Setting UIActivityIndicatorView while view is prepared - iphone

Question

I have a UITabbBarController with a UITableView. Under certain circumstances the TabBarControllers dataset requires updating when a user arrives from another view,
e.g. the initial load when the TabBarController is called the first time, or when the settings are changed.
This dataset update takes about 2 seconds and I want to show an UIActivityIndicatorView.
Trouble is that when I enter from another view I don't know which view to attach it to, since the loading of the tabbarController is carried out in the viewWillAppear method.
Any clues how I can go about this?

Answer 1

I've done this sort of thing in the viewDidAppear method. My code kicks off a background task to load the data from a url. It also hands the background task a selector of a method to call on the controller when it is done. That way the controller is notified that the data has been downloaded and can refresh.
I don't know if this is the best way to do this, but so far it's working fine for me :-)
To give some more details, in addition to the selector of the method to call when the background task has loaded the data, I also and it a selector of a method on the controller which does the loading. That way the background task manages whats going on, but the view controller provides the data specific code.
Here's there viewDidAppear code:
- (void) viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
if (reloadData) {
BackgroundTask *task = [[BackgroundTask alloc] initWithMethod:#selector(loadData) onObject:self];
task.superView = self.view.superview;
task.notifyWhenFinishedMethod = #selector(loadFinished);
[task start];
[task release];
}
}
The background task has an optional superView because it will add a new UIView to it containing an activity indicator.
BackgroundTask.m looks like this:
#implementation BackgroundTask
#synthesize superView;
#synthesize longRunningMethod;
#synthesize notifyWhenFinishedMethod;
#synthesize obj;
- (BackgroundTask *) initWithMethod:(SEL)aLongRunningMethod onObject:(id)aObj {
self = [super init];
if (self != nil) {
self.longRunningMethod = aLongRunningMethod;
self.obj = aObj;
}
return self;
}
- (void) start {
// Fire into the background.
NSThread *thread = [[NSThread alloc] initWithTarget:self selector:#selector(execute:)object:nil];
thread.name = #"BackgroundTask thread";
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(taskFinished:) name:NSThreadWillExitNotification object:thread];
[thread start];
[thread release];
}
- (void) execute:(id)anObject {
// New thread = new pool.
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
if (self.superView != nil) {
busyIndicatorView = [[BusyIndicator alloc] initWithSuperview:self.superView];
[busyIndicatorView performSelectorOnMainThread:#selector(addToSuperView)withObject:nil waitUntilDone:YES];
}
// Do the work on this thread.
[self.obj performSelector:self.longRunningMethod];
if (self.superView != nil) {
[busyIndicatorView performSelectorOnMainThread:#selector(removeFromSuperView)withObject:nil waitUntilDone:YES];
}
[pool release];
}
- (void) taskFinished:(NSNotification *)notification {
[[NSNotificationCenter defaultCenter] removeObserver:self name:NSThreadWillExitNotification object:notification.object];
[self performSelectorOnMainThread:#selector(notifyObject)withObject:nil waitUntilDone:NO];
}
- (void) notifyObject {
// Tell the main thread we are done.
if (self.notifyWhenFinishedMethod != nil) {
[self.obj performSelectorOnMainThread:self.notifyWhenFinishedMethod withObject:nil waitUntilDone:NO];
}
}
- (void) dealloc {
self.notifyWhenFinishedMethod = nil;
self.superView = nil;
self.longRunningMethod = nil;
self.obj = nil;
[super dealloc];
}
#end
Finally as I said I put up a activity indicator. I have a xib which contains a 50% transparent blue background with an activity indicator in the middle. There is a controller for it which has this code:
#implementation BusyIndicator
#synthesize superView;
#synthesize busy;
- (BusyIndicator *) initWithSuperview:(UIView *)aSuperView {
self = [super initWithNibName:#"BusyIndicator" bundle:nil];
if (self != nil) {
self.superView = aSuperView;
}
return self;
}
- (void) addToSuperView {
// Adjust view size to match the superview.
[self.superView addSubview:self.view];
self.view.frame = CGRectMake(0,0, self.superView.frame.size.width, self.superView.frame.size.height);
//Set position of the indicator to the middle of the screen.
int top = (int)(self.view.frame.size.height - self.busy.frame.size.height) / 2;
self.busy.frame = CGRectMake(self.busy.frame.origin.x, top, self.busy.frame.size.width, self.busy.frame.size.height);
[self.busy startAnimating];
}
- (void) removeFromSuperView {
[self.busy stopAnimating];
[self.view removeFromSuperview];
}
- (void) dealloc {
self.superView = nil;
[super dealloc];
}
#end
Hoep this helps.