We have a TableView showing a large amount of data. It is a typical use case to select the whole table for some further processing.
This can be done via Ctrl A keybinding. Since the table content is quite large, this selection can take a second or two, which tends to irritate users.
How can I show a Wait Cursor between pressing the keys and the time the selection is actually showing up?
Displayed data might be lazily fetched, depending on the RAM available, so this might be a source of the delay. But I am not sure about this, it might as well be just the "selection" itself.
I am imagining to catch the select-all-event, call scene.setCursor(WAIT), selectionModel.selectAll() and scene.setCursor(DEFAULT) again. But I don't know how to do that nor if that would be even the right approach.
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tl;dr
In a program that calls a function onEnterFrame on each frame, how do you store and mutate state? For instance if you are making a level editor or a painting program where keeping track of state and making small incremental changes are tempting / enticing / inviting. What is the most performany way to handle such a thing with minimal global state mutations?
long version:
In a interactive program that accepts input from the user, like mouse clicks and key strokes, we may need to keep track of the state of the data model. For instance:
Are some elements selected?
Is the mouse cursor hovering over an element, which one?
How long is the mouse button held down? Is this a click or a drag?
We also, sometimes need make small changes to a large model:
In a level editor, we may need to add one wall to an existing large set of prefabs. You don't want to recreate the set, no?
Read Prof Frisby's mostly-adequate-guide so far, there are many functional solutions to issues that deal with extracting a piece of data from some source of input, performing computation on that data and passing the result to some output.
Sometimes an app let's the user interact and perform a sequence of mutations on data. For instance, what if a program let's the user draw (like Paint) on a canvas and we need to store the state of the painting as well as the actions that led to that state (for undo and logging/debugging purposes)?
What state is acceptable to store and what should we absolutely avoid?
Currently my conclusions is that we should never store state that we only need temporarily, we should pass it to the function that needs it directly.
But what if there are several functions that need a specific computation? Like the case in which we check if the mouse's cursor is hovering over a specific area, why would we want to recompute that?
Are there ways to further minimize mutations of global state?
Storing state isn't the problem. It is mutating global state that is the problem. There are solutions to handling this. One that comes to mind is the State Monad. However, I am not sure this is ideal for undoing operations. But it is a place to start.
If you just want to look at the problem as an initial state and a set of operations then you can think of the operations as a List that can be traversed (with the head being the latest operation). Undoing a set of n operations could be accomplished by traversing the first n elements of the list and cons-ing the inverse of these operations to the list.
That way you don't modify global state at all.
I have custom data that I need to display in a QTreeView. I have derived my model from QAbstractTableModel, and made my own implementations of rowCount(), columnCount(), data(), and headerData(). The model has a local QList> to support it, and the data() function is defined to read the values out of that list of lists directly corresponding to the row and column received in the QModelIndex parameter. There are two issues I'm running into.
The first is that the load of a very large file is quite slow, which is understandable. The second is that the scroll action is painfully slow, which I am not really understanding. Turns out that if I pull the scroll handle down, the GUI hangs for about 20 seconds, and then pops back. If I pull the handle a greater distance down, the hang time increases accordingly. If I pull the handle all the way to the bottom of the scroll bar, after waiting for the application to become responsive again, I can pull the handle up and down and get much better response.
It seems to me that QTreeView is only asking for a small chunk of the available data, but when I have pulled the scroll handle all the way to the bottom of the scroll bar, once the application becomes responsive again, it has by that point read all the data.
Is there a way to program for a much more responsive experience with scrolling for large data? I don't mind a longer wait up front, so just something like forcing the view to read all data from the model up front would work.
I have also thought that I could go back to just deriving from QAbstractItemView and controlling how it requests and stores data, only allowing for storing the viewed data, plus a buffer of entries before and after the viewed data. That of course would mean I'd have to control the scroll bar, since the handle sizing would indicate a small amount of data, and I would like it to look to the user as it should for the size of data they are dealing with. Not really wanting to go there if I don't have to.
Two things:
Re-implement fetchMore() and canFetchMore() in your model. See this implementation example. Basically, the two functions allow lazy initialization of your data and should stop ui freezes.
Replace your usage of reset() and dataChanged() to use the insert and remove functionality. Right now, you are forcing the view to recalc which of 100,000 items to show.
use
treeview view;
view.setUniformRowHeights(true);
Then view do n't hangs.
