Open Source

ESSSquareProgressIndicator animating

What Is ESSSquareProgressIndicator?

It’s an indeterminate progress indicator originally developed for the iOS game ZEN.

It uses Core Animation (specifically, CAShapeLayers) to do its job and it’s pretty straight forward.

CGPathRefs, CAShapeLayer

CAShapeLayer has two animatable properties – -strokeStart and -strokeEnd (with a minimum value of 0.0 – start of path – and 1.0 – end of path). Going beyond 1.0 or below 0.0 doesn’t work.

So when trying to animate those values along a rectangular path – which was the first thing I tried when creating this – you do get a nice animation, but it ends at the 0.0/1.0 (which is, basically, the same) mark. So you end up with something like this:

glitchy progress indicator animation

The goal, then, was to animate beyond 1.0. The solution I came to – I’m sure there are other ways – was to use a second CAShapeLayer that animated alongside the first for the last/first part of the animation.

For a square, the values of the CAShapeLayer’s -strokeStart and -strokeEnd are as follows (starting at the top left corner):

CAShapeLayer strokeStart strokeEnd values

The CGPath begins and ends in the top left corner because I drew the path that way (you could make it start in the lower left corner or in the middle of a side, it all depends on where you start the CGPath with CGPathMoveToPoint).

The progress indicator starts at the middle of the left line and reaches to the middle of the top line. These are the two CAShapeLayers at work. The left part is one shape layer, the top line is another. I’ll do this in pictures I drew in code so it’s simpler to understand (the lines represent where the layer animated to, the dots are the invisible rest of the square).


Animation Part 1We start at this position. The line to the left is layer2(strokeStart:0.875, strokeEnd:1.0), the line at the top is layer1(strokeStart:0.0, strokeEnd:0.125).

Animation Part 2The transition to this is the reason we need two layers as we can not animate one layer beyond the 1.0 value.
So we animate layer2 to (1.0, 1.0) and at the same time animate layer1 to (0.0, 0.25) which makes it look like one line moving.

Animation Part 3This next part is easy. We animate layer1 to (0.75, 1.0).

Animation Part 4Lastly, we animate with two layers again to get to the initial position so we can repeat the whole thing from there on.
We animate layer2 from (0.75, 1.0) to (0.875, 1.0) and layer1 from (0.0, 0.0) to (0.0, 0.125) at the same time, again making it look like one line moving.

The Source Code

The repository (a sample iOS app, but the class works the same on OS X) is available on Github.

It was developed for iOS 7.1 but should work on earlier systems, and has been tested on OS X Yosemite, but should work on earlier systems as well.

You just drop in an ordinary UIView or NSView and set its class to ESSSquareProgressIndicator. Done. You can then set the color and stroke width right within Interface Builder thanks to the fairly new Xcode macros IB_Designable and IBInspectable.

Open Source

I have some more source code available here (or directly on my github profile page) if you’re interested. If you have any questions or feedback regarding this progress indicator, please be sure to mail or tweet me 😉


My name is Matt, I’m the developer of Eternal Storms Software. If you’d like to comment, you can catch me on twitter here: [twitter-follow screen_name=’eternalstorms’ show_count=’yes’] or by eMail.

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For the upcoming action extension in Transloader, I’m using a UIWebView to show the webpage the user is currently browsing, so they can tap on a link they’d like to download:

UIWebView without zoomTransloader’s Action Extension, displaying a UIWebView

It’s nice, but I wanted to go an extra step. A user might zoom and scroll in Safari before launching the action extension and when they do, the web page would be shown from the top, not zoomed. Here’s how I changed that.

Context and Flow

One of the main purposes of an action extension is to allow a user access to functionality from a different app without a) leaving the current app and b) without leaving the current context (which is more or less the same, but context is the point I’d like to drive home with this post).

In that vain, I thought it would be neat to present the website a user was viewing in Safari the same way in the action extension – meaning the zoom level and scroll position.

I figured, a user browses a site, perhaps zooms in on stuff and when they find a link they’d like to download to their Mac, they press the Share button in Safari and select Transloader’s action extension.

The thing is, the UIWebView of the extension loads the website for itself again and hence starts from the top, not zoomed in. So the user is ripped out of the context, they’d have to scroll and zoom again to get to the same position they had in the Safari web view. I wanted to change that:
A user should see the same part of the website in Transloader’s action extension as the part they were viewing in Safari before tapping the Share button.

Luckily, Apple implemented a way that allows us to do just that.

Java Script Preprocessing

In an Action extension for webpages (action extensions that are displayed in the action sheet if the NSExtensionActivationSupportsWebPageWithMaxCount criteria is met), you can supply a JavaScript preprocessing file that will let you examine the contents of the webpage before your native code is called.

This way, we can extract the current page scale and the scroll position. Here’s how we do that. In the Action.js, we call our native code with these parameters:


– pageXOffset is the horizontal scroll value
– pageYOffset is the vertical scroll value
– pageScale is how far the user has zoomed into the page
– baseURI is the current URL displayed in Safari

With these parameters, we can do what we set out to do – display the web page in the Action extension the same way as the user left it in Safari.

In our implementation file, in the WebView’s delegate method “-webViewDidFinishLoad:”, all we basically need to do is apply these parameters to our own web view:

[self.webView.scrollView setZoomScale:self._pageScale

[self.webView stringByEvaluatingJavaScriptFromString:[NSString stringWithFormat:@”window.scrollTo(%ld,%ld)”,self._pageXOffset,self._pageYOffset]];

For a complete project of how this exactly works, please scroll down where you’ll find a Xcode Project on Github.

And this is what it looks like in action – notice that after the Action extension is tapped, the website appears the same way as it was in Safari:

UIWebView Zoom and Scroll in Action

Example Project

TL;DR – I uploaded a demo project here on Github.

I hope you can make good use of this code – and if you do, please be sure to let me know! 🙂

My name is Matt, I’m the developer of Eternal Storms Software. If you’d like to comment, you can catch me on twitter here: [twitter-follow screen_name=’eternalstorms’ show_count=’yes’] or by eMail.

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Open-Source: NSBegin*AlertSheet(…) with ^Blocks

There’s NSBeginAlertSheet, NSBeginInformationalAlertSheet and NSBeginCriticalAlertSheet, so the * is a wild-card for all those functions.

Apple Opensource Icon

picture credit: Apple, Inc.

What is this?

I’ve been growing more and more tired of always having to set up a callback-method (in the worst case, two, for didDismiss and didEnd) for NSBegin*AlertSheet(…) calls, like

– (void)alertSheet:(NSPanel *)panel endedWithCode:(NSInteger)returnCode contextInfo:(void *)info
 …code here…

Especially, since we have such a great thing like blocks where you can pass blocks of code as arguments to methods and functions, just like an Objective-C object.

So instead of having to set up callback methods for NSBegin*AlertSheet(…), I created ESSBegin*AlertSheet(…). Instead of callback @selectors, it takes blocks for didEnd and didDismiss callbacks.

I find it also makes for cleaner code having the callbacks right in the ESSBegin*AlertSheet(…) calls as you don’t lose the context of what’s happening before the call in my code.

Available for OS X Snow Leopard and up

Blocks were introduced with OS X Snow Leopard, so I assume (yes, I assume since I’ve only tested this on OS X Mountain Lion) it should run on Snow Leopard as well.

Download and Usage

NSApplication+ESSApplicationCategory Github Repository (refer to the read me for how to implement it in your projects)
Eternal Storms Software Open Source Projects




Enjoy! And let me know what you think 🙂

Take care,

[twitter-follow screen_name=’eternalstorms’ show_count=’yes’]

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