I want to write some code to make the UILabel text updates whenever the text gets changed. I am writing a small demo like:
- (IBAction)ButtonPressed:(id)sender {
for(int i = 0; i < 100000; ++i)
{
[self.Label setText:[NSString stringWithFormat:#"%d",i]];
[self.Label setNeedsDisplay];
}
}
When I click the button, the label only changes once to 99999, but I expect it to display 99999 times from 0 to 99999. Anyone has an idea why the code is not working?
Thanks in advance!
setNeedsDisplay tells the system that your view wants to be drawn, but it doesn't force it to happen. The view will be redrawn on the next draw cycle, which is happening after the for loop completes. If you want all 100,000 changes to be visible, you'll have to delay the label updates by a human-perceptible amount.
The above answer is correct, but to elaborate, if you do want to update the content of the label visibly, you can try the following
- (IBAction)ButtonPressed:(id)sender {
for(int i = 0; i < 100000; ++i)
{
double delayInSeconds = 0.01 * i;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
[self.Label setText:[NSString stringWithFormat:#"%d",i]];
[self.Label setNeedsDisplay];
});
}
}
For your purposes though, this is probably irrelevant. A more tactile approach would be to store a number of times the button has been pressed in an instance variable, and increment it each time it is touched, and set the label value appropriately.
Related
I am a little confused about something I was just trying for fun. I have written a little method called animateBars_V1 which uses an array of UIImageViews and alters the height of each UIImageView to show a changing set of coloured bars.
- (void)animateBars_V1 {
srandom(time(NULL));
for(UIImageView *eachImageView in [self barArray]) {
NSUInteger randomAmount = kBarHeightDefault + (random() % 100);
CGRect newRect;
CGRect barRect = [eachImageView frame];
newRect.size.height = randomAmount;
newRect.size.width = barRect.size.width;
newRect.origin.x = barRect.origin.x;
newRect.origin.y = barRect.origin.y - (randomAmount - barRect.size.height);
[eachImageView setFrame:newRect];
}
}
This works fine, I then added a UIButton with a UIAction for when the button is pressed. Each time the button is pressed animateBars_V1 is called and the coloured bars update.
- (IBAction)buttonPressed {
for(int counter = 0; counter<5; counter++) {
[self animateBars_V1];
NSLog(#"COUNTER: %d", counter);
}
}
My question is just for fun I decided that each time the button is pressed I would call animateBars_V1 5 times. What happens is that the bars don't change until after the loop has exited. This results in:
Screen as per storyboard
COUNTER: 0
COUNTER: 1
COUNTER: 2
COUNTER: 3
COUNTER: 4
Screen Updates
Is this the correct behaviour? I don't need a fix or workaround as this was just for fun, I was more curious what was happening for future reference.
If you are calling animateBars_V1 multiple times within a loop, the frames of the bars do get set multiple times, but before they can be rendered, animateBars_V1 gets called again, and the frames are set to a new position/size.
The call to render (drawRect: and related methods) doesn't occur until after the loop is finished - since it is an IBAction, it is by necessity called in the main thread, which means that all rendering is blocked until the code is completed.
There are of course several solutions to this. A simple method to do the multi-animation thing is to use UIView animateWithDuration:animations:completion: in the following manner:
- (IBAction)buttonPressed {
[self animateBarsWithCount:5];
}
- (void)animateBarsWithCount:(int)count
{
[UIView animateWithDuration:.25f animations:^{
[self animateBars_V1];
}completion:^(BOOL finished){
[self animateBarsWithCount:count - 1];
}];
}
//animateBars_V1 not repeated
Of course, if you simply wanted to run the animation one time, (but actually animated) you should do it like this:
- (IBAction)buttonPressed {
[UIView animateWithDuration:.25f animations:^{
[self animateBars_V1];
} completion:nil];
}
CrimsonDiego is right
you can try to delay each call with this:
- (IBAction)buttonPressed {
for(int counter = 0; counter<5; counter++) {
float ii = 1.0 * counter / 10;
[self performSelector:#selector(animateBars_V1) withObject:nil afterDelay:ii];
// [self animateBars_V1];
NSLog(#"COUNTER: %d", counter);
}
}
The problem is here
for(int counter = 0; counter<5; counter++) {
[self animateBars_V1];
NSLog(#"COUNTER: %d", counter);
}
This for loop is executed in nano seconds and your eye is not able to catch up that change as eye can detect only 1/16th of a second.
For testing what can run this code in a timer that runs five time.
