Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>It sounds like what you're after is a mixin: define a series of methods that form the behaviour that you want, and then add that behaviour to only the set of classes that need it.</p> <p>Here is a strategy I've used to great success in my project <a href="https://github.com/sharplet/EnumeratorKit" rel="noreferrer">EnumeratorKit</a>, which adds Ruby-style block enumeration methods to built-in Cocoa collection classes (in particular <a href="https://github.com/sharplet/EnumeratorKit/blob/master/EnumeratorKit/Core/EKEnumerable.h" rel="noreferrer"><code>EKEnumerable.h</code></a> and <a href="https://github.com/sharplet/EnumeratorKit/blob/master/EnumeratorKit/Core/EKEnumerable.m" rel="noreferrer"><code>EKEnumerable.m</code></a>:</p> <ol> <li><p>Define a protocol that describes the behaviour you want. For method implementations you are going to provide, declare them as <code>@optional</code>.</p> <pre class="lang-c prettyprint-override"><code>@protocol WritableView &lt;NSObject&gt; - (void)writeText:(NSString *)text; @optional - (void)setTextToDomainOfUrl:(NSString *)text; - (void)setTextToIntegerValue:(NSInteger)value; - (void)setCapitalizedText:(NSString *)text; @end </code></pre></li> <li><p>Create a class that conforms to that protocol, and implements all the optional methods:</p> <pre class="lang-c prettyprint-override"><code>@interface WritableView : NSObject &lt;WritableView&gt; @end @implementation WritableView - (void)writeText:(NSString *)text { NSAssert(@"expected -writeText: to be implemented by %@", [self class]); } - (void)setTextToDomainOfUrl:(NSString *)text { // implementation will call [self writeText:text] } - (void)setTextToIntegerValue:(NSInteger)value { // implementation will call [self writeText:text] } - (void)setCapitalizedText:(NSString *)text { // implementation will call [self writeText:text] } @end </code></pre></li> <li><p>Create a category on <code>NSObject</code> that can add these methods to any other class at runtime (note that this code doesn't support class methods, only instance methods):</p> <pre class="lang-c prettyprint-override"><code>#import &lt;objc/runtime.h&gt; @interface NSObject (IncludeWritableView) + (void)includeWritableView; @end @implementation + (void)includeWritableView { unsigned int methodCount; Method *methods = class_copyMethodList([WritableView class], &amp;methodCount); for (int i = 0; i &lt; methodCount; i++) { SEL name = method_getName(methods[i]); IMP imp = method_getImplementation(methods[i]); const char *types = method_getTypeEncoding(methods[i]); class_addMethod([self class], name, imp, types); } free(methods); } @end </code></pre></li> </ol> <p>Now in the class where you want to include this behaviour (for example, <code>UILabel</code>):</p> <ol> <li>Adopt the <code>WritableView</code> protocol</li> <li>Implement the required <code>writeText:</code> instance method</li> <li><p>Add this to the top of your implementation:</p> <pre class="lang-c prettyprint-override"><code>@interface UILabel (WritableView) &lt;WritableView&gt; @end @implementation UILabel (WritableView) + (void)load { [self includeWritableView]; } // implementation specific to UILabel - (void)writeText:(NSString *)text { self.text = text; } @end </code></pre></li> </ol> <p>Hope this helps. I've found it a really effective way to implement cross-cutting concerns without having to copy &amp; paste code between multiple categories.</p>
    singulars
    1. This table or related slice is empty.
    1. POCreating a category for classes that implement a specific protocol in Objective-C?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USAdam Sharp
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POCreating a category for classes that implement a specific protocol in Objective-C?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COAwesome! Thanks for the detailed answer. I wish Apple made it as simple as `@interface UIView<WritableView> (foo)` though.
      singulars
      1. PO
      1. USSenseful
    2. CO@Senseful Yeah not to mention that in RubyMotion you could just `include WriteableView`. Still, it's great that the runtime allows it at all!
      singulars
      1. PO
      1. USAdam Sharp
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload