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Category Archive for ‘Q&A’ rss

Asking Users for a Review


Yves Gonzales asked:

“Would you know what the URL scheme is for writing a review in the AppStore, launched from within an app in iPhone, which opens AppStore? (I want to ask users to leave a review.)”

At first I answered that I did not think this was possible. But Yves, with the help of trusty Mr. Google discovered a better answer than mine. There is in fact a possibility to get the mobile App Store app to open on the review page for a specific app.

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Add one Week and Skip Weekend

dbarret asks:

“I need some help with this issue and I’m hoping you have the time to point me in the right direction, here goes:

  1. I want to display today’s date in a UILabel, then with a button event, the tricky part…
  2. display a date 7 days in the future UNLESS it’s the weekend, then it will display the following Monday.

So basically I want to display ONLY weekdays, no weekends… it that even possible?”

Of course it is possible. In this case it’s not even very difficult.

I assume that you know how to display a UILabel and set its text. So in this article I’ll show how to enhance what we previously learned about adding days to NSDates and add extra code to also skip weekend days.

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Ignoring Certificate Errors on NSUrlRequest

Fabian asks:

I’m trying to request data from a website via HTTPS that does not have valid certificate. How can I ignore the certificate error?

When the iPhone makes a HTTPS request it verifies that the certificate used to encrypt the data has a valid root certificate authority. Usually – for big sites – this is provided by Thawte or Verisign or any other recognized Root Certification Authority (CA). A bundle of the public certificates of such CAs is installed in the OS and enables the client to know which CAs are valid.

The problem arises however if you don’t have the funds to purchase such a certificate from a CA, those are expensive. Or sometimes you want to create a certificate for your own use or testing. This is called self-signed certificates. Those are also deemed invalid at first glance, unless you tell your browser to accept these certificates. Or it may be the case of Twitter who seem to have an expired certificate on one of their API servers.

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Detect Roaming

hhyyy9 asks:

It’s possible to detect when device goes on roaming or out of home network and turn on / turn off the data connection?

Well, yes and no. Yes to the part of the question about detecting. No to changing a system setting.

You have no direct access at all to roaming or home network information. Probably via a private framework but Apple does not approve of apps using those. Though you could infer the currently used data network from the IP address range you get from the currently active cellular connection. Each provider will have certain IP ranges and if you collect these ranges then you could build up a database to detect such network switching.

Also wheres the point? There already IS a setting that allows you to disable data roaming.

general network

The fact remains that you still cannot mess with the data system setting, but only work within your app.

But this would not be an worthy Dr. Touch post if I didn’t share some cool knowledge, this time how you can get all the current IP addresses of your device. Something like “IPCONFIG /ALL” on Windows or “IFCONFIG” on Unix.

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Alternating Tableview Cell Backgrounds

Wanner asks:

“How can I make my cells alternate colors across multiple sections if the sections don’t always have the same number of rows?”

A nice effect that you sometimes see in table views like the app store app is when you alternate the tableview cell backgrounds between light and dark shades of a color.

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"Are You a Cocoa Crack?" Quiz (1)

These questions will show if you are really the Cocoa Crack you like to believe to be. To see the answer highlight the answer text with your mouse. No peeking! Respond in the comments how many you got correct.

Quiz: Warm Up. Why can you not add an NSInteger to an NSArray? With which extra step can you do it?

Answer: NSInteger is only a different name for a signed integer. It is not a class even though the name might suggest it is. Only instances of classes can be added to NSArrays. The extra step mentioned is to first create an NSNumber object from the integer which you can add to an NSArray.

Quiz: I have an outlet defined and my code compiles without error or warning. But when I try to connect in in Interface Builder it does not show up. Why?

@interface CocoaQuizViewController : UIViewController
	UILabel IBOutlet *myLabel;
@property (nonatomic, retain) UILabel IBOutlet *myLabel;

Answer: The IBOutlet is at the wrong position. It needs to be before the type UILabel. IBOutlet itself is defined to be replaced with empty text for compiling, that’s why it does not cause a syntax error. But Interface Builder is looking for this keyword in header files to know what outlets there are.

