![\"image\"](\"http:\/\/www.smartersoftware.de\/wordpress\/wp-content\/pics\/863fbeb5a952_7DA0\/image_thumb_4.png\" "\\"image\\"")
<\/a><\/p>\nIt consists of a few labels (for the title, the number of records and the remaining time) and a ProgressBar. The trickiest thing here is the positioning of all the items on the screen. (I\u2019m sure the code I have is a bit clumsy and can be improved. Suggestions are welcome, please add a comment.)<\/p>\n
\/\/add top Label\r\ntopLabel = [[UILabel alloc] initWithFrame:\r\n CGRectMake(0, gutter, width-4*gutter, 20.)];\r\n[topLabel setCenter: CGPointMake(center.x, center.y - 30.)];\r\n[topLabel setText: @"[Being busy]"];\r\n[topLabel setTextAlignment:UITextAlignmentCenter];\r\n[self addSubview: topLabel];\r\n\r\n\/\/add Progress Bar\r\nprogbar = [[UIProgressView alloc] initWithFrame:\r\n CGRectMake(0, 0, width-4*gutter, 20.)];\r\n[progbar setCenter: center];\r\n[progbar setProgress: 0.];\r\n[progbar setProgressViewStyle:UIProgressViewStyleBar];\r\n[self addSubview: progbar]; \r\n\r\n\/\/add progress Label\r\nprogLabel = [[UILabel alloc] initWithFrame:\r\n CGRectMake(0, 0, width-4*gutter , 20.)];\r\n[progLabel setCenter:CGPointMake(center.x, center.y + 10.)];\r\n[progLabel setTextAlignment:UITextAlignmentCenter];\r\n[progLabel setText: [NSString stringWithFormat: @"At record %i of %i", currentValue, maxValue]];\r\n[self addSubview: progLabel]; \r\n\r\n\/\/ add remaining time label\r\nremainingLabel = [[UILabel alloc] initWithFrame:\r\n CGRectMake(0, 0, width-4*gutter , 20.)];\r\n[remainingLabel setCenter:CGPointMake(center.x, center.y + 30.)];\r\n[remainingLabel setTextAlignment:UITextAlignmentCenter];\r\n[remainingLabel setText: @"Calculating remaining time ..."];\r\n[self addSubview: remainingLabel]; <\/pre>\nIt is displayed as a little \u201cdialog box\u201d on the screen and \u201cdims\u201d the view that it is called from by using a semi-transparent background:<\/p>\n
[self setBackgroundColor: [UIColor colorWithRed:204.\/255 green:213.\/255 blue:216.\/255 alpha:0.5]];<\/pre>\nThe ProgressView can be updated by calling the \u201csetCurrentValue\u201d method which then updates all the labels and the progress bar:<\/p>\n
-(void) setCurrentValue:(NSInteger)newCurrentValue {\r\n currentValue = newCurrentValue;\r\n if (currentValue % stepValue == 0) { \/\/% is modulus\r\n [progLabel setText: [NSString stringWithFormat: @"At record %i of %i", currentValue, maxValue]];\r\n [progbar setProgress: (float) (currentValue) \/ maxValue];\r\n \r\n if (currentValue > 0 && abs([startTime timeIntervalSinceNow]) > 0) {\r\n int remaining = trunc (abs([startTime timeIntervalSinceNow]) \r\n * (maxValue - currentValue) \/ currentValue);\r\n [remainingLabel setText: [NSString stringWithFormat: @"About %i seconds remaining", remaining]];\r\n } else {\r\n [remainingLabel setText: @"Calculating remaining time ..."];\r\n }\r\n }\r\n}<\/pre>\nAll that\u2019s left to do, is to open the view at the start of the long-running operation using addSubview: and then update the ProgressView by calling setCurrentValue:. When the operation is done, we just remove the ProgressView using removeFromSuperview.<\/p>\n
This almost works .. the ProgressView is displayed at the start and removed at the end of the operation, but then it is not updated during the operation \u2013 which means no feedback to the user and it looks like the program crashed.<\/p>\n
Making it work using threading<\/h2>\n
The reason for this behavior is that the screen is not updated while the operation executes \u2013 I\u2019m not exactly sure when the update would occur (unless when the whole operation is over). This is because the simple program is unthreaded, i.e. there is no thread that is available to update the screen. In VisualBasic there is the expression \u201cDo Events\u201d which basically turns control over to the OS to process screen updates, user inputs etc. There does not seem to be an equivalent expression in iOS, instead we have to delve a bit into threading to separate between the screen updates and the calculation.<\/p>\n
Setting up the threading environment<\/h3>\n
In earlier versions of iOS it was quite a lot of work to set up the threading environment. Since version [???] this has been made a lot easier by providing NSOperationQueue and NSInvocationOperation. Now all that is left to is:<\/p>\n
NSOperationQueue *queue = [NSOperationQueue new];\r\nNSInvocationOperation *operation = \r\n [[NSInvocationOperation alloc] initWithTarget:self\r\n selector:@selector()\r\n object:nil];\r\n[queue addOperation:operation];\r\n[operation release];<\/pre>\nThe NSOperationQueue basically set ups the threading environment, so that as soon as an operation is added to the queue, the execution is started in a secondary thread. <\/p>\n
Updating the ProgressView<\/h3>\n
This secondary thread is then executing the long running operation, while the primary thread can still update the screen. Within our operation we can trigger the screen update in the main thread:<\/p>\n
[self performSelectorOnMainThread:@selector(updateProgress) \r\n withObject: nil waitUntilDone:YES];<\/pre>\nI\u2019ve had some problems passing an object using the \u201cwithObject:\u201d selector, probably because I was using memory that was only available to the secondary thread. (Probably because it was allocated by the secondary thread.) Instead, I was able to use a property of the view that created the secondary thread. <\/p>\n
Tearing down<\/h3>\n
All that was left to do was to remove the view when the operation is done. This is achieved by calling<\/p>\n
[self performSelectorOnMainThread:@selector(calculationDone) withObject:nil waitUntilDone:YES];<\/pre>\nAgain, this calls the main thread to notify that the calculation is done and that the ProgressView can be removed.<\/p>\n
Summary<\/h2>\n
We\u2019ve managed to build a good looking, informative ProgressView. In addition to implementing the code to display, update and remove the view, we also had to make sure that the ProgressView is updated on the screen by creating and using a secondary thread. The additional code required for the threading was quite small, and it was able to use the original, unchanged code for the ProgressView.<\/p>\n","protected":false},"excerpt":{"rendered":"
When you are doing some longer running operation in a program, you want to give some feedback to the user. This blog post looks at some ways on how to do this in iOS. I\u2019m using my ongoing work on my next iPhone app \u201cSmarterContacts\u201d [include link] which will find and eliminate duplicates in your […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[32],"tags":[],"class_list":["post-199","post","type-post","status-publish","format-standard","hentry","category-ios"],"_links":{"self":[{"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/posts\/199","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/comments?post=199"}],"version-history":[{"count":1,"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/posts\/199\/revisions"}],"predecessor-version":[{"id":200,"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/posts\/199\/revisions\/200"}],"wp:attachment":[{"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/media?parent=199"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/categories?post=199"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.smartersoftware.de\/wordpress\/wp-json\/wp\/v2\/tags?post=199"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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