Problems presenting view controller from clickedButtonWithIndex on iPad with iOS 8

As I work through my apps, I keep finding nifty iOS 8 issues. Such as one where I am having problems presenting a view controller from the clickedButtonWithIndex delegate method on an iPad with iOS 8.

From my research, it appears that under the covers, Apple is taking my UIActionSheet and morphing it into a UIActionController on the iPad in iOS 8. Unfortunately, weird things can happen if you try to present another view controller from within the clickedButtonWithIndex method, as the alert controller is still visible when the new controller is being presented. As a result, you get a warning message in the console that looks something like this:

Warning: Attempt to present <NewViewController: 0x12345678> on <OldViewController: 0x98765432> which is already presenting <UIAlertController: 0x24682468>

The solution to this seems to be to react to the didDismissWithButtonIndex method on UIAlertViewDelegate. When this is done, the alert controller appears to be gone on the iOS 8 iPad by the time that the new view controller is presented, and all is happy.

BTW, a posthumous Happy Birthday to Paul Butterfield, a fantastic artist who left us way too early. Luckily he is being immortalized in the Rock and Roll Hall of Fame, so more people should learn about him and experience his music.

CLGeocoder with built-in NSCache

In case you were wondering, Apple “recommends” that you only make one call per minute to their geocoding system. I can kind of understand the reasoning behind this, as they do not want to let people abuse the system. If you have a bunch of geocoding requests that you need to make within a short amount of time, you will not be cut off immediately if you push through a bunch of requests within seconds, but eventually you will get clipped. Now, if the requests you make are part of a table view that is scrolling, wouldn’t it be neat if you could find a CLGeocoder with built-in NSCache?

Well now you can. Please check out my GitHub repository for BPGeocoder:

https://github.com/Wave39/BPGeocoder

This class inherits from CLGeocoder and you use it as a replacement for CLGeocoder, except that it maintains its own NSCache of addresses that it has geocoded, and if you pass in an address it has already seen, it does not bother contacting the Apple servers, it just returns back the cached results it found earlier.

BTW, Happy Birthday to Terry Farrell, who played Valerie in Back To School and Lt. Dax on Star Trek: Deep Space 9, which was the best Star Trek series, IMHO. (Additionally, I think we need to get an internet campaign going to get IMDb to change the cast photo on their DS9 page to be one with Terry. Leave a comment if you agree. Sorry, Nicole!)

EXC_BAD_ACCESS when creating Address Book records on iOS

I have this code in one of my apps that creates some test records in the Contacts app, so that I can quickly build up some address book data for testing purposes. However, I just uncommented out this code for the first time in a long time, and now I am getting some kind of object release EXC_BAD_ACCESS exception when creating Address Book records on newer versions of iOS.

I tracked the problem down to this line:

ABMutableMultiValueRef phoneNumberMultiValue = ABMultiValueCreateMutable(kABPersonPhoneProperty);

While this used to work just fine, I needed to change it to this line:

ABMutableMultiValueRef phoneNumberMultiValue = ABMultiValueCreateMutable(kABMultiStringPropertyType);

And now my address book records are created without any kind of memory crash.

BTW, Happy Anniversary to Godzilla, who premiered in Japanese theaters on this day 60 years ago. Additional BTW, for U.S. readers, don’t forget to get out and vote tomorrow.

Monoprice mechanical keyboard

On a whim, I decided to take the plunge and pick up a Monoprice mechanical keyboard and see what all the fuss was about. Oh sure, I was alive during the clickety-clack days of the IBM PC-XT keyboard, which I am convinced was louder then using a Selectric typewriter.

The keyboard I purchased was a Monoprice MP-G9 mechanical gaming keyboard. This keyboard does not have backlighting, and has the Cherry MX Black switches. I must say I am impressed with the keyboard. It has that old timey feel without being deafeningly loud.

I could have spent a lot more money on a keyboard, but since I was not sure I was going to like this type of keyboard, I tried to spend as little as possible. I would have to say that my next keyboard purchase will be a more expensive model.

The only issue that I had with it was that I wanted to use it with my Mac, and the Windows and Alt keys are backwards from the configuration on my standard Apple keyboard. Luckily, the Keyboard section of System Preferences allows you to alter the modifier keys, so I went and assigned Option to the Command key and vice versa, and now all is happy.

