Phát triển ứng dụng cho iPhone và iPad - part 37 docx

Next, you defi ne an MKCoordinateRegion struct. You will pass this struct to the mapView to defi ne the region that you want to display. An MKCoordinateRegion consists of a span and a center point. You will center the map on the coordinate that you receive from Core Location. Next, you tell the mapView to set the region displayed on the map and to animate the transition to your new region. Finally, you tell the Core Location manager to stop getting location updates from the GPS. Because your application does not need extremely accurate resolution, nor do you need constant updates from the GPS, you can conserve power by turning the GPS off. For the next step, you need to make a couple of additions to the viewDidLoad method. Because you will be customizing the pin colors for your annotations, you need to set the mapView delegate to self . In addition, for illustrative purposes, you will display the user ’ s location on the map by setting the map view ’ s showsUserLocation property to YES . When using the showsUserLocation property, you need to be aware that this will cause the map view to use Core Location to retrieve and maintain the user ’ s location on the map. This forces the GPS receiver to remain on, consuming valuable battery power. You should carefully consider if your application needs this functionality or not before using it. This example uses this feature to demonstrate a capability of the map view to display the user ’ s current location. Here is the complete implementation of viewDidLoad : - (void)viewDidLoad { [super viewDidLoad]; // Create the results array self.results = [[NSMutableArray alloc] init]; // Create the Core Location CLLocationManager CLLocationManager *locationManager = [[CLLocationManager alloc] init]; // Set the delegate to self [locationManager setDelegate:self]; // Tell the location manager to start updating the location [locationManager startUpdatingLocation]; // Set the delegate for the searchbar [self.searchBar setDelegate:self]; // Set the delegate for the mapView [self.mapView setDelegate:self]; // Use Core Location to find the user’s location and display it on the map // Be careful when using this because it causes the mapview to continue to // use Core Location to keep the user’s position on the map up to date self.mapView.showsUserLocation = YES; } LocationSearchViewController.m Example 1: Location - Based Search ❘ 329 CH011.indd 329CH011.indd 329 9/18/10 10:05:10 AM9/18/10 10:05:10 AM 330 ❘ CHAPTER 11 INTEGRATING WITH WEB SERVICES When the user clears the text from the search bar, you want to clear the old annotations from the map. You can do this by implementing the searchBar:textDidChange: delegate method like this: // Called when the searchbar text changes - (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText{ NSLog (@”textDidChange”); // If the text was cleared, clear the map annotations if ([searchText isEqualToString:@””]) { // Clear the annotations [self.mapView removeAnnotations:self.mapView.annotations]; // Clear the results array [self.results removeAllObjects]; } } LocationSearchViewController.m You implement this code to check to see if the user has cleared the search string. If he has, you remove the annotations from the map and clear your results array. In the last bit of code, you will implement the mapView:viewForAnnotation: delegate method. The map view will call this method when the map needs the view for an annotation. If you wanted to implement a custom view for your annotations, you would do it in this method. Instead of implementing a custom view, you will use the MKPinAnnotationView ; however, you could easily replace this with your own view. You will change the color of the pin based on the user rating of the business that you are plotting on the map. Here is the code: - (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id < MKAnnotation > )annotation { // If we are displaying the user’s location, return nil // to use the default view if ([annotation isKindOfClass:[MKUserLocation class]]) { return nil; } // Try to dequeue an existing pin MKPinAnnotationView *pinAnnotationView = (MKPinAnnotationView *) [self.mapView dequeueReusableAnnotationViewWithIdentifier:@”location”]; if (!pinAnnotationView) { // We could not get a pin from the queue pinAnnotationView=[[[MKPinAnnotationView alloc] initWithAnnotation:annotation CH011.indd 330CH011.indd 330 9/18/10 10:05:11 AM9/18/10 10:05:11 AM reuseIdentifier:@”location”] autorelease]; pinAnnotationView.animatesDrop=TRUE; pinAnnotationView.canShowCallout = YES; } // We need to get the rating from the annotation object // to color the pin based on rating Result *resultAnnotation = (Result*) annotation; if (resultAnnotation.rating > 4.5) { pinAnnotationView.pinColor = MKPinAnnotationColorGreen; } else if (resultAnnotation.rating > 3.5) { pinAnnotationView.pinColor = MKPinAnnotationColorPurple; } else { pinAnnotationView.pinColor = MKPinAnnotationColorRed; } return pinAnnotationView; } LocationSearchViewController.m The fi rst line of the method checks to see if the annotation is for the user location view. If it is, you simply return nil to tell the map to use the default annotation. Next, you will see the attempt to dequeue an existing annotation view. The MapView works very much like the TableView in this respect. It doesn ’ t make sense to keep invisible map annotations in memory. Therefore, the MapView creates and releases annotations as they become visible or disappear from the map respectively. Instead of creating new annotation instances every time, the MapView maintains an internal queue of annotation objects that it can reuse. Therefore, you fi rst try to dequeue an annotation. If you cannot, you create a new pin annotation view with the correct reuse identifi er. Then, you set the attributes of this view. Next, you cast the annotation that the MapView is asking for to a Result object. Then, you use the rating property of the Result to set the color of the pin. Finally, you return the pinAnnotationView . Finishing Up The code is now complete. You should be able to successfully build and run the application. If you attempt to run the application in the simulator, you will see that the device thinks that it is at Apple headquarters, regardless of where you are actually located. This is by design. Enter a search term in the search bar and watch the pins drop to show you the results. You can view the XML returned by the web service in the console. Example 1: Location - Based Search ❘ 331 CH011.indd 331CH011.indd 331 9/18/10 10:05:11 AM9/18/10 10:05:11 AM 332 ❘ CHAPTER 11 INTEGRATING WITH WEB SERVICES EXAMPLE 2: TERM EXTRACTION When making calls to a web service, you will often use the HTTP GET method to send parameters to the service. When dealing with REST - based web services, you use GET to indicate that you are performing a query for some data from the server. There are occasions where you will need to POST data to the server. Many SOAP - based web services use POST to send data. REST uses the POST method to indicate that you are sending data to the server and intend to modify the database. Sending a POST request is very similar to sending a GET request with some minor exceptions, as you will see in the example code. In this example, you will make a call to the Yahoo! Term Extraction service. This service returns a list of what it deems to be the signifi cant words and phrases in the text passage that you submit. There is no defi nition of what Yahoo! determines to be “ signifi cant, ” nor is their algorithm to determine signifi cance public. Because of the length of the string that you can submit to the service, it is not practical to use the GET method; therefore, the service requires that you use POST to send your string into the web service. You can apply the same principles that you use here to any web service that requires you to submit data using the POST method. The completed example will look like Figure 11 - 5. Getting Started To get started, open Xcode and create a new View - based application called TermExtract. In the TermExtractViewController.h header fi le, add instance variables for two UITextView variables: UITextView *textToExtractTextView; UITextView *extractedTermsTextView; Next, add properties for these UITextView s: @property (nonatomic, retain) IBOutlet UITextView *textToExtractTextView; @property (nonatomic, retain) IBOutlet UITextView *extractedTermsTextView; Also, add instance variables for the response data that you will receive from the server in response to your request, and the characters that you will capture during XML parsing: NSMutableData *responseData; NSMutableString *capturedCharacters; Now, add a property for the responseData : @property (nonatomic, retain) NSMutableData *responseData; FIGURE 11 - 5: Complete term extraction application CH011.indd 332CH011.indd 332 9/18/10 10:05:12 AM9/18/10 10:05:12 AM Next, add an IBAction method called extractTerms that you will call after the user enters the text to send to the service. Finally, add an instance method called parseXML that you will invoke to start the XML processing: - (IBAction) extractTerms:(id)sender; - (void) parseXML; The complete header should look like this: #import < UIKit/UIKit.h > @interface TermExtractViewController : UIViewController { UITextView *textToExtractTextView; UITextView *extractedTermsTextView; NSMutableData *responseData; NSMutableString *capturedCharacters; } @property (nonatomic, retain) IBOutlet UITextView *textToExtractTextView; @property (nonatomic, retain) IBOutlet UITextView *extractedTermsTextView; @property (nonatomic, retain) NSMutableData *responseData; - (IBAction) extractTerms:(id)sender; - (void) parseXML; @end TermExtractViewController.h In the implementation fi le, synthesize