Quiz: What does the following code do? Variable age is defined as NSInteger. Is the syntax correct or is there something missing? It compiles fine, but why does it crash?

myLabel.text = age?[NSString stringWithFormat:@"%@", age]:@"";

Answer: If the variable age is not equal to zero then the result of stringWithFormat will be assigned to the label text. If it is zero then an empty string will be assigned. The format argument is wrong, %@ gets the description of an instance. Since age is probably a number the format argument needs to be %d. It crashes because objC tries to access the memory at position “age” which the app does not own and therefore causes an exception.

Quiz: The following three methods all allow you to connect the outlet in Interface Builder. What is the technical difference between them and which is the method recommended by Apple?

Variant 1:

@interface CocoaQuizViewController : UIViewController
	IBOutlet UILabel *myLabel;

Variant 2:

@interface CocoaQuizViewController : UIViewController
	IBOutlet UILabel *myLabel;
@property (nonatomic, retain) IBOutlet UILabel *myLabel;

Variant 3:

@interface CocoaQuizViewController : UIViewController
	UILabel *myLabel;
@property (nonatomic, retain) IBOutlet UILabel *myLabel;

Answer: Method 3 is the correct one that should be preferred according to Apple. The instance that gets loaded from the XIB gets retained, just in case which prevents accidental unloading in case of low memory. Method 2 has a superfluous IBOutlet next to the instance variable because in this case the compiler will use the property anyway. Method 1 also can be connected, but it does not retain the loaded instance. This might cause problems if the instance gets deallocated for some reason.

Quiz: Complete this code so that it becomes syntactically correct using no more than one additional word and two square brackets.

NSInteger myNumber = @"1000";

Answer: @”1000″ is in itself a NSString instance. Therefore you can use it as receiver for the method integerValue. NSInteger myNumber = [@"1000" integerValue];

Quiz: (Bonus Question) Why does the following code crash as soon as the property is set? What is the simple fix?


@interface MeasureLinealView : UIView
	NSUInteger minValue;
@property (nonatomic, assign) NSUInteger minValue;


#import "MeasureStripView.h"
@implementation MeasureStripView
@synthesize minValue;
#pragma mark Passthrough Properties
- (void) setMinValue:(NSUInteger)aVal
	// this overriding is absolutely necessary
	self.minValue = aVal;

Some other file

MeasureStripView *myMS;  // assume it is properly initialized and otherwise working
myMS.minValue = 100;   // this line crashes. If commented out the app works fine

Answer: Using self.minValue as an lvalue cases the setter method setMinValue to be called. This causes an endless loop running out of memory eventually. The fix is to remove the “self.” inside the setter because minValue is an instance variable and thus accessible just by it’s name throughout the class.

So how many did you catch? Be honest! If you also have a Cocoa riddle like these to contribute please mail them directly to me ( and I will publish them in this format.

How to Rename an Appthe

Andreas asks:

I need to rename my app to something else because the original name is a trademark of a UK-based company. After I replaced all instances of the name where I found it the name of the product is still the same. Now if I build the products stay red and I get “No launchable executable present at path.” I have changed the name EVERYWHERE. How can I fix that?

Apart from the quick fix that I found googling I am going to see if I can fix this in XCode myself. I’ll show all the steps for guidance and the “pro fix” at the end.

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Display Local HTML file in UIWebView

Stefan87 asks:

Is it possible to display a HTML File which was created by the application in a UIWebview?

I would like to provide a helpfile in HTML-Format in the webview.

I’ve read the documentation, but it seems that every loadprocess requires a URL ?

I wanted to do the very same thing for displaying the instructions in LuckyWheel. After some experimentation I found the following way to be the simplest for me.

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Wait a Week

Moshe asks:

“How can make my app show a message 1 week after an event? I want to show an alert view the first time the app is launched after at least 1 week has expired and the event is still true.”

This technique can be used for any kind of action you don’t want to do right away or somehow should be based on a value determined in a previous run of your app.
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Sending E-Mail Attachments

Ravikumar Gajjavelly asks:

I want to send email It contains image as an attachment.How can we send am to attach image.can anybody please give solution.

When creating my app GeoCorder I was faced with the exact same dilemma of needing to attach a file to an email. I did some research and this is what I found.

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