iOS: Save an Image in Camera Roll

Saving an image to the camera roll on the iPhone is as close as a method call in the UIKit. However, it takes a few steps to wrap together code to manage error handling and notification that the image has been saved. Let’s see how this works.

Let’s begin with the method description to save an image:

  void UIImageWriteToSavedPhotosAlbum(UIImage *image, 
                  id completionTarget, SEL completionSelector, void *contextInfo);

completionTarget refers to the object in which the completionSelector can be found. In other words, what object has the method that will be called once the file write is complete?contextInfo is a void * that you can use to specify content to be passed to thecompletionSelector.

Obviously, the image is a required paramater. The other three are only needed if you prefer to be notified asynchronously when the write is complete. Here’s how a call to the above method might look:

  // Image to save
  UIImage *img = [UIImage imageNamed:@"ImageName.png"];  

  // Request to save the image to camera roll
  UIImageWriteToSavedPhotosAlbum(img, self, 
              @selector(image:didFinishSavingWithError:contextInfo:), nil);

Here we are specifying that the selector to be called upon completion is within this object (self). A template for this selector could look as follows:

  - (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error 
             contextInfo:(void *)contextInfo
    // Was there an error?
    if (error != NULL)
      // Show error message...

    else  // No errors
      // Show message image successfully saved

Add code for displaying the appropriate message based on success or failure of the image save, and you’re good to go.


Python Tips: Function Chaining

Function chaining—lets you chain function calls together on a single line so the output of one becomes the input to another. Function chains are read right to left.



Python Tips: Method Chaining

Method chaining
—lets you chain method calls together on a single line so the output of one becomes the input to another. Method chains are read left to right.

myText = data().strip().split(',')

In this example, strip removes the unwanted leading and trailing white space in the text referenced by the variable data, and then the split extracts the strings separted by commas. A list is created and assigned to MyText. Notice that methods are executed from left to right.


GPG Cheat Sheet

Filenames are italicized (loosely, some aren’t, sorry), so if you see something italicized, think “put my filename there.”

I’ve used User Name as being the name associated with the key. Sorry that isn’t very imaginative. I *think* gpg is pretty wide in it’s user assignments, ie. the name for my private key is Charles Lockhart, but I can reference that by just putting in Lockhart. That doesn’t make any sense, sorry.

to create a key:
gpg –gen-key
generally you can select the defaults.

to export a public key into file public.key:
gpg –export -a “User Name” > public.key

This will create a file called public.key with the ascii representation of the public key for User Name. This is a variation on:
gpg –export
which by itself is basically going to print out a bunch of crap to your screen. I recommend against doing this.
gpg –export -a “User Name”
prints out the public key for User Name to the command line, which is only semi-useful

to export a private key:
gpg –export-secret-key -a “User Name” > private.key

This will create a file called private.key with the ascii representation of the private key for User Name.
It’s pretty much like exporting a public key, but you have to override some default protections. There’s a note (*) at the bottom explaining why you may want to do this.

to import a public key:
gpg –import public.key

This adds the public key in the file “public.key” to your public key ring.

to import a private key:
gpg –allow-secret-key-import –import private.key

This adds the private key in the file “private.key” to your private key ring. There’s a note (*) at the bottom explaining why you may want to do this.

to delete a public key (from your public key ring):
gpg –delete-key “User Name”
This removes the public key from your public key ring.
NOTE! If there is a private key on your private key ring associated with this public key, you will get an error! You must delete your private key for this key pair from your private key ring first.

to delete an private key (a key on your private key ring):
gpg –delete-secret-key “User Name”
This deletes the secret key from your secret key ring.

To list the keys in your public key ring:
gpg –list-keys

To list the keys in your secret key ring:
gpg –list-secret-keys

To generate a short list of numbers that you can use via an alternative method to verify a public key, use:
gpg –fingerprint > fingerprint
This creates the file fingerprint with your fingerprint info.

To encrypt data, use:
gpg -e -u “Sender User Name” -r “Receiver User Name” somefile

There are some useful options here, such as -u to specify the secret key to be used, and -r to specify the public key of the recipient.
As an example: gpg -e -u “Charles Lockhart” -r “A Friend” mydata.tar
This should create a file called “mydata.tar.gpg” that contains the encrypted data. I think you specify the senders username so that the recipient can verify that the contents are from that person (using the fingerprint?).
NOTE!: mydata.tar is not removed, you end up with two files, so if you want to have only the encrypted file in existance, you probably have to delete mydata.tar yourself.
An interesting side note, I encrypted the preemptive kernel patch, a file of 55,247 bytes, and ended up with an encrypted file of 15,276 bytes.

To decrypt data, use:
gpg -d mydata.tar.gpg
If you have multiple secret keys, it’ll choose the correct one, or output an error if the correct one doesn’t exist. You’ll be prompted to enter your passphrase. Afterwards there will exist the file “mydata.tar”, and the encrypted “original,” mydata.tar.gpg.

