我正在尝试在应用程序内为我的网站制作 RSS 提要。我正在努力做到这一点，以便当用户单击我的 TableView 中的一个单元格时，它会将您带到已解析的特定帖子的链接。正在解析链接，但控制台给了我这个错误：
应用程序试图在 target 上推送一个 nil 视图控制器。
这是我的代码：
WebViewController.h
#import <Foundation/Foundation.h>
@interface WebViewController : UIViewController
@property (nonatomic, readonly) UIWebView *webView;
@end
WebViewController.m
#import "WebViewController.h"
@implementation WebViewController
-(void)loadView
{
CGRect screenFrame = [[UIScreen mainScreen] applicationFrame];
UIWebView *wv = [[UIWebView alloc] initWithFrame:screenFrame];
[wv setScalesPageToFit:YES];
[self setView:wv];
}
-(UIWebView *)webView
{
return (UIWebView *)[self view];
}
@end
MasterViewController.h我的 TableView
#import <UIKit/UIKit.h>
// A forward declaration; we'll import the header in the .m
@class RSSChannel;
@class WebViewController;
@interface MasterViewController : UITableViewController
<NSXMLParserDelegate>
{
NSURLConnection *connection;
NSMutableData *xmlData;
RSSChannel *channel;
}
@property (strong, nonatomic) IBOutlet UITableView *tableView;
@property (strong, nonatomic) IBOutlet UINavigationItem *navigationBar;
@property (nonatomic, strong) WebViewController *webViewController;
- (void)fetchEntries;
@end
主视图控制器.m
#import "MasterViewController.h"
#import "WebViewController.h"
#import "RSSChannel.h"
#import "RSSItem.h"
@interface MasterViewController () {
NSMutableArray *_objects;
}
@end
@implementation MasterViewController
@synthesize tableView = _tableView;
@synthesize navigationBar;
@synthesize webViewController;
- (void)awakeFromNib
{
[super awakeFromNib];
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
[self fetchEntries];
}
- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
}
#pragma mark - Table View
- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section {
UIImage *myImage = [UIImage imageNamed:@"SephardiJewsHeader.png"];
UIImageView *imageView = [[UIImageView alloc] initWithImage:myImage];
imageView.frame = CGRectMake(0,-1,320,93);
return imageView;
}
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section {
return 93;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
NSLog(@"The amount of items in the table: %u", [[channel items] count]);
return [[channel items] count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell *cell = [tableView
dequeueReusableCellWithIdentifier:@"UITableViewCell"];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle
reuseIdentifier:@"UITableViewCell"];
}
RSSItem *item = [[channel items] objectAtIndex:[indexPath row]];
[[cell textLabel] setText:[item title]];
[[cell detailTextLabel] setText:[item date]];
return cell;
}
- (void)fetchEntries
{
// Create a new data container for the stuff that comes back from the service
xmlData = [[NSMutableData alloc] init];
// Construct a URL that will ask the service for what you want -
// Note we can concatenate literal strings together on multiple lines in this way it
// results in a single NSString instance
NSURL *url = [NSURL URLWithString:
@"http://sephardijews.com/feed/"];
// Putting the URL we made into an NSURLRequest, so we can connect to the url data that we specifed
NSURLRequest *req = [NSURLRequest requestWithURL:url];
// Creating a connecting that will exchange this request for the data from the URL we specifed
connection = [[NSURLConnection alloc] initWithRequest:req
delegate:self
startImmediately:YES];
}
- (void)parser:(NSXMLParser *)parser
didStartElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qualifedName
attributes:(NSDictionary *)attributeDict
{
NSLog(@"%@ found a %@ element", self, elementName);
if ([elementName isEqual:@"channel"]) {
// If the parser saw a channel, create new instance, store in our ivar
channel = [[RSSChannel alloc] init];
// Give the channel object a pointer back to ourselves for later
[channel setParentParserDelegate:self];
// Set the parser's delegate to the channel object
[parser setDelegate:channel];
}
}
// This method will be called several times as the data arrives
- (void)connection:(NSURLConnection *)conn didReceiveData:(NSData *)data
{
// Add the incoming chunk of data to the container we are keeping
// The data always comes in the correct order
[xmlData appendData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)conn
{
// Create the parser object with the data received from the web service
NSXMLParser *parser = [[NSXMLParser alloc] initWithData:xmlData];
// Give it a delegate - don't worry about the warning
[parser setDelegate:self];
// Tell it to start parsing - the documet will be parsed and the delegate of NSXMLParser will get all of its delegate messages sent to it before this line finishes execution - it is blocking
[parser parse];
// Get rid of the XML data as we no longer need it
xmlData = nil;
// Get rid of the connection, no longer need it
connection = nil;
// Reload the table
[[self tableView] reloadData];
NSLog(@"%@\n %@\n %@\n", channel, [channel title], [channel infoString]);
}
- (void)connection:(NSURLConnection *)conn didFailWithError:(NSError *)error
{
// Release the connection object, we are done with it cause' there is no connection
// Setting the connection to nil will stop the connection because it is nothing/0
connection = nil;
// Release the xmlData object. We stopped to connection to put the data in the xmlData object, so we set it to nil also
xmlData = nil;
// Grab the description of the error object passed to us, so we can tell the user
NSString *errorString = [NSString stringWithFormat:@"Fetch failed: %@", [error localizedDescription]];
// Create and show an alert view to the user with the error string to tell them the error in the process of the connection
UIAlertView *av = [[UIAlertView alloc] initWithTitle:@"Error"
message:errorString
delegate:nil
cancelButtonTitle:@"OK"
otherButtonTitles:nil];
[av show];
}
/* - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
WebViewController *aWebViewController = [[WebViewController alloc] init];
self.webViewController = aWebViewController;
[self.navigationController pushViewController:self.webViewController animated:YES];
RSSItem *entry = [[channel items] objectAtIndex:[indexPath row]];
NSURL *url = [NSURL URLWithString:[entry link]];
NSURLRequest *req = [NSURLRequest requestWithURL:url];
[[webViewController webView] loadRequest:req];
[[webViewController navigationItem] setTitle:[entry title]];
} */
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:@"showPost"]) {
WebViewController *awebViewController = [segue destinationViewController];
self.webViewController = awebViewController;
NSIndexPath *selectedRow = [self.tableView indexPathForSelectedRow];
RSSItem *entry = [[channel items] objectAtIndex:[selectedRow row]];
NSURL *url = [NSURL URLWithString:[entry link]];
NSURLRequest *req = [NSURLRequest requestWithURL:url];
[[webViewController webView] loadRequest:req];
[[webViewController navigationItem] setTitle:[entry title]];
}
}
@end
谢谢你的帮助！