Edited
Removed sleep call as it will sleep the main thread and everything will stop. So use Timer here
UPDATE
ViewController is not destroyed, new ViewController is not created. This:
TimerViewController * timerViewController = (TimerViewController *)[segue destinationViewController];
does not create a new instance. However, this
TimerViewController *timerViewController = [self.storyboard instantiateViewControllerWithIdentifier:#"theID"];
does. So a new instance is now being used, but the same problem.
END UPDATE
I have a simple "analog digital timer" where the minutes and seconds animate smoothly to emulate the turning of a number wheel. This is simply a ParentViewController with a list of times, selecting a time performs a segue to the TimerViewController. The TimerViewController uses a recursive UIView animation to simulate the countdown of a clock. This works well.
I want the user to be able to transition to the next timer in the list without having to go back to the ParentViewController in order to select it. This does not work well.
I've tried many variations, the basic pattern is for TimerViewController to ask its delegate (ParentViewController) to pop it and then to seque again to the TimerViewController using the next time from the list of times. The initial animation never terminates, the initial TimerViewController instance never "dies". When I segue to TimerViewController the second time, using what I thought was a new instance, the first animation appears to still be running, the duration of the animation which started at almost 1.0s is off the charts (closer to 0.).
I've tried many different, increasingly desperate, ways to stop the original animation and kill the original instance.
ParentViewController.m
-(void) timerViewControllerDidSwipe (TimerViewController *)controller {
[self.navigationController popViewControllerAnimated:NO];
controller = nil; // ?
[self performSegueWithIdentifier:#"ShowTimer" sender:self];
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([[segue identifier] isEqualToString:#"ShowTimer"])
{
TimerViewController * timerViewController = (TimerViewController *)[segue destinationViewController];
[timerViewController setDelegate:self];
}
TimerViewController.m
-(void) swipe:(id)selector {
// swipe left
stop = YES; // ivar for ^after to not call [self animate]
[self.delegate timerViewControllerDidSwipe:self];
}
-(void) animate {
// anim block here..
void (^after) (BOOL) = ^(BOOL f) {
if (duration % 60 == 0 && duration >= 60) {
if (minutesAlt.center.y < minutes.center.y)
{
CGPoint a = minutes.center;
a.y -= 2 * displacement;
minutes.center = a;
minutes.text = [NSString stringWithFormat:#"%02d", (duration / 60) -1];
}
else
{
CGPoint a = minutesAlt.center;
a.y -= 2 * displacement;
minutesAlt.center = a;
minutesAlt.text = [NSString stringWithFormat:#"%02d", (duration / 60) -1];
}
}
if (duration == 0)
{
// end
}
else if (secondsAlt.center.y < seconds.center.y)
{
CGPoint a = seconds.center;
a.y -= 2 * displacement;
seconds.center = a;
duration--;
seconds.text = [NSString stringWithFormat:#"%02d",duration % 60];
if (!stop) {[self animate];}
}
else
{
CGPoint a = secondsAlt.center;
a.y -= 2 * displacement;
duration--;
secondsAlt.center = a;
secondsAlt.text = [NSString stringWithFormat:#"%02d", duration % 60];
if (!stop) {[self animate];}
}
};
[UIView animateWithDuration:0.50
delay:0.50
options:UIViewAnimationOptionCurveLinear
animations:anim
completion:after];
}
Any help greatly appreciated.
Fixed here in a related question. It was a simple syntax error (that took me weeks to find).
I'm relatively new to Objective-C so this might be really simple to do: I have a text box in my application that displays an ammo count, so each time the user taps a fire button the number in the text box will go down by one (12 > 11 > 10, etc) to 0. I have tried using for and if statements, but they are not working (I may have used incorrect syntax). This is what I'm using right now, but obviously I need the
- (IBAction)fire {
[ammoField setText:#"11"];
}
- (IBAction)reload {
[ammoField setText: #"12"];
}
The simplest way would be to convert the text to a number, decrement that and the reset the text, i.e. replace the code in the fire method with:
NSInteger ammoCount = [ammoField.text integerValue];
ammoCount--;
ammoField.text = [NSString stringWithFormat:#"%d", ammoCount];
But don't do this, it will make baby Steve Jobs cry.
A better way would be to add a new variable to the class of type UIInteger that tracks the the number of bullets, i.e.:
// in interface
NSInteger _ammoCount;
...
// in implementation
- (IBAction)fire {
_ammoCount--;
if (_ammoCount <= 0) {
_ammoCount = 0;
fireButton.enabled = NO;
}
[ammoField setText: [NSString stringWithFormat:#"%d", _ammoCount]];
}
- (IBAction)reload {
_ammoCount = 12;
[ammoField setText: [NSString stringWithFormat:#"%d", _ammoCount]];
fireButton.enabled = YES;
}
Oh, and don't forget to call reload at some point early on to ensure _ammoCount and ammoField get initialised.