NOTE: when I originally wrote this cheat sheet, that’s how it worked on my system, however it looks now like “gpg -d mydata.tar.gpg” dumps the file contents to standard output. The working alternative (worked on my system, anyway) would be to use “gpg -o outputfile -d encryptedfile.gpg”, or using mydata.tar.gpg as an example, I’d run “gpg -o mydata.tar -d mydata.tar.gpg”. Alternatively you could run something like “gpg -d mydata.tar.gpg > mydata.tar” and just push the output into a file. Seemed to work either way.

Ok, so what if you’re a paranoid bastard and want to encrypt some of your own files, so nobody can break into your computer and get them? Simply encrypt them using yourself as the recipient.

I haven’t used the commands:
gpg –edit-key
gpg –gen-revoke

Sharing Secret Keys

NOTE!: the following use cases indicate why the secret-key import/export commands exist, or at least a couple ideas of what you could do with them. HOWEVER, there’s some logistics required for sharing that secret-key. How do you get it from one computer to another? I guess encrypting it and sending it by email would probably be ok, but I wouldn’t send it unencrypted with email, that’d be DANGEROUS.

Use Case *.1 : Mentioned above were the commands for exporting and importing secret keys, and I want to explain one reason of why maybe you’d want to do this. Basically if you want one key-pair for all of your computers (assuming you have multiple computers), then this allows you export that key-pair from the original computer and import it to your other computers.

Use Case *.2 : Mentioned above were the commands for exporting and importing secret keys, and I want to explain one reason of why maybe you’d want to do this. Basically, if you belonged to a group, and wanted to create a single key-pair for that group, one person would create the key-pair, then export the public and private keys, give them to the other members of the group, and they would all import that key-pair. Then a member of the group or someone outside could use the group public key, encrypt the message and/or data, and send it to members of the group, and all of them would be able to access the message and/or data. Basically you could create a simplified system where only one public key was needed to send encrypted stuffs to muliple recipients.

Oracle Client not able to connect to Oracle in other than Administrator user

Permissions on the folders (give users read and execute) and the “create global objects” security setting are the problem. Instructions to fix:

To resolve this issue, identify the users group that is used to run the program, and then assign the “Create global objects” user right to that users group. To do this, follow these steps:

1. Click Start, point to Programs, point to Administrative Tools, and then click Local Security Policy.
2. Expand Local Policies, and then click User Rights Assignment.
3. In the right pane, double-click Create global objects.
4. In the Local Security Policy Setting dialog box, click Add.
5. In the Select Users or Group dialog box, click local users group or the user account that you want to add, click Add, and then click OK.
6. Click OK.

Other reference points:

[b]Microsoft Knowledgebase Article[/b]: 821546

[b]Oracle Metalink Article[/b]: Doc ID: Note:342226.1 Subject: Starting SQL*Plus with Non-Administrator Account Fails with SP2-1503 SP2-0152

Python: Making a http post without form

There are times when it is required to post to url without the for data.
Port with Form

import urllib, mechanize

br = mechanize.Browser()

# log in"")
br["username"] = "test"
br["password"] = "test"
r = br.submit()
assert "Welcome" in r.get_data()

Post to a url without form
# now post a request without a form
data = urllib.urlencode({'some_var':'blah','another_var':'foo'})
r ="", data)

# print the response

Using CSS to overlay text on an image

Indeed there is a simpler, more flexible solution. Instead of a TABLE we use a DIV and CSS positional attributes to place futher text and images with relation to that DIV.

<div style="position: relative; background: url(path to image); width: (width)px; height: (height)px;"> <div style="position: absolute; bottom: 0; left: 0.5em; width: 400px; font-weight: bold; color: #fff;"> <p>(text to appear at the bottom left of the image)</p> </div> <p style="position: absolute; top: 1em; right: 2em; width: 120px; padding: 4px; background-color: #fff; font-weight: bold; font-size: 11px;"> (text to appear at the top right of the image) </p> </div>

As you can see, we are able to place any number of sub-elements within the surrounding div. In this case a div containing paragraphs with text (bottom left), and a paragraph by itself (top right).

The CSS approach is to use one DIV to define the area where the background image appears. This DIV has it’s position attribute set to relative in order that the items it contains can be properly placed.

This is done by setting the position attribute of contained items to absolute and placing them by setting one or more of the positional attributes:toprightbottom and left.

This block has been positioned at the top, right

The position attribute may seem complicated at first, but it’s the key to implementing complicated layouts without excessive amounts of code. Remember that you need to have a container element with it’s position attribute set to relative in order to layout subsequent content using absolute positioning.

Without a container element all positioning will be in relation to the viewport (the bottom of the screen). This in combination with position: fixed can create elements that stay in one corner of the screen and don’t move when the page scrolls, but only in browsers other than Explorer. On this site you might see a [top] link doing just that if you’re using a compatible browser.