I'm working on a Python+Gtk3 application with a fancy-looking GtkTreeView:
This is great for sighted users, but here's what Orca (the screen reader) says for a row in that tree view:
"Image, Devhelp, Collapsed, 9.2 MB"
A few problems, of course. First, it doesn't mention the checkbox for each row because I'm packing three cell renderers into a column. The three are available, but for some reason Orca doesn't mention the checkbox when it's buried that deep. Meanwhile, the image it mentions is the one on the far left, which is usually empty but sometimes a "restart required" indicator. Naturally, a blind user, much like a sighted user, couldn't care less that it is an image.
What I would like to do is to poke at the accessibility objects that describe this table in order to make them a little more helpful. Using Accerciser, I can see that these exist, but they all seem to be implemented with private, undocumented classes (like GtkTreeViewAccessible), and they don't look terribly extensible, but I'm hoping I'm wrong. Knowing that the treeview's accessible object is an AtkTable at some level, I did the following to set an accessible description for the image cell in the Backup row:
access = self.treeview_update.get_accessible()
cell_access = access.ref_at(0,0)
cell_access.set_image_description("Requires system restart")
(Orca still says "Image" after speaking the description, but I'll assume it knows what it's doing).
However, that code isn't very nice. When I call access.ref_at, I'm making particular assumptions about how GTK is mapping cell positions to rows and columns in the ATK object. I'm also limited to calling that when I first populate the tree, and I'm not sure if that is particularly sane.
So there's my problem: I would like to add accessible descriptions for my tree view cells in a nice way that won't break unexpectedly. How can I do that?
I am currently using powerbuilder 6.5
In my application, i want to make a code where any change in one window should reflet another window.Two windows are using the same table. if we channge in one window it is not reflecting in another window if the other window is opened earlier. what cani do?
It might help to know a little more about what you are trying to accomplish. Are both windows open at the same time on a single user's screen? Or is one window available to one user and the second being viewed by a separate user waiting to see the updates?
By themselves, the datawindows won't retrieve automatically on updates to the underlying table. In fact, if you have configured the datawindows properly, the update rules should provide some concurrency protection and will not let the second dw update the same table after the first updates. DataWindow2 will sense there's been a change and will try to prevent clobbering the DataWindow1's changes. But again, this may not be an issue if in your context the second window is read-only.
You could have the first window finish its update then check for the existence of the second window and have it retrieve. Even better, use a non-visual business object as an intermediate handler (and also keep nasty cross-window communication code out of the GUI). When the first window's update is successful have it tell the business object it's done, and the object can then tell the second window to retrieve. But there would need to be more done if your second window is updateable.
Use the datawindow ShareData method to share the content of the two datawindows (you do mean datawindow when you say table, right?).
BTW, I feel for you, having to use that PB 6.5 dinosaur. OTOH, we've just migrated from PB 10 to shiny new PB 11.5, and it has the worst IDE I have ever used. As a programmer, I'm embarrassed to see such am awful software. Sybase should be ashamed of themselves, releasing such a lousy product.
# eran
No i meant table only.
Two windows are using different datawindow and for these datawindow it is using same table.
So if we change in one window it wont reflect that change in other window if it opened one.
I have a web page that loads some data via a SQL query into a datagrid. I was asked to add a new column. During testing I discovered that pulling this extra column of data from the database slows the query down substantially. What used to be a sub-second query now takes about 3-4 seconds. I've checked the database and all the appropriate indices are in place, and a database change wouldn't be practical here.
Anyway the slow down in the page loading could really impact productivity.
If it's possible and practical, this is what I would like to do. I'd like to render the datagrid as before with the original query, but leave and extra column blank. Then after the page is rendered use Ajax to go back to the server and get the data for the remaining column and populate it. That way, those users who don't need the extra column to do their work, don't have to wait so long for the page to render, but those who need it can just wait a few seconds and the data will be there.
The problem is, I don't have the faintest idea how to put this together. Any suggestions?
Give the user an option to display the extra column or not. Then have two queries that can bind to the GridView, one that returns the extra column and one that doesn't. Then it is up to the user to decide which "view" they want. So that they do not have to decide every time they open or refresh the page, you persist their selection.