Set Instance Integer
int x;
set value of it
x = 12;
do change in method
- (IBAction)fire {
[ammoField setText:[NSString stringWithFormat:#"%i",x]];
x--;
}
set the value of count in viewdidload with an int variable
fire method decrease the count by 1
and reload method to return value to 12
log or use values accordingly
Try this:-
int i;
-(void)ViewDidLoad
{
i=12;
}
- (IBAction)fire
{
[ammoField setText:[NSString stringWithFormat:#"%d",i]];
i--;
}
- (IBAction)reload {
i = 12;
[ammoField setText: [NSString stringWithFormat:#"%d", i]];
}
Hope it will work for you. Thanks :)
Suppose I run this code:
__block int step = 0;
__block dispatch_block_t myBlock;
myBlock = ^{
if(step == STEPS_COUNT)
{
return;
}
step++;
dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_SEC / 2);
dispatch_after(delay, dispatch_get_current_queue(), myBlock);
};
dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_SEC / 2);
dispatch_after(delay, dispatch_get_current_queue(), myBlock);
The block is invoked once from outside. When the inner invocation is reached, the program crashes without any details. If I use direct invocations everywhere instead of GCD dispatches, everything works fine.
I've also tried calling dispatch_after with a copy of the block. I don't know if this was a step in the right direction or not, but it wasn't enough to make it work.
Ideas?
When trying to solve this problem, I found a snippet of code that solves much of the recursive block related issues. I have not been able to find the source again, but still have the code:
// in some imported file
dispatch_block_t RecursiveBlock(void (^block)(dispatch_block_t recurse)) {
return ^{ block(RecursiveBlock(block)); };
}
// in your method
dispatch_block_t completeTaskWhenSempahoreOpen = RecursiveBlock(^(dispatch_block_t recurse) {
if ([self isSemaphoreOpen]) {
[self completeTask];
} else {
double delayInSeconds = 0.3;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), recurse);
}
});
completeTaskWhenSempahoreOpen();
RecursiveBlock allows for non-argument blocks. It can be rewritten for single or multiple argument blocks. The memory management is simplified using this construct, there is no chance of a retain cycle for example.
My solution was derived entirely from Berik's, so he gets all the credit here. I just felt that a more general framework was needed for the "recursive blocks" problem space (that I haven't found elsewhere), including for the asynchronous case, which is covered here.
Using these three first definitions makes the fourth and fifth methods - which are simply examples - possible, which is an incredibly easy, foolproof, and (I believe) memory-safe way to recurse any block to arbitrary limits.
dispatch_block_t RecursiveBlock(void (^block)(dispatch_block_t recurse)) {
return ^() {
block(RecursiveBlock(block));
};
}
void recurse(void(^recursable)(BOOL *stop))
{
// in your method
__block BOOL stop = NO;
RecursiveBlock(^(dispatch_block_t recurse) {
if ( !stop ) {
//Work
recursable(&stop);
//Repeat
recurse();
}
})();
}
void recurseAfter(void(^recursable)(BOOL *stop, double *delay))
{
// in your method
__block BOOL stop = NO;
__block double delay = 0;
RecursiveBlock(^(dispatch_block_t recurse) {
if ( !stop ) {
//Work
recursable(&stop, &delay);
//Repeat
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delay * NSEC_PER_SEC)), dispatch_get_main_queue(), recurse);
}
})();
}
You'll note that in the following two examples that the machinery of interacting with the recursion mechanism is extremely lightweight, basically amounting to having to wrap a block in recurse and that block must take a BOOL *stop variable, which should be set at some point to exit recursion (a familiar pattern in some of the Cocoa block iterators).
- (void)recurseTo:(int)max
{
__block int i = 0;
void (^recursable)(BOOL *) = ^(BOOL *stop) {
//Do
NSLog(#"testing: %d", i);
//Criteria
i++;
if ( i >= max ) {
*stop = YES;
}
};
recurse(recursable);
}
+ (void)makeSizeGoldenRatio:(UIView *)view
{
__block CGFloat fibonacci_1_h = 1.f;
__block CGFloat fibonacci_2_w = 1.f;
recurse(^(BOOL *stop) {
//Criteria
if ( fibonacci_2_w > view.superview.bounds.size.width || fibonacci_1_h > view.superview.bounds.size.height ) {
//Calculate
CGFloat goldenRatio = fibonacci_2_w/fibonacci_1_h;
//Frame
CGRect newFrame = view.frame;
newFrame.size.width = fibonacci_1_h;
newFrame.size.height = goldenRatio*newFrame.size.width;
view.frame = newFrame;
//Done
*stop = YES;
NSLog(#"Golden Ratio %f -> %# for view", goldenRatio, NSStringFromCGRect(view.frame));
} else {
//Iterate
CGFloat old_fibonnaci_2 = fibonacci_2_w;
fibonacci_2_w = fibonacci_2_w + fibonacci_1_h;
fibonacci_1_h = old_fibonnaci_2;
NSLog(#"Fibonnaci: %f %f", fibonacci_1_h, fibonacci_2_w);
}
});
}
recurseAfter works much the same, though I won't offer a contrived example here. I am using all three of these without issue, replacing my old -performBlock:afterDelay: pattern.
