Mac / iPhone App Development » programming

Adding Reachability Code to your app

admin — Tue, 26 Jan 2010 19:37:41 +0000

Ok so iVersion 1.4 was declined due to not loading correctly when their is no network connectivity.

When the device is connected to a cellular network, iVersion does not load its contents. After the user enters the URL (http://svn.collab.net/repos/svn/trunk/) and taps “connect,” an error message is received.

Apparently the error message is not clear enough or something, anyway this is not a rant, this is what apple recommends.

Please take a look at the Reachability iPhone program sample which demonstrates the use of the System Configuration Reachability API to detect the absence of WiFi and Wireless Wide Area Network (WWAN) services. Your application can then take appropriate action at the first point where network services are required.

The sample code can be found on Apple developer site, however the two file we are interested in are:

Download the Reachability Code:
Reachability.h

Reachability.m

How to use:
Lets say you have a simple UILabel which you want to update with either “(Offline)” or “(Online)” depending on whether the network is reachable. Your view controller would be defined something like this:

@interface MyStatusView : UIViewController
{
	UILabel * statusLabel;
}
 
@property(nonatomic, assign) IBOutlet UILabel * statusLabel;
 
- (void)reachabilityChanged:(NSNotification *)note;
- (void)updateStatus;
 
@end

Then we add the following code to the view controller .m file:

-(void)viewWillAppear:(BOOL)animated
{
	self.reachability = [Reachability reachabilityWithHostName:@"google.com"];
	[reachability startNotifer];
 
	[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name:@"kNetworkReachabilityChangedNotification" object:nil];
 
	[self updateStatus];
}
 
-(void)viewWillDisappear:(BOOL)animated
{
	self.reachability = nil;
	[[NSNotificationCenter defaultCenter] removeObserver:self];
}
 
-(void)reachabilityChanged:(NSNotification*)notification
{
	[self updateStatus];
}
 
-(void)updateStatus
{
	NSLog(@"Reachability changed");
 
	if ([reachability currentReachabilityStatus] == NotReachable)
	{
		statusLabel.text = @"(Offline)";
	}
	else
	{
		statusLabel.text = @"(Online)";
	}
}

I think it’s fairly self explanatory. Basically when the view appears the reachability class is created and started using startNotifier. Then we hook in our reachabilityChanged: method into the notification centre, so it is automatically called when the network status changes. reachabilityChanged: calls updateStatus which simply changes our label depending on the connectivity.

UIKit Modal Prompt

admin — Tue, 26 Jan 2010 19:20:05 +0000

in order to not lock the ui iVersion runs it’s svn commands in a seperate threads. The promblem arises when one of thses threads needs to prompt for a value e.g. a username / password. Firstly UIKit does not provide a modal alert view and secondly UIKit should only be called from the mainThread.

First we create a new class which has a view which will be loaded from a nib, a thread condition to lock the calling thread and two NSString fields to store the result and the string of the button which was clicked.

@interface MessagePrompt : NSObject
{
 
UIView * view;
NSCondition * promptCondition;
NSString * clickedButton Text;
NSString * result;
{
@end

Our new prompt method can be called from the thread which needs to be locked, it will subsequently call UIKit on the main thread.

+(id)newPrompt:(MessagePrompt*)prompt
{
 
     if ([NSThread currentThread] == [NSThread mainThread])
    {
          printf("Should not be called by Main thread\n");
          return nil;
    }
 
     prompt.promptCondition = [[[NSCondition alloc] init] autorelease];
 
    [prompt performSelectorOnMainThread:@selector(prompt:) withObject:view waitUntilDone:NO];
    [prompt.promptCondition wait];
 
    return prompt;
}

This method is called by +(id)NewPrompt and displays a prompt in our window. It also adds targets to each UIButton to receive user actions.

-(void)prompt:(UIView*)inView
{
     NSArray * nib = [[NSBundle mainBundle] loadNibNamed:@"MyPromptView" owner:self options:nil];
     inView = [nib objectAtIndex:0];	
 
     NSArray * subviews = [self.view subviews];
     for (UIView * cview in subviews)
    {
          if ([cview isKindOfClass:[UIButton class]])
          {
               UIButton * button = (UIButton*)cview;
                [button addTarget:self action:@selector(clicked:) forControlEvents:UIControlEventTouchDown];
          }
    }
 
    [inView.superview addSubview:view];
}

This is called when a user clicks a button, it finds the value field and retreives and stores the value in self.message. The prompt condition is then signalled which causes the calling thread to continue running.

-(IBAction)clicked:(UIButton*)sender
{
     self.clickedButton = sender.currentTitle;
 
     UITextView * text = [iVersionAppDelegate findSubViewOfKind:self.view class:[UITextView class]];
     if (text)
    {
         self.message = text.text;
    }
 
    [self.view removeFromSuperview];
     self.view = nil;
 
    [promptCondition signal];
}
 
@end

Usage

/* Called when svn requires a log message */
svn_error_t *
iversion_svn_cl__get_log_message(const char **log_msg,
const char **tmp_file,
const apr_array_header_t *commit_items,
void *baton,
apr_pool_t *pool)
{
 
CommitLogMessagePrompt * prompt = [CommitLogMessagePrompt newPrompt];
 
    /* Clicked Continue */
     if ([prompt.clickedButton isEqualToString:@"Continue"])
    {
        *log_msg = [prompt.message UTF8String];
         return SVN_NO_ERROR;
    }
 
     return svn_error_create(SVN_ERR_CANCELLED, NULL, _("Delete Cancelled"));
}

iPhone File System Monitor

admin — Tue, 26 Jan 2010 19:04:39 +0000

I require simple for system monitoring for a new (undisclosed) iphone project. It doesn’t appear that there is any equivilant to ionotify for the iphone, so I whipped up this polling file system monitor which meets my basic requirements. If you find this code useful feel free to use / distribute etc.

