Daniel Dickison
A collection of wrappers around various UIKit classes to give them blocks-based APIs.
The advantage of using blocks is that you can keep your event-handling logic closer to other related bits of code. For example, the DDBlockAlert class lets you add buttons along with the handler block, instead of having to create a separate method in a delegate that branches based on the clicked button index. It saves even more branching when a single delegate must be able to handle multiple different alerts.
DDBlockTableDelegate is a UITableViewDelegate and UITableViewDataSource that lets you specify cell specs from which the various table cell behaviors are derived. This is in contrast to the "normal" way of having your data source method branch depending on the cell indexPath that is passed in. The blocks-based API is particularly suited for tables which have few but greatly varying cells, for example in a settings-type UI where each cell holds a different type of interactive UI element. It is less suited for long, homogeneous lists as it creates a cell spec object for each row, which may be inefficient. (However you can reuse the handler blocks, so it might not be so bad.)
// An ivar:
UIAlertView *fooBarAlert;
// Elsewhere, to bring up the alert.
fooBarAlert = [[UIAlertView alloc] initWithTitle:@"Title" message:@"Message" cancelButtonTitle:@"Cancel" otherButtonTitles:@"Foo", @"Bar", nil];
fooBarAlert.delegate = self;
[alert show];
// Elsewhere
- (void)alertView:(UIAlertView *)alert clickedButtonAtIndex:(NSInteger)buttonIndex
{
if (alert == fooBarAlert)
{
if (buttonIndex == 1)
NSLog(@"Tapped foo.");
else if (buttonIndex == 2)
NSLog(@"Tapped bar.");
}
// else handle other alerts.
}
DDBlockAlert *alert = [DDBlockAlert alertWithTitle:@"Title" message:@"Message"];
[alert addCancelButtonWithTitle:@"Cancel" handler:^{}];
[alert addButtonWithTitle:@"Foo" handler:^{NSLog(@"Tapped foo.");}];
[alert addButtonWithTitle:@"Bar" handler:^{NSLog(@"Tapped bar.");}];
[alert show];
Drag the DDUIBlocks directory to your Xcode project, and include them in your target build. Then, in your source files, #import "DDUIBlocks.h".
See the demo project for example usage.
While the use of blocks simplifies many aspects of the API, it adds a major complication in terms of memory management. Blocks used as handlers are copied to the heap when added as event handlers to the DDUIBlocks classes. Furthermore, all blocks retain objects that are referenced in the block body. So if your block refers to self, or the UI object that owns the block, it will create a retain cycle resulting in a memory leak.
The workaround is to use the __block modifier for any local variables to which your blocks refer. You can assign self to another local variable (e.g. __block id blockSelf). A local variable marked with __block will not be retained by blocks. As long as you can ensure that the block will never be called after your own objects have been disposed, you can use the __block modifier safely. This condition should be generally true for use of DDUIBlocks classes because your parent object (e.g. the view controller) will "own" the DDUIBlocks object, which in turn "owns" the handler blocks.
For more info on blocks and retain cycles, see these links:
Copyright (c) 2011, Daniel Dickison All rights reserved.
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