the textToExtractTextView,extractedTermsTextView, responseData properties: @synthesize textToExtractTextView,extractedTermsTextView,responseData; Then, add the code to clean up the properties in the viewDidUnload method: - (void)viewDidUnload { // Release any retained subviews of the main view. // e.g. self.myOutlet = nil; self.textToExtractTextView=nil; self.extractedTermsTextView=nil; self.responseData=nil; } TermExtractViewController.m Example 2: Term Extraction ❘ 333 CH011.indd 333CH011.indd 333 9/18/10 10:05:13 AM9/18/10 10:05:13 AM 334 ❘ CHAPTER 11 INTEGRATING WITH WEB SERVICES Finally, release your instance variables and call the superclass ’ s dealloc method in dealloc : - (void)dealloc { [textToExtractTextView release]; [extractedTermsTextView release]; [responseData release]; [super dealloc]; } TermExtractViewController.m Building the User Interface You will now build the user interface for the application using Interface Builder. Double - click on the TermExtractViewController.xib fi le in Xcode to open the fi le in Interface Builder. Once the interface view is open, add two UITextView s, two UILabel s, and a UIButton , as shown in Figure 11 - 6. Change the title attribute of the UIButton to read “ Extract Terms. ” Change the text of the top UILabel to read “ Text to extract: ” and the bottom UILabel to “ Extracted Terms: ” . As default text in the “ Text to extract: ” TextView, I set the text to the Declaration of Independence. I have included a text fi le containing the declaration, or you could use your own text or just provide text at runtime. Delete the default text from the extracted terms TextView. Next, you need to hook up the TextViews to the proper outlets in Interface Builder. Hook up the Extract Terms button to the IBAction extractTerms in File ’ s Owner. In the TermExtractViewController.m implementation fi le, implement a stub extractTerms method to log when someone calls the method. You will use this to verify that you have correctly wired up the button in Interface Builder. Here is the stub code: - (IBAction) extractTerms:(id)sender { NSLog (@”extractTerms”); } Build and run the application. Click the extractTerms button and verify that you see the log message in the console. This shows that you have correctly wired the button to the method. If you do not see the message in the console, make sure that you have properly wired the button to the message in Interface Builder. FIGURE 11 - 6: Term extract user interface CH011.indd 334CH011.indd 334 9/18/10 10:05:13 AM9/18/10 10:05:13 AM You are fi nished with the user interface, so you can close Interface Builder. Implementing the POST Call You will implement the extractTerms method to POST the request to the web service. The fi rst thing that you do in this method is to dismiss the keyboard by calling the resignFirstResponder method on the TextView. Next, you clear the list of extracted terms to eliminate old results: - (IBAction) extractTerms:(id)sender { NSLog (@”extractTerms”); // Hide the keyboard [self.textToExtractTextView resignFirstResponder]; // Clear the old extracted terms self.extractedTermsTextView.text = @””; TermExtractViewController.m Now, you create a string to hold the URL that you plan to call. This is the address of the Yahoo! Term Extraction web service. Next, you create an NSURL object with this string: // Create a string for the URL NSString *urlString = @”http://search.yahooapis.com/ContentAnalysisService/V1/termExtraction”; // Create the NSURL NSURL *url = [NSURL URLWithString:urlString]; TermExtractViewController.m The next line is where using the POST method differs from using GET . If you recall, when using the GET method, you simply set the URL string, set the parameter values inline, and sent the request off through the NSURLConnection . When using the POST method, you need to do things a little differently. After you create the NSURLRequest , you will need to modify some of its properties. Therefore, you must use an NSMutableURLRequest instead: // Create a mutable request because we will append data to it. NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval: 30.0]; TermExtractViewController.m Example 2: Term Extraction ❘ 335 CH011.indd 335CH011.indd 335 9/18/10 10:05:14 AM9/18/10 10:05:14 AM 336 ❘ CHAPTER 11 INTEGRATING WITH WEB SERVICES The fi rst change that you will make to the request is to set the HTTP method that you plan to use. Remember that you are using the POST method. The default method is GET , so you have to change this in the request to POST using the setHTTPMethod method: // Set the HTTP method of the request to POST [request setHTTPMethod:@”POST”]; TermExtractViewController.m Next, you will build a string to hold your parameters. In this example, there is only one parameter, but many parameters can optionally be passed using the POST method. You should note that parameters must be passed using the HTML parameter passing