#include "FileSystemMonitor.h"
 
//Setup the monitor
FileSystemMonitor * monitor = [[FileSystemMonitor alloc] init];
monitor.delegate = self;
[monitor monitorPath:@"/"];
 
//...In your delegate class
-(void)nodeWasCreatedAt:(NSString*)path
{
     printf("Created %s\n", [path UTF8String]);
}
 
-(void)nodeWasDeletedAt:(NSString*)path
{
    printf("Deleted %s\n", [path UTF8String]);
}
 
-(void)fileSizeDidchange:(NSString*)path bytes:(size_t)difference
{
     printf("file Added %ul bytes\n", difference);
}

Notes:

Can monitor for Deleted files, Created Files and File Size Changes
On an iPhone 3GS it is able to monitor the entire SVN 1.6 source tree and the iVersion source tree (total 11,050 File/Directories) in an execution time of 12s. Due to the low thread priority and the fact that the majority of execution time is IO it does not cause much/any slow down to the UI. However there is still room for improvement.

Download:

FileSystemMonitor.h

FileSystemMonitor.m

FileMonitorDelegateProtocol.h

Dynamic Arrays with C

admin — Tue, 26 Jan 2010 17:12:05 +0000

In the final push to add syntax highlighting to iVersion I have been working on optimising the parser.

In the inner parsing loop I have been using the standard NSMutableArray to keep track of various objects and tokens. Objective C message passing is of course an order of times slower than a C function call, even if purely for the fact that they can’t be inlined. A great article that explains more about the objective c runtime an be found on the cocoa samurai blog

So I decided to drop down to a dynamic array using plain C. However even though I’m sure dynamic arrays have been implement thousands of times I couldn’t seem to find any simple implementations.

//** Usage
//Create an array with capacity 2
CArray * array = CArrayInit(2);
 
//Add two buckets
CArrayAdd(array, "test");
CArrayAdd(array, "another test");
 
//Add another and it will resize accordingly
CArrayAdd(array, "yet another");
 
//Print All
for (int ii = 0; ii &lt; array-&gt;count; ++ii)
{
        const char * buffer = CArrayObjectAtIndex(array, ii);
        printf("Index: %d - %s\n", ii, buffer);
}

Download:

CArray.h

CArray.c

Notes:
The following test function usually reports about 5x faster than NSMutableArray which I think is a credit to how efficient the Objective C library and messaging system really is considering all the things your missing out on (exceptions, null pointers etc)

void CArrayTestRoutine()
{
 
    CArray * array = CArrayInit(0);
 
    NSTimeInterval start = [[NSDate date] timeIntervalSince1970];
    NSString * test;
 
    for (int ii = 0; ii &lt; 10000000; ++ii)
    {
        CArrayAdd(array, @"test");
        test = CArrayObjectAtIndex(array, CArrayCount(array)-1);
    }
 
     CArrayRemoveObjectAtIndex(array, 0);
 
     NSTimeInterval end = [[NSDate date] timeIntervalSince1970];
     printf("CArray 100,000,000 Elements took %fs\n", end-start);
 
     NSMutableArray * nsarray = [[NSMutableArray alloc] initWithCapacity:0];
     start = [[NSDate date] timeIntervalSince1970];
     NSString * string;
 
     for (int ii = 0; ii &lt; 10000000; ++ii)
    {
        [nsarray addObject:@"test"];
        string = [nsarray objectAtIndex:[nsarray count]-1];
    }
 
    [nsarray removeObjectAtIndex:0];
 
     end = [[NSDate date] timeIntervalSince1970];
    [nsarray release];
     printf("NSMutableArray 100,000,000 Elements took %fs\n", end-start);
 
     printf("%s\n", [string UTF8String]);
     printf("%s\n", [test UTF8String]);
     CArrayDestroy(array);
 
}

iVersion

admin — Tue, 26 Jan 2010 17:06:43 +0000

iVersion is a SVN client for the iphone 3G and ipod touch.

iVersion uses the open source subversion 1.6 client library, written in plain C, with an Objective C wrapper for simpler interfacing with the Objective C UI. Using an objective C Wrapper the client can easily be abstracted to work with other version control protocols. In the future git, mercurialand bazaar support maybe included.

Features

Multi-threaded non-locking ui
OpenSSL support for https:// and svn+ssh:// connections
svn commands: list, info, cat,
Browse Directories
View Commit Logs
View file Info
Bookmarks, History & Directory Cache through NSUserDefaults

** Commit Support
Subversion does not allow commiting of a single file without a working copy of the previous directory. A work around for this has been found and commit support should be available in a future version.