result = null;
  try {
     url = new URL(location);
  } catch (MalformedURLException e) {
    //handle somehow
  }
  if(url != null) {
     try {
        HttpURLConnection urlConn =
           (HttpURLConnection) url.openConnection();
  
        BufferedReader in =
           new BufferedReader(
              new InputStreamReader(
                 urlConn.getInputStream()));
        String inputLine;
        while((inputLine = in.readLine()) != null)
        {
           result += "\n" + inputLine;
        }
     }
     catch (IOException e) {
     // handle somehow
     }
  
     return result;
  }
  return null;
  
  

Quiz

Networking on the iPhone

• The iPhone analog of WebView is UIWebView.
• You could drag and drop this into a view using Interface Builder.
• But since we haven't done UI stuff programmatically yet, let's consider how we could do it.
• Create a new window-based application then modify the delegate:

  - (void)applicationDidFinishLaunching:(UIApplication *)application {    
  
      // Override point for customization after application launch
      [window makeKeyAndVisible];
  
  	CGRect bounds = [[UIScreen mainScreen ] applicationFrame];
  	UIWebView *webView = [[UIWebView alloc] initWithFrame:bounds];
  	webView.scalesPageToFit = YES;
  		
      [window addSubview:webView];
  	
  	NSURL *url = [NSURL URLWithString:@"http://www.pollett.org"];
  	NSURLRequest *request = [NSURLRequest requestWithURL:url];
  	[webView loadRequest:request];
  }
  

Some UIWebView and UiWebViewDelegate methods

• A UIWebView object manages browser history and you can use these to control browsing programmatically with calls like: [webView goBack]; [webView goForward]; [webView reload]; [webView stopLoading];
• The web view class also supports a set of delegate methods which will be called automatically when certain events occur.
• To set the handler for this methods you could create a subclass of UIWebViewDelegate and then set it with the command:

  webView.delegate = myDelegate;
  

• Here are some of the messages you can override:
  • -(BOOL)webView:(UIWebView *)webView, shouldStartLoadWithRequest:(NSURLRequest *)request, navigationType:(UIWebViewNavigationType)navigationType; -- this is called when the web view is instructed to load content. It should return YES to commence loading. The possible navigationType parameters are: UIWebViewNavigationTypeLinkClicked, UIWebViewNavigationTypeFormSubmitted, UIWebViewNavigationTypeBackForward, UIWebViewNavigationTypeReload, UIWebViewNavigationTypeFormResubmitted, UIWebViewNavigationTypeOther.
  • -(void)webViewDidStartLoad:(UIWebView)webView; -- notified when the web view begins loading a request
  • -(void)webViewDidFinishLoad:(UIWebView)webView; -- notified when the web view finishes loading a request
  • -(void)webView:(UIWebView *)webView, didFailLoadWithError:(NSError *)error -- Notified if an error occurs in the loading of a request

Getting the Response into Data

• So what if we want a quick and dirty way to get the response of a web service?
• We can do:

  NSData *myData = [NSData dataWithContentsOfURL: [NSURL URLWithString: @"http://web_service_url"]];
  

• Many objects actually have a way to directly use an NSData object. For instance, if the response was an image we could do:

  UIImage *image = [UIImage imageWithData: myData]; 
  

• To get a string out of myData for parsing we could do:

  NSString *string = [NSString stringWithFormat:@"%.*s", [myData length], [myData bytes]];