BTW, Happy 45th Birthday to ARPANET, which first went online on this day in 1969.

Software update

(I have been waiting a while to post this picture, it seemed like a good idea to do it today what with the huge flap about the iOS 8.0.1 software update failure…)

I think my computer is trying to tell me that there is a software update…

update_dialog

BTW, Happy Birthday to Justin Bruening, who played Michael Knight on the Knight Rider TV series from 2008.

Cross a bridge at night

OK, here is a scenario. Four people on a journey together need to cross a bridge at night as quickly as possible. Among the four of them, they have one flashlight. They cannot continue their journey until all four reach the other side together. Since the bridge is narrow and slippery, and it is pitch black out being night and all, they decide to have two people cross with the flashlight, then one person returns with the flashlight back to the original side, and they continue until everyone is on the other side.

Oh, and also, the people can all walk at different paces, so when two people cross together, it takes them the amount of time that it takes the slower person to cover the distance.

For example, let’s say that the four people that need to cross can cover the distance of the bridge in 1 minute, 2 minutes, 5 minutes, and 10 minutes. What would be the shortest possible time?

The naive solution would be to have the 1 minute person be the primary flashlight runner and send them with the 2 minute person, return, then the 5 minute person, return, and finally cross with the 10 minute person, for a grand total of 19 minutes.

Now of course this is not the optimal solution, but more on that in a minute.

So how would we design an algorithm to solve this problem? Conventional wisdom says to create some kind of tree where you iterate through all of the possible combinations of initial crossings, then off those branches, combinations of reverse crossings, etc. Then once the tree is built, you can walk to all the branch tips and calculate the times, and then just display the shortest time.

But why do something logical? With all this computing power, I say that we implement my favorite algorithm for producing solutions to problems… The Monte Carlo method.

Here is the code for a C# .NET console app I threw together to solve this issue:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace BridgeAtNight
{
    public class BridgeState
    {
        public List<int> peopleOnLeft;
        public List<int> peopleOnRight;
        public int totalTime;
        public string peopleMovement;
 
        public BridgeState(int[] people)
        {
            totalTime = 0;
            peopleMovement = "";
            peopleOnLeft = new List<int>(people);
            peopleOnRight = new List<int>();
        }
 
        public void MoveLeftToRight(int leftToRight1, int leftToRight2)
        {
            peopleMovement = peopleMovement + string.Format("{0}>> {1}>> ", leftToRight1, leftToRight2);
            totalTime += Math.Max(leftToRight1, leftToRight2);
 
            peopleOnRight.Add(leftToRight1);
            peopleOnRight.Add(leftToRight2);
            peopleOnRight.Sort();
 
            peopleOnLeft.Remove(leftToRight1);
            peopleOnLeft.Remove(leftToRight2);
        }
 
        public void MoveRightToLeft(int rightToLeft)
        {
            peopleMovement = peopleMovement + string.Format("{0}<< ", rightToLeft);
            totalTime += rightToLeft;
 
            peopleOnLeft.Add(rightToLeft);
            peopleOnLeft.Sort();
 
            peopleOnRight.Remove(rightToLeft);
        }
 
        public void SolveWithNaivete()
        {
            peopleOnLeft.Sort();
            while (peopleOnLeft.Count > 1)
            {
                // move 2 people from the left to the right
                int leftToRight1 = peopleOnLeft[0];
                int leftToRight2 = peopleOnLeft[1];
                MoveLeftToRight(leftToRight1, leftToRight2);
 
                // move 1 person from right to left if there are any remaining people on the left
                if (peopleOnLeft.Count > 0)
                {
                    int rightToLeft = peopleOnRight[0];
                    MoveRightToLeft(rightToLeft);
                }
            }
 
            Console.WriteLine("Solution with naivete:");
            Console.WriteLine(string.Format("Time: {0} minutes", totalTime));
            Console.WriteLine(string.Format("Sequence: {0}", peopleMovement));
        }
 
        public void SolveRandomly()
        {
            Random rnd = new Random();
            while (peopleOnLeft.Count > 1)
            {
                // move 2 people from the left to the right
                var leftToRightRandom = peopleOnLeft.OrderBy(x => rnd.Next()).Take(2).ToList();
                int leftToRight1 = leftToRightRandom[0];
                int leftToRight2 = leftToRightRandom[1];
                MoveLeftToRight(leftToRight1, leftToRight2);
 
