Aplogies, but this is another newbie iPhone/Objective-C question.
I'm working on my first iPhone app which is a simple RPN calculator. I have a table displaying the contents of the stack, and now I'd like to fine tune the display a little bit.
I would like for the last entry in the stack to display at the bottom of the table, with the text right aligned. The right alignment was easy with
cell.textLabel.textAlignment = UITextAlignmentRight;
and I can make the table peg the last entry to the bottom of the view with this code:
NSIndexPath *scrollIndexPath = [NSIndexPath indexPathForRow:(stackSize - 1) inSection:0];
[tableView scrollToRowAtIndexPath:scrollIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];
which works great but only when there are more entries on the stack than will fit in the view. When the stack has few entries, they're still aligned to the top of the view.
I've played a bit with altering the height of the cell for the first stack entry such that the first cell fills the whole view and shrinks as new cells are added until there are enough stack entries to fill the view, at which point the cell height is left alone. This seemed promising, but I'm having some trouble getting the "big" cell to bottom align the label. (It's vertical center aligned, by default.)
As I was hacking away at the bottom alignment thing, I began to wonder if I'm making this more complicated than it needs to be. Any thoughts?
I don't know if this is kosher, but you can use view transforms to rotate the table 180° and then rotate each cell 180°. I use this trick to create sideways tables (90° instead of 180°) on an app I'm writing.
Another approach is to resize the table view as you add or remove rows. You update the height and move the table view accordingly. Something like this looks quite OK:
- (void)resizeTableView {
CGFloat tableViewHeight = [self tableView:self.tableView numberOfRowsInSection:0] * self.tableView.rowHeight;
// remember to check the height !!
CGRect frame = self.tableView.frame;
frame.size.height = tableViewHeight;
frame.origin.y = BOTTOM_OF_VIEW - tableViewHeight;
[UIView animateWithDuration:0.3 animations:^{
[self.tableView setFrame:frame];
}];
}
If you are using the default animations for insert and delete, remember to set them to UITableViewRowAnimationNone, otherwise it looks strange.
Related
For example in Tweetbot's iPhone app. When you open up the app and new tweets come in, it will just be appended to the top of the UIScrollView and the current tweet you see did not get refreshed. How can I achieve the same thing effect?. Say I have a UIScrollView with a UIView added to the UIScrollView starting at origin 10,10.
I then downloaded a few items and I want to put it at 10,10.. so I basically need to shift this old item at 10,10 down right? If I do so then during that shifting user's will see it shifted, which is not the effect I want. Where as in Tweetbot's app it seems that nothing is being shifted around, it's just that you grow the area above the 10,10 and append new stuff's there.
How do I do this?
Basically I wanted to implement the insertRowAtIndexPath in a UIScrollView.
Will restate the question this way: how to add content to the top of a UIScrollView without moving the content that's already there (relative to it's current offset).
If this is the right question, the right answer is to do the add and shift down just as you suggested, but then scroll by the same height as added content, giving the illusion that the old content didn't move.
- (void)insertRowAtTop {
// not showing insert atIndexPath because I don't know how you have your subviews indexed
// inserting at the top, we can just shift everything down. you can extend this idea to
// the middle but it requires that you can translate from rows to y-offsets to views
// shift everything down
for (UIView *view in self.scrollView.subviews) {
if ([view isKindOfClass:[MyScrollViewRow self]]) {
MyScrollViewRow *row = (MyScrollViewRow *)view; // all this jazz so we don't pick up the scroll thumbs
row.frame = CGRectOffset(row.frame, 0.0, kROW_HEIGHT); // this is a lot easier if row height is constant
}
}
MyScrollViewRow *newRow = [[MyScrollViewRow alloc] initWithFrame:CGRectMake(0.0,0.0,320.0,kROW_HEIGHT)];
// init newRow
[self.scrollView addSubview:newRow];
// now for your question. scroll everything so the user perceives that the existing rows remained still
CGPoint currentOffset = self.scrollView.contentOffset
self.scrollView.contentOffset = CGPointMake(currentOffset.x, currentOffset.y + kROW_HEIGHT);
}
If you set the contentOffset without animating there wont be a visible scrolling animation. So if your new view is 200 points tall you can set the origin of the new view at (10,10) and the old view at (10,210) and set the contentOffset of the scroll view to (10,210) you should achieve the effect you intend. You'll also need to increase the contentSize of your scroll view to be big enough for all of the content it contains.
I have a table that I'm doing some special loading for. The user starts scrolled to the bottom. When the user scrolls near the top, I detect this through scroll view delegate methods, and I quickly load some additional content, and populate more of the top part of the list. I want this to look seamless, like an "infinite scroll" upward. To do this, I have to set the content offset, so that the user doesn't see the table "jump" upward. When I scroll slowly, this works perfectly. When I scroll quickly, so that the table is decelerating, the content offset I set is ignored. Here is the code I'm using:
CGFloat oldHeight = self.tableView.contentSize.height;
CGFloat oldOffset = self.tableView.contentOffset.y;
self.tableContentsArray = newTableContentsArray;
[self.tableView reloadData];
CGFloat newHeight = self.tableView.contentSize.height;
CGFloat newOffset = oldOffset + (newHeight - oldHeight);
self.tableView.contentOffset = CGPointMake(0, newOffset);
So if I scroll up quickly with a table 100px high and hit the top while decelerating, I load more data, get a new table height of, say, 250px. I set the offset to 150. However, since it's still decelerating, the Apple code leaves the offset set to 150 for .1 seconds or something, then goes to the next calculated offset for deceleration, and sets the offset to 0, which makes it look to the user like they just skipped 150px of content, and are now at the new top of the list.