It looks like there are no problem except delay variable. The block uses always the same time that is generated at line 1. You have to call dispatch_time every time if you want to delay dispatching the block.
step++;
dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_SEC / 2);
dispatch_after(delay, dispatch_get_current_queue(), myBlock);
};
EDIT:
I understand.
The block is stored in stack by the block literal. myBlock variable is substituted for the address of the block in stack.
First dispatch_after copied the block from myBlock variable that is the address in stack. And this address is valid at this time. The block is in the current scope.
After that, the block is scoped out. myBlock variable has invalid address at this time. dispatch_after has the copied block in heap. It is safe.
And then, second dispatch_after in the block tries to copy from myBlock variable that is invalid address because the block in stack was already scoped out. It will execute corrupted block in stack.
Thus, you have to Block_copy the block.
myBlock = Block_copy(^{
...
});
And don't forget Block_release the block when you don't need it any more.
Block_release(myBlock);
Opt for a custom dispatch source.
dispatch_queue_t queue = dispatch_queue_create( NULL, DISPATCH_QUEUE_SERIAL );
__block unsigned long steps = 0;
dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_DATA_ADD, 0, 0, queue);
dispatch_source_set_event_handler(source, ^{
if( steps == STEPS_COUNT ) {
dispatch_source_cancel(source);
return;
}
dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_SEC / 2);
dispatch_after(delay, queue, ^{
steps += dispatch_source_get_data(source);
dispatch_source_merge_data(source, 1);
});
});
dispatch_resume( source );
dispatch_source_merge_data(source, 1);
I think you have to copy the block if you want it to stick around (releasing it when you don't want it to call itself anymore).
I have to update a small amount of text in a scrolling UITextView. I'll only be inserting a character where the cursor currently is, and I'll be doing this on a press of a button on my navigation bar.
My problem is that whenever I call the setText method of the text view, it jumps to the bottom of the text. I've tried using contentOffset and resetting the selectedRange but it doesn't work! Here's my example:
// Remember offset and selection
CGPoint contentOffset = [entryTextView contentOffset];
NSRange selectedRange = [entryTextView selectedRange];
// Update text
entryTextView.text = entryTextView.text;
// Try and reset offset and selection
[entryTextView setContentOffset:contentOffset animated:NO];
[entryTextView setSelectedRange: selectedRange];
Is there any way you can update the text without any scroll movement at all... as if they'd just typed something on the keyboard?
Edit:
I've tried using the textViewDidChange: delegate method but it's still not scrolling up to the original location.
- (void)textViewDidChange:(UITextView *)textView {
if (self.programChanged) {
[textView setSelectedRange:self.selectedRange];
[textView setContentOffset:self.contentOffset animated:NO];
self.programChanged = NO;
}
}
- (void)changeButtonPressed:(id)sender {
// Remember position
self.programChanged = YES;
self.contentOffset = [entryTextView contentOffset];
self.selectedRange = [entryTextView selectedRange];
// Update text
entryTextView.text = entryTextView.text;
}
If you use iPhone 3.0 or later, you can solve this problem:
textView.scrollEnabled = NO;
//You should know where the cursor will be(if you update your text by appending/inserting/deleting you can know the selected range) so keep it in a NSRange variable.
Then update text:
textView.text = yourText;
textView.scrollEnabled = YES;
textView.selectedRange = range;//you keep before
It should work now (no more jumping)
Regards
Meir Assayag
Building on Meir's suggestion, here's code that removes the selection programmatically (yes I know there's a selection menu button that does it too, but I'm doing something a bit funky) without scrolling the text view.