                // move 1 person from right to left if there are any remaining people on the left
                if (peopleOnLeft.Count > 0)
                {
                    var rightToLeftRandom = peopleOnRight.OrderBy(x => rnd.Next()).Take(1).ToList();
                    int rightToLeft = rightToLeftRandom[0];
                    MoveRightToLeft(rightToLeft);
                }
            }
        }
    }
 
    class Program
    {
        static void Main(string[] args)
        {
            BridgeState naiveBridgeState = new BridgeState(new int[] { 1, 2, 5, 10 });
            naiveBridgeState.SolveWithNaivete();
 
            List<string> bestTimeResults = new List<string>();
            int bestTime = 999999;
            for (int idx = 1; idx < 1000000; idx++)
            {
                BridgeState randomBridgeState = new BridgeState(new int[] { 1, 2, 5, 10 });
                randomBridgeState.SolveRandomly();
                if (randomBridgeState.totalTime < bestTime)
                {
                    Console.WriteLine(string.Format("Better random solution found in pass {0}:", idx));
                    Console.WriteLine(string.Format("Time: {0} minutes", randomBridgeState.totalTime));
                    Console.WriteLine(string.Format("Sequence: {0}", randomBridgeState.peopleMovement));
                    bestTime = randomBridgeState.totalTime;
                    bestTimeResults = new List<string>();
                    bestTimeResults.Add(randomBridgeState.peopleMovement);
                }
                else if (randomBridgeState.totalTime == bestTime)
                {
                    if (!bestTimeResults.Contains(randomBridgeState.peopleMovement))
                    {
                        Console.WriteLine(string.Format("Sequence: {0}", randomBridgeState.peopleMovement));
                        bestTimeResults.Add(randomBridgeState.peopleMovement);
                    }
                }
            }
 
            Console.WriteLine("Press any key to exit the application");
            Console.ReadKey();
        }
    }
}

There are undoubtedly some optimizations I can make to this code above, such as ordering the times in the MoveLeftToRight function. However, I was kind of surprised to see this run, as sometimes the optimal solution of 17 minutes was found in the first few thousand random walk throughs, and other times it would take a few hundred thousand walk throughs before the 17 minute solution was found. To me, it did not seem like there were enough different combinations that would make it so difficult to randomly find the solution.

For those who cannot/will not run this code, the crux of the biscuit, given the times of the walkers above (1 minute, 2 minutes, 5 minutes, and 10 minutes), is to send the slowest people across together once there is someone faster on the other side. Or in other words, first send 1 and 2 across, then have 1 come back. Then, send 5 and 10 across, and have 2 come back. Then 1 and 2 make the final crossing.

BTW, Happy Talk Like A Pirate Day today.

VB.NET simpler Async Await example

Well, I couldn’t let this rest, so here is an even simpler example of doing Async Await in VB.NET.

For this example code, I created a simple forms application with two buttons named cmdSynchronous and cmdAsynchronous, a label called lblStatus, and just to demonstrate the UI locking up effect, a combo box with some entries in it. Here is the code behind this form:

Public Class Form1
 
    Sub LongOperation()
 
        Threading.Thread.Sleep(5000)
 
    End Sub
 
    Private Sub cmdSynchronous_Click(sender As Object, e As EventArgs) Handles cmdSynchronous.Click
 
        lblStatus.Text = "Running a long operation synchronously... (UI thread should lock up)"
        Application.DoEvents()  ' needed here so that the label will update

        LongOperation()
 
        lblStatus.Text = "Done running the long operation synchronously."
 
    End Sub
 
    Private Async Sub cmdAsynchronous_Click(sender As Object, e As EventArgs) Handles cmdAsynchronous.Click
 
        lblStatus.Text = "Running a long operation asynchronously... (UI thread should be fully responsive)"
 
        Await Task.Run(Sub()
                           LongOperation()
                       End Sub)
 
        lblStatus.Text = "Done running the long operation asynchronously."
 