Now I'd LOVE to keep the acceleration from the list, so that it keeps going up for a while, slows down, and ends up somewhere around 120px offset, just like you would expect. Question is, how?
If I use [self.tableView setContentOffset: CGPointMake(0, newOffset) animated: NO]; it stops the content offset from being ignored, but stops the list dead.
We had an interesting situation like this at work a few months back. We wanted to use the UITableViewController because of it's caching, loading, and animations, but we wanted it to scroll horizontally (in your case it would be scroll upward). The solution? Rotate the table, then rotate the cells the other direction.
In your case, the code would look like this:
#define degreesToRadian(x) (M_PI * (x) / 180.0) in the header
- (void) viewDidLoad {
[super viewDidLoad];
self.table.transform = CGAffineTransformMakeRotation(degreesToRadian(-180));
...
}
Then rotate the cell, so it appears in the right orientation for the user
- (UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
...
cell.transform = CGAffineTransformMakeRotation(degreesToRadian(180));
}
Now you can postpend your cells like any normal table, and they'll be added on top instead of the bottom.
I am afraid you are trying to do things too complicated without really understanding them.
Do you really have an infitite table or a very long table? I think it would be possible to just tell the table it has 1000000 cells. Each cell is loaded when you need it. And that's basically what you want to do.
I'm fairly new to programming, and I have looked for an answer for a very long time. There are some posts about it, but nothing has solved my problem. I have a UIScrollView view that I get from the nib, everything is ok with this, the content length is good and scrolling works, but it just scrolls on the left side, if I try to scroll on the right side it doesn't scroll..
Here is the code,
- (void)viewDidLoad {
[super viewDidLoad];
NSString *descriptionString = _currentBook.description;
CGSize stringSize = [descriptionString sizeWithFont:[UIFont boldSystemFontOfSize:16] constrainedToSize:CGSizeMake(387, 9999) lineBreakMode:UILineBreakModeWordWrap];
_authorLabel.text = _currentBook.author;
_titleLabel.text = _currentBook.title;
_descriptionLabel.text = [NSString stringWithFormat:#"Description: %#",_currentBook.description];
[(UIScrollView *)self.view setContentSize:CGSizeMake(387, stringSize.height +50)];
}
Thanks in advance!
Its hard to understand the problem since we cant see your nib file, but its better practice to put the scrollView on top the view of the view controller, and connect it to an IBOutlet in your view controller.
In order to find the problem I would get rid of the textfields for testing purposes (I think the constrained 9999 might be a problem but I am not sure) and then print and post the frame of the scrollView and the Content size in runtime.I am betting that you will see some issue with the frame of the uiscrollview.
Thanks,
Ok, after copy-pasting and running some tests, I found out the problem.
The problem is in the wording of the question, your problem is not that the "scroll doesn't work on the right side" (As in: you move your finger up and down on the right side of the screen without triggering a scroll), the problem is that the contents, the label itself is going out of bounds, outside of the visible area of the scrollView, and the right-handed side is not visible.
First of all, you should note that the iphone resolution is 320x480 (640x960 for Retina), so you actually have to work with a smaller width (using 387 width will make it go out of bounds).
Second, take in account the x position of the label itself is also affecting the amount of visible text. With this in mind, a more generic code would be:
- (void)viewDidLoad
{
[super viewDidLoad];
// This number represents the total width of the label that will fit centered in
// the scrollView area.
CGFloat visibleWidth = self.view.frame.width - descriptionLabel.frame.origin.x*2;
// Use the number above to get a more accurate size for the string.
NSString *descriptionString = _currentBook.description;
CGSize stringSize = [descriptionString sizeWithFont:[UIFont boldSystemFontOfSize:16] constrainedToSize:CGSizeMake(visibleWidth, 9999) lineBreakMode:UILineBreakModeWordWrap];
// Fill data (why so many underscores?)
_authorLabel.text = _currentBook.author;
_titleLabel.text = _currentBook.title;
_descriptionLabel.text = [NSString stringWithFormat:#"Description: %#", _currentBook.description];
// Also, why didn't you resize the description label? I'm assuming that you forgot this.
// (Make sure that the descriptionLabel number of lines is 0)
CGRect frame = descriptionLabel.frame;
descriptionLabel.frame.size = stringSize;
// Now set the content size, since you're using the scrollView as the main view of the viewController,
// I'll asume that it's using the whole screen, so I'm gonna use the whole width
// of the screen (that's what UIScreen is for).