syntax name=value just like when using the GET method. In your implementation, make sure that you replace the appid with the actual appid that you receive from Yahoo! after you register your application. Here is your parameter string: // Build a string for the parameters NSString *parameters = [[NSString alloc] initWithFormat: @”appid=YOUR_ID_GOES_HERE & context=%@”, self.textToExtractTextView.text]; TermExtractViewController.m When you use the GET method to call a web service, you pass the parameters in the query string of the HTTP request. However, when you use POST , you pass those parameters in the body of the HTTP message. Therefore, you have to set the HTTP body using the setHTTPBody method: // Set the body of the request [request setHTTPBody:[parameters dataUsingEncoding:NSUTF8StringEncoding]]; TermExtractViewController.m The rest of the code for the method is the same as you have seen before. First, you create the NSURLConnection : NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self]; TermExtractViewController.m Next, you instantiate your responseData property: // Make sure that the connection is good if (connection) { // Instantiate the responseData data structure to store to response self.responseData = [NSMutableData data]; } CH011.indd 336CH011.indd 336 9/18/10 10:05:15 AM9/18/10 10:05:15 AM else { NSLog (@”The connection failed”); } TermExtractViewController.m Finally, you need to clean up your local variables: // Clean up our local variables [urlString release]; [parameters release]; TermExtractViewController.m Here is the complete method implementation: - (IBAction) extractTerms:(id)sender { NSLog (@”extractTerms”); // Hide the keyboard [self.textToExtractTextView resignFirstResponder]; // Clear the old extracted terms self.extractedTermsTextView.text = @””; // Create a string for the URL NSString *urlString = @”http://search.yahooapis.com/ContentAnalysisService/V1/termExtraction”; // Create the NSURL NSURL *url = [NSURL URLWithString:urlString]; // Create a mutable request because we will append data to it. NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval: 30.0]; // Set the HTTP method of the request to POST [request setHTTPMethod:@”POST”]; // Build a string for the parameters NSString *parameters = [[NSString alloc] initWithFormat: @”appid=YOUR_ID_GOES_HERE & context=%@”, self.textToExtractTextView.text]; // Set the body of the request [request setHTTPBody:[parameters dataUsingEncoding:NSUTF8StringEncoding]]; // Create the connection and send the request Example 2: Term Extraction ❘ 337 CH011.indd 337CH011.indd 337 9/18/10 10:05:16 AM9/18/10 10:05:16 AM 338 ❘ CHAPTER 11 INTEGRATING WITH WEB SERVICES NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self]; // Make sure that the connection is good if (connection) { // Instantiate the responseData data structure to store to response self.responseData = [NSMutableData data]; } else { NSLog (@”The connection failed”); } // Clean up our local variables [urlString release]; [parameters release]; } TermExtractViewController.m Receiving the XML Response In order to receive the response from the web service, you need to implement the NSURLConnection delegate methods as you did in the previous example. First, you will implement the connection:didReceiveResponse: method. This delegate method is called when the NSURLConnection creates the response. The connection could call this method multiple times, so you need to reset your response data by setting its length to zero each time this method runs. Here is the implementation: // Called when the connection has enough data to create an NSURLResponse - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { NSLog (@”connection:didReceiveResponse:”); NSLog(@”expectedContentLength: %qi”, [response expectedContentLength] ); NSLog(@”textEncodingName: %@”, [response textEncodingName]); [self.responseData setLength:0]; } TermExtractViewController.m Next, you need to implement the connection:didReceiveData: delegate method. The connection calls this method each time it receives data so you need to append the received data to your responseData buffer: // Called each time the connection receives a chunk of data - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { CH011.indd 338CH011.indd 338 9/18/10 10:05:16 AM9/18/10 10:05:16 AM . dataUsingEncoding:NSUTF8StringEncoding]]; // Create the connection and send the request Example 2: Term Extraction ❘ 337 CH011.indd 337CH011.indd 337 9/18/10 10:05:16 AM9/18/10 10:05:16 AM 338 ❘ CHAPTER 11 INTEGRATING WITH WEB. method called parseXML that you will invoke to start the XML processing: - (IBAction) extractTerms:(id)sender; - (void) parseXML; The complete header should look like this: #import <. *extractedTermsTextView; @property (nonatomic, retain) NSMutableData *responseData; - (IBAction) extractTerms:(id)sender; - (void) parseXML; @end TermExtractViewController.h In the implementation