Load an XML file in Mac Os X using Cocoa: NSXMLDocument

Here another snippet on how to load an XML file using the NSXMLDocument class. Our goal is to show an “Open File” dialog box (as said in the last post), chose an xml file, and put it in a data structure (NSXMLDocument)

Here’s the code:

-(BOOL) LoadXml : (NSError **)err
{
    NSURL *fileUrl = nil;
    
    NSOpenPanel* openDlg = [NSOpenPanel openPanel];
    [openDlg setCanChooseFiles:YES];
    [openDlg setCanChooseDirectories:NO];
    [openDlg setAllowsMultipleSelection: NO];
    [openDlg setAllowedFileTypes:[NSArray arrayWithObjects:@"xml", 
             nil]];
    if ( [openDlg runModal] == NSOKButton )
    {
        fileUrl = [openDlg URL];
    }
    if (fileUrl==nil)
    {
        return NO;
    }
    
    xmlDoc = [[NSXMLDocument alloc] initWithContentsOfURL:fileUrl 
       options:(NSXMLNodePreserveWhitespace|NSXMLNodePreserveCDATA)
       error:err];
    if (xmlDoc == nil) {
        xmlDoc = [[NSXMLDocument alloc] initWithContentsOfURL:fileUrl
           options:NSXMLDocumentTidyXML error:&err];
    }
    if (xmlDoc == nil) 
  return NO;
    
    ...
}

The only “strange” thing suggested by the Apple’s example and reported here, is the double initialization of NSXMLDocument, with different parameters: the first one with NSXMLNodePreserveWhitespace|NSXMLNodePreserveCDATA, the second one with NSXMLDocumentTidyXML.

We are trying to recover from parsing errors. NSXMLDocumentTidyXML reformats the document before the parsing. Hopefully it can correct some error, but it modifies the original file (take a look at the documentation).

More information is in the “Introduction to Tree-Based XML Programming Guide for Cocoa” on the Apple Devveloper web site.

Open a file from the Mac OSX GUI: NSOpenPanel

This is a quick snippet that presents how to show a dialog to choose a file in Mac OS X programming in Objective-C. We will use the NSOpenPanel class.

Our first step is to write an IBAction routine, to answer to the user input, and link it to the interface (using XCode).

-(IBAction) action_OpenFile: (id) sender
{
}

Then we can populate it instantiating the NSOpenPanel class:

NSOpenPanel* openPanel = [NSOpenPanel openPanel];

This instantiate the class using the autorelease feature, so you don’t have to release it. Now you can personalize it using the features you need. For example the lines allow the user to choose just one file and not the directories:

[openPanel setCanChooseFiles:YES];
[openPanel setCanChooseDirectories:NO];
[openPanel setAllowsMultipleSelection: NO];

But what about the file types?
You may want to allocate an array of NSString with the list of allowed file types, and assign it to the panel. The following lines limit the users to choose the text files (txt or doc):

NSArray *tarr = [NSArray arrayWithObjects:@"txt", @"doc", nil];
[openPanel setAllowedFileTypes:tarr ];

Now you can show the panel, check if the user pressed the OK button, and retrieve the url of the selected file:

if ( [openPanel runModal] == NSOKButton ){
 fileUrl = [openPanel URL];
}

Other methods runModal* exist to show the panel, but most of them are declared deprecated in the last OSX versions.

Here the final code:

-(IBAction) action_OpenFile: (id) sender
{
 NSOpenPanel* openPanel = [NSOpenPanel openPanel];
 [openPanel setCanChooseFiles:YES];
 [openPanel setCanChooseDirectories:NO];
 [openPanel setAllowsMultipleSelection: NO];
 NSArray *tarr = [NSArray arrayWithObjects:@"txt", @"doc", nil];
 [openPanel setAllowedFileTypes:tarr ];
 if ( [openPanel runModal] == NSOKButton )
 {
    fileUrl = [openPanel URL];
    // ...
    // Use the file
    // ...   
 }
}

Emilio

iPhone screenshots for the App Store

Apple suggests formatting the screenshots for iPhone and iPad with a specific resolution, and, possibly, without the status bar. If you use XCode to take the screenshots you can find that they are not exactly that way, and they are stored in png format.

Updating the screenshots could be a boring task, so why don’t you write a script taking advantage of ImageMagick that automatically crop your images and convert them in jpg? In that way they will be ready to be posted on the App Store and on your web site.

We want to do the following steps:

1. Crop the images to a specific width and height
2. Convert them in jpg to reduce their weight
3. Prepare some thumbnail for our web site

ImageMagick has several tools, we will just use mogrify. Our first goal is to cut the status bar. If you took the screenshot from an iPhone with the Retina Display, the bar will be 40 pixels tall. On the iPad will be 20 pixels tall. For example here there is a screenshot taken from our Sudoku:

The operation we want to apply is the “crop”. The original image’s size is 640x960 pixels on portrait Retina Displays (768x1024 on iPads). We want to take the area starting at 40 pixels from the top, with the size of 640x920 pixels. The way mogrify do this, is using the –crop flag:

mogrify –crop 640x920+0+40 imagename.png

If we want contextually convert the image to the jpeg format we can add the ‘-format’ flag

mogrify -format jpg –crop 640x920+0+40 imagename.png

What about the thumbnails creation? You just need to add another flag, ‘-thumbnail’ with the maximum thumbnail’s width and height

mogrify -format jpg –crop 640x920+0+40 -thumbnail 120x120 imagename.png

For more information you can check the ImageMagick Web Site (www.imagemagick.org), or take a look at their books:

Here is the complete script. It assumes that you called the screenshots with the names: screenshot_iphone_n.png and screenshot_ipad_n.png (where n is the picture number, e.g., screenshot_iphone_1.png, screenshot_iphone_2.png, …), and it stores the thumbnails in a subdirectory.

#!/bin/sh

# Installation directory of ImageMagick (if not in PATH)

IMDIR='/ImageMagick-6.6.7/bin'

# Crop flag for iPhone with Retina Display

CROP='-crop 640x920+0+40'

# Crop flag for iPad

CROPIPAD='-crop 768x1004+0+20'

# Thumbnails directory

THUMBSDIR=thumbs

# Thumbnail flag

THUMB='-thumbnail 120x120'

# Adjust the screenshots

$IMDIR/mogrify -verbose -format jpg $CROP screenshot_iphone*.png

$IMDIR/mogrify -verbose -format jpg $CROPIPAD screenshot_ipad*.png

# Make the thumbnails

mkdir $THUMBSDIR

$IMDIR/mogrify -format jpg $CROP -path $THUMBSDIR $THUMB screenshot_iphone*.png

$IMDIR/mogrify -format jpg $CROPIPAD -path $THUMBSDIR $THUMB screenshot_ipad*.png