[(UIScrollView *)self.view setContentSize:CGSizeMake([UIScreen mainScreen].bounds.size.width, stringSize.height +50)];
}
Finally i've found my problem, I've added a uiview programmatically as a subview to some view and then to this View i've added my scroll view as a subview.. And then it would only scroll in the area of my UIView. It was nonsense to do it like this, still a lack of knowledge..
Thank you all for trying to help!
EDIT - I've worked out what I was originally doing wrong. I was changing the size of the UIScrollView, instead of the pattern subview. I have fixed that, but amended my question with the new problem this has thrown up.
I am making a notes section in my app with a lined-paper effect. The lines are on a separate UIScrollView which responds to scrollViewDidScroll: so the lines and text always move together. My lines are set up like this in viewWillAppear:
CGRect noteLinesRect = CGRectMake(self.view.bounds.origin.x,
self.view.bounds.origin.y,
self.view.bounds.size.width,
noteTextView.contentSize.height+self.view.bounds.size.height);
UIScrollView *anoteXLinesView = [[UIScrollView alloc] initWithFrame:self.view.bounds];
self.noteXLinesView = anoteXLinesView;
[anoteXLinesView release];
LinePatternView *linesPattern = [[LinePatternView alloc] initWithFrame:noteLinesRect];
self.linesPatternView = linesPattern; [linesPattern release];
[self.noteXLinesView addSubview:self.linesPatternView];
[linesPattern release];
CGPoint newOffset = CGPointMake(self.noteTextView.contentOffset.x, noteTextView.contentOffset.y - NOTE_LINES_OFFSET);
self.noteXLinesView.contentOffset = newOffset;
[self.view insertSubview:self.noteXLinesView atIndex:0];
This works fine when the user first looks at a stored note - all the text is nicely underlined. But when they write more text, eventually they get to the bottom of the lines I created in viewWillAppear and are writing on 'blank paper'. So I need my lined-paper pattern to dynamically get bigger and smaller so it is always a bit bigger than the contentSize of my textView. I am trying to do that like this:
-(void)textViewDidChange:(UITextView *)textView
{
self.linesPatternView.frame = CGRectMake( self.linesPatternView.frame.origin.x, //-self.noteTextView.contentOffset.y+NOTE_LINES_OFFSET,
self.linesPatternView.frame.origin.y,
self.linesPatternView.frame.size.width,
noteTextView.contentSize.height+self.view.bounds.size.height );
}
The problem is, although the lined-paper pattern does increase in size, it doesn't add new lines at the bottom. Instead, the pattern stretches out and gets bigger as the view gets bigger. What am I doing wrong?
One of the solutions is to make 3 views, each containing the lines of the size of your scrollview frame on screen. You position the three one underneath the other in the scrollview and monitor the scrollview through its delegate.
When scrolling down you check:
As soon as the topmost one goes offscreen for more than Y pixels you remove it from the scrollview and insert it underneath the bottom one.
When scrolling up you check:
As soon as the bottommost one goes offscreen for more than Y pixels you remove it from the scrollview and insert it above the top one.
Is there a reason you’re not simply using a tiled pattern as your background view’s backgroundColor? UIColor’s +colorWithPatternImage: will let you set a background that’ll tile indefinitely and won’t stretch as your view resizes. If part of the background has to be different—like the top of your paper, for instance—you can just place an image view containing that at the top of your background view.
Fixed! In addition to the changes outlined in my edit to the question above, I just needed to call [self.linesPatternView setNeedsDisplay]; after the resize.
I have a table view which is many cases will only have one or two cells that don't fill the screen. In this case, I would like the cells to sit at the bottom, rather than the top. In other words they should "snap" to the bottom of the tableview.
I can force the table view to scroll them to the bottom like this:
CGPoint bottomOffset = CGPointMake(0, [self.tableView contentSize].height - self.tableView.frame.size.height);
[self.tableView setContentOffset:bottomOffset animated:NO];
However, this is only partially successful. First, it doesn't work if I put it in viewDidLoad or viewWillAppear, only in viewDidAppear, which means that the user sees the tableview with the cells at the top first, then they move to the bottom. Second, if they scroll the table view, when they let go it automatically "snaps" back up to the top.
Does anyone know how to change this behaviour?
One option to consider is to resize the UITableView itself based on how many rows you will be displaying. Presuming that your UITableViewDelegate implements heightForRowAtIndexPath one can then set the height of the UITableView in a viewWillAppear method by multiplying the number of rows by the height of each row.
Something like this:
CGRect frame = [myTableView frame];
frame.size.height = [[myTableView dataSource] tableView: myTableView numberOfRowsInSection: 0] *
[[myTableView delegate] tableView: myTableView heightForRowAtIndexPath: [NSIndexPath indexPathForRow: 0 inSection: 0]];
[myTableView setFrame: frame];
This example assumes your table has one section and each row is the same height. Computing the size would have to get a little more complicated if multiple sections are involved or if different rows might be different heights.
Regardless of how the height is calculated the essence of the idea though is to just make the table itself shorter, no taller than the one or two rows that it is displaying, rather than trying to force it into behaving differently.