I need to write an excel-like grid that can have a lot of cells (400x400). All columns have the same width and all rows the same height. Each cell can contain text or be empty and each cell can have a column and/or row span. I suppose this will never work with the Grid panel and I suppose I will need UI virtualization in both column and row direction.
So my first try was to create a virtualizing grid by deriving from VirtualizingPanel and implement IScrollInfo. This could have "easily" be the solution except that I ran into a problem:
To provide IScrollInfo with the relevant information about scroll size and position and to be able to detemine wich items need to be created (realized) next using the ItemsContainerGenerator, I need to know the column index, row indeox and columnspan for each child item (cell). The only way I can think of to do this is using attach properties. The problem is: I can only read the values of attached properties if the ItemContainer that has them is already realized. So I am in a catch 22 here. To know what to realize I need to realize all items. To provide the data for IScrollInfo I need to realize all items.
So it seems that I am at a dead end with this approach.
Do you have any idea how I could implement a control like this or know how I could reslove the above problem?
It strikes me that you may not need to instanciate the UI elements themselves- you can very easily have a collection of DependencyObject-derived viewmodels, each of which has the WidthProperty and HeightProperty set (and possibly bound to the equivalent Width and Height properties of the visible cell UI element, once those are created).
Storing 160,000 (400x400) class instances shouldn't be a problem, especially if you are able to index into the set using row and column.
Related
I am making WPF application.I have a data grid and all columns have set their width to "Auto".When i start scrolling through the table some of the columns start expanding.My question is: Can I set the column width to fit the longest data in column at the beginning (without expanding columns when i scroll)?
the column width for wpf expanding when the shown data need more space when it set to Auto then this work will be done automatically.
Well this is due to the virtualization of the DataGrid. Only the items, which are visible are rendered and the controls are reused in case of scrolling (if you are activating it). And so the width will not be correct, since the longest element is not rendered yet. A list control performs very well, although you might bind many items to it.
I think you have 2 options
Turning off the virtualization, which might be a proper solution, if you don't have many items to show. I've to admit, I didn't try it, so no warranty. You can turn it off via <DataGrid VirtualizingStackPanel.IsVirtualizing="False"/>. For more information on the VirtualizationStackPanel pls have a look here.
Another solution may be TextTrimming. TextBlocks can show Ellipses if the text is too long. Therefor you will have to assign a custom datatemplate to the column put the following as content e.g. <TextBlock Text="{Binding}" TextTrimming="WordEllipsis"/>. Please note, that you will also have to provide a customer CellEditingTemplate, if the user shall be able to edit the values. For more information about TextTrimming please have a look here. To get an idea how the whole DataTemplate thing regarding DataGrids will work, you can have a look here.
I was wondering what the best way was to create an empty datagrid.
For example after you have hit new in excel, You have a grid with empty rows and columns.
I am using c# with WPF and .net 4.0.
Thank you.
As the comments have suggested, a datagrid is not a spreadsheet, but a method to display / edit existing data. That said if you want something similar, feel free to populate a collection with default / 'empty' objects and bind that to your grid. It just means that after working with the data, you will have to define a method to capture only the edited rows. This still means that the column-bound properties of your class need to be known ahead of time.
A DataGrid is used to display a collection. If you want to create an individual row DataGrid is not really the right tool. You could but a single empty row in the DataGrid using a collection of only on row. There is a lot of guidance on Master Detail on MSDN. If you don't know how many columns at design time you could used a DataGrid to turn the row vertical with column 1 as name and column as value so now you have one record but with a collection of fields.
I've written a custom panel which displays its children docked either vertically or horizontally, separated by moving splitters in between. Since the Grid panel offers much of this functionality out-of-the-box, I just inherited from it.
To create the layout, upon Loaded is fired I do the following:
1) Read how many children it has and create the appropiate number of rows/colums.
2) Position every existing children in the corresponding row/colum.
3) Create, position and add a GridSplitter for every child.
This approach looks and works fine, but it opens the door to a lot of problems:
Since it's added a GridSplitter for each child, there are twice the number of expected children. If someone added 3 elements to it, Children.Count would return 6.
User could insert/remove things at the wrong place.
It just throws an exception when this Grid is used as the ItemsPanel for an ItemsControl, since in this case WPF (not Silverlight) does not allow direct children manipulation.
These 3 cases are the ones I've already tested, but I'm pretty sure a lot more would arise depending on what the user does with it.
As it turns out, this class must be regarded as 'implementation details', so the real question is, what control should I put in front of the user?
