Open iPhone SDK: Building a UIProgressBar
Progress bars allow end-users to anticipate wait times. They present bars that fill from left to right. These bars indicate the degree to which a task has finished. Progress bars work best for long waits where providing state feedback allows your users to retain the feel of control.
To create a progress bar, allocate it and set its frame. To use the bar, issue setProgress:. This takes one argument, a floating point number that ranges between 0.0 (no progress) and 1.0 (finished). Progress bars come in two styles: basic white (style 0) or light gray (style 1). setStyle: chooses the kind your prefer.
Unlike the other kinds of progress indicators, it’s completely up to you to show and hide the progress bar’s view. I like adding progress bars to alert sheets. This simplifies both bringing them onto the screen and dismissing them. Another advantage is that when alert sheets display, the rest of the screen dims. This forces a modal presentation as your task progresses. Users cannot interact with the GUI until you dismiss the alert.
@implementation SampleApp
#define STYLE 0
- (void) handleTimer: (id) timer
{
amt += 1;
[progbar setProgress: (amt / 20.0)];
if (amt > 20.0) {[alert dismiss]; [timer invalidate];}
}
- (void) applicationDidFinishLaunching: (id) unused
{
UIImage *img = [UIImage applicationImageNamed:@"Default.png"];
UIImageView *imgView = [[UIImageView alloc] initWithImage:img];
struct CGRect rect = [UIHardware fullScreenApplicationContentRect];
UIWindow *window = [[UIWindow alloc] initWithContentRect: rect];
[window orderFront: self];
[window makeKey: self];
[window setContentView: imgView];
// Create an otherwise-empty alert sheet
alert = [[UIAlertSheet alloc]
initWithTitle:@"Updating Database"
buttons:NULL
defaultButtonIndex:0
delegate:self
context:self];
[alert setBodyText:@"Please wait...\n\n\n\n"];
// Create the progress bar and add it to the alert
progbar = [[UIProgressBar alloc] initWithFrame:
CGRectMake(50.0f, 70.0f, 220.0f, 90.0f)];
[alert addSubview:progbar];
[progbar setStyle: STYLE];
[alert presentSheetInView:imgView];
// This timer takes the place of a real task
amt = 0.0;
id timer = [NSTimer scheduledTimerWithTimeInterval: 0.5
target: self
selector: @selector(handleTimer:)
userInfo: nil
repeats: YES];
}
@end
Categories
Mac
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