    End Sub
 
End Class

Notice that both button click events call the LongOperation method, which just sleeps for 5 seconds. However, the synchronous button click will lock up the UI (try to open the combo box, you will see that it waits until the sleep is done before displaying the choice list), whereas the asynchronous one will not.

Now in general, you would probably want to keep the tasks from piling up, as they would if you keep clicking the asynchronous button. I leave this as an exercise to the reader on preventing this problem.

BTW, Happy Birthday to Gary Hoey and Terje Rypdal, two of my favorite guitarists.

VB.NET simple Async Await example

I scoured the interwebs looking for a VB.NET simple Async Await example, and kind of came up empty. So, I decided to try to use bits and pieces of the examples I could find to roll my own.

The background here is that I am working on an application that accesses resources on the internet, and did not want to block the UI while the communications code was running.

Here is the code that I came up with:

Async Function GetDetails(theID As String) As Task
 
    Dim url As String
    url = GET_DETAILS_URL & "?theid=" & theID
 
    Dim request As WebRequest = WebRequest.Create(url)
    Dim response As WebResponse = Await request.GetResponseAsync()
    Dim dataStream As Stream = response.GetResponseStream()
    Dim reader As New StreamReader(dataStream)
    Dim responseFromServer As String = reader.ReadToEnd()
 
    reader.Close()
    response.Close()
 
    ' do something here with responseFromServer

End Function
 
Async Sub lstItems_SelectedIndexChanged(sender As Object, e As EventArgs) Handles lstItems.SelectedIndexChanged
 
    Dim idx As Integer = lstItems.SelectedIndex
 
    ' get the selected item
    Dim theItem As Object = itemsList(idx)
    Dim theItemID As String = theItem.itemID.ToString()
    Await GetDetails(theItemID)
 
End Sub

BTW, Happy Bennington Battle Day to our Green Mountain friends.

Twitter REST API is very finicky

The post title says it all.

I have been trying to put together some code that calls the Twitter REST API, and found it to be extremely finicky. If you do not have everything just right, you will get back a frustrating error message that says “Could not authenticate you” and “code 32″. Not super helpful.

Most of the issues I had were in building the base string that gets sent to Twitter. If this string is not built exactly as it needs to be built, things will just not work.

Here is what I found about building the base string through trial and error, and with exhaustive searches of the Google and Stack Overflow:

  • After the endpoint URL, make sure that your query string parameters are in alphabetical order
  • If you are putting into the base string part of a query that needs to be URL encoded, then it needs to be double encoded inside the base string

For example, on this double encoding thing, if you want to search for “Twitter API”, the search part of your query string, once URL encoded would look like this:

%26q%3DTwitter%20API

However, you need to double encode the search text so that it looks like this instead:

%26q%3DTwitter%2520API

BTW, Happy Birthday to Brian May, guitarist from the legendary rock group Queen.

Swift (or in other words, “Et tu, Objective-C?”)

Well the WWDC keynote has come and gone. And what do you know, a developer conference keynote geared towards developers. I guess all those bloggers and press types that took up some of the WWDC tickets from us actual developers are pretty disappointed today, as there were no shiny new devices shown.

The big announcement in my opinion was Swift, which will be the successor to Objective-C for developing on the Mac and iOS platforms. It looks somewhat interesting, as yet again they have lowered the bar and made it much easier to develop software for their platforms. But this is a disadvantage as well as a strength, as folks will continue to churn out the clones and inferior products that clutter up the App Store.

I applaud Apple for creating Swift and not recycling an existing language such as Ruby, Python, or Javascript, as these languages all come with their own baggage. Hopefully I will not be throwing away the 6 years of experience that I have built up with Objective-C and they will allow it to be used for the foreseeable future.

Ah, I miss the days when retain/release separated the men from the boys in the iOS world…

There was some good news in the presentations from yesterday. In the Platforms State of the Union presentation, they indicated that the 100 device barrier for beta testing and internal testing will essentially be rendered moot through Apple’s integration of TestFlight. This feature can’t come soon enough for me, so please hurry up Apple.

BTW, so many birthdays today, not sure where to begin… Kerry King of Slayer (happy 50th), Ian Hunter most famously of Mott the Hoople, Chuck Barris of the Gong Show… But the name that jumps out for me is Tristan Rogers, currently portraying Colin on The Young And The Restless. Happy Birthday, mate!