It sounds like it should be a Panel, but I can't control the Children property since it's not virtual, and there's also the ItemsControl which I think could be a good candidate, but I really don't know.
I'd much appreciate any kind of advice or some directions to do this the right way.
Thanks in advance.
You see using just grid you leave yourself with an imperative way of adding items only. As in
myCustomGrid1.AddMyItem(***), Grids simply don't have ItemsSource property. ItemsControls do - so if you need support for declarative items sources i.e. myControl.ItemsSource = {Binding ...} you're going to derive your control from ItemsControl. This is not a two liner - making your ItemsPanel Children writable is a big challange - there's no simple way of doing that.
This is all about a small thing overlooked during the Grid's design - splitters shouldn't have been added to Children collection, as Children are visulaizations of your BOs while spliiters are just formatting elements.
Here's what I would do.
Forget about ItemsSource & items altogether - it's aint worht the hassle. The only way to add/remove items to your control will be AddResiazableItem/RemoveResizbleItem. Calls will add items and splitter (for the middle items), extend the number of rows/cols of your grid depeneding on its orientation, set Grid.Row/Grid.Column attached properties for your visual children. You can keep your actual objects internally to support Orientation change.
If at any stage you'll want to bind your control to IEnumerable source - just create an attached behavior, which will iterate through the items and call AddResiazableItem within a loop.
Cheers.
P.S. To moderators - the editor seems to get broken, lads. I cant see the second item.
P.S.S. Got it fixed after a few tries.
I have always been using a Syncfusion virtual grid which works on the basis of an override on that grid that is fired for each cell that is visible! It provides me with information on the row and column and some cell object that lets me set the value of that cell, its formatting, colours etc.
This allowed for very fast scrolling on very large datasets, since I simply have to 'read out' the value like dataSet.Tables[0].Rows[1000000]["LastName"].ToString()
Is there anything similar exposed by the WPF DataGrid?
EDIT
I need to make myself clearer - I know about virtualization and that it switches itself off when you do grouping etc. Having run a test with grouping enabled over a dataset of 20,000
rows made my grid choke on itself.
Therefore my previous question stands on its own!
Is there any way the grid allows me to fill in the text and do some formatting through some override or callback?
Thanks
The DataGrid uses virtualization by default. This works by either creating and deleting cells on the fly or by recycling the visible cells and repopulating them with the current row's data. This can be turned off as well as tweaked by playing with the 'VirtualizingStackPanel.VirtualizationMode' property and is forced off in many situations (grouping is a good example). This virtualization can be a godsend and a curse. If you have a simple set of requirements, then it makes it dead easy to get good performance. If on the other hand you are doing complex runtime binding, including triggers and custom columns, then it becomes a bit of a nightmare.
a couple of important reads:
http://msdn.microsoft.com/en-us/library/cc716879.aspx
http://msdn.microsoft.com/en-us/library/system.windows.controls.virtualizingstackpanel.aspx
I have a list of string array as input. The array dimension are static for all the list but I can't know the array size until the list is retrieved.
I need to bind the list in a datagrid in Silverlight.
I tried to create columns at runtime, binding each column to a particular array position but cannot find a way.
Have you any idea how to do it?
I could eventually "convert" my list of array in anything else that could be binded in a datagrid?
The idea is to have a sort of 2d Matrix showed inside the datagrid in Silverlight (I think that the problem is similar).
List
column_1 column_2 column_3 .. column_m
string[1,1] string[1,2] string[1,3] .. string[1,m]
string[2,1] string[2,2] string[2,3] .. string[2,m]
string[3,1] string[3,2] string[3,3] .. string[3,m]
....
string[n,1] string[n,2] string[n,3] .. string[n,m]
n is list lenght, m is list column max number.
Any idea is appreciated
I've found two solution to the problem that use the schema in the Denis's answer:
the first one is to use reflection to generate a class at runtime for the binding as suggested in this article (thanks to Vladimir Bodurov). I've tested this solution and I'll try to use it on my project. The only problem right now is that for large collection, the performance are poor. But I hope that someone will fix it in next relese (Silverlight 3 seems to not have fixed this problem, yet)
the second solution will be using some dynamic language for generate data. I don't know if this could be faster or not (probably not) but eventually could help. I will try in the future and use ironpython or ruby to generate classes that will be binded in datagrid.
If anyone have tryed using the second solution or any performance related information about creating classes at runtime, it will be appreciated.
Giorgio
Unfortunately