NSRange selectedRange = textView.selectedRange;
textView.scrollEnabled = NO;
// I'm deleting text. Replace this line with whatever insertions/changes you want
textView.text = [textView.text
stringByReplacingCharactersInRange:selectedRange withString:#""];
selectedRange.length = 0;
// If you're inserting text, you might want to increment selectedRange.location to be
// after the text you inserted
textView.selectedRange = selectedRange;
textView.scrollEnabled = YES;
This decision works for iOS 8:
let offset = textView.contentOffset
textView.text = newText
textView.layoutIfNeeded()
textView.setContentOffset(offset, animated: false)
It is necessary to call exactly setContentOffset:animated: because only this will cancel animation. textView.contentOffset = offset will not cancel the animation and will not help.
The following two solutions don't work for me on iOS 8.0.
textView.scrollEnabled = NO;
[textView.setText: text];
textView.scrollEnabled = YES;
and
CGPoint offset = textView.contentOffset;
[textView.setText: text];
[textView setContentOffset:offset];
I setup a delegate to the textview to monitor the scroll event, and noticed that after my operation to restore the offset, the offset is reset to 0 again. So I instead use the main operation queue to make sure my restore operation happens after the "reset to 0" option.
Here's my solution that works for iOS 8.0.
CGPoint offset = self.textView.contentOffset;
self.textView.attributedText = replace;
[[NSOperationQueue mainQueue] addOperationWithBlock: ^{
[self.textView setContentOffset: offset];
}];
No of the suggested solutions worked for me. -setContentOffset:animated: gets triggered by -setText: 3 times with animated YES and a contentOffset of the end (minus the default 8pt margin of a UITextView). I wrapped the -setText: in a guard:
textView.contentOffsetAnimatedCallsDisabled = YES;
textView.text = text;
textView.contentOffsetAnimatedCallsDisabled = NO;
In a UITextView subclass in -setContentOffset:animated: put
if (contentOffsetAnimatedCallsDisabled) return; // early return
among your other logic. Don’t forget the super call. This works.
Raphael
In order to edit the text of a UITextView, you need to update it's textStorage field:
[_textView.textStorage beginEditing];
NSRange replace = NSMakeRange(10, 2); //enter your editing range
[_textView.textStorage replaceCharactersInRange:replace withString:#"ha ha$ "];
//if you want to edit the attributes
NSRange attributeRange = NSMakeRange(10, 5); //enter your editing attribute range
[_textView.textStorage addAttribute:NSBackgroundColorAttributeName value:[UIColor greenColor] range:attributeRange];
[_textView.textStorage endEditing];
Good luck
in iOS 7. There seams to be a bug with sizeThatFits and having linebreaks in your UITextView the solution I found that works is to wrap it by disabling scrolling. Like this:
textView.scrollEnabled = NO;
CGSize newSize = [textView sizeThatFits:CGSizeMake(fixedWidth, MAXFLOAT)];
textView.scrollEnabled = YES;
and weird jumping has been fixed.
I hit a a similar, if not the same, problem in IOS9. Changing the characteristics of some text to, say, BOLD caused the view to scroll the selection out of sight. I sorted this by adding a call to scrollRangeToVisible after the setSelectedRange:
[self setSelectedRange:range];
[self scrollRangeToVisible:range];
Take a look at the UITextViewDelegate, I believe the textViewDidChangeSelection method may allow you to do what you need.
Old question but I had the same issue with iOS 7 app. Requires changing the contentOffset a little bit after the run loop. Here is a quick idea.
self.clueString = [self.level clueText];
CGPoint point = self.clueText.contentOffset;
self.clueText.attributedText = self.clueString;
double delayInSeconds = 0.001; // after the run loop update
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
[self.clueText setContentOffset:point animated:NO];
});
Finally try this, checked on iOS 10
let offset = textView.contentOffset
textView.attributedText = newValue
OperationQueue.main.addOperation {
self.textView.setContentOffset(offset, animated: false)
}
Not so elegant solution- but it works so who cares:
- (IBAction)changeTextProgrammaticaly{
myTextView.text = #"Some text";
[NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:#selector(rewindOffset) userInfo:nil repeats:NO];
}
- (void)rewindOffset{
[myTextView setContentOffset:CGPointMake(0,0) animated: NO];
}
I found a solution that works reliably in iOS 6 and 7 (and probably earlier versions). In a subclass of UITextView, do the following:
#interface MyTextView ()
#property (nonatomic) BOOL needToResetScrollPosition;
#end
#implementation MyTextView
- (void)setText:(NSString *)text
{
[super setText:text];
self.needToResetScrollPosition = YES;
}
- (void)layoutSubviews
{
[super layoutSubviews];
if (self.needToResetScrollPosition) {
self.contentOffset = CGPointMake(0, 0);
self.needToResetScrollPosition = NO;
}
}
None of the other answers work in iOS 7 because it will adjust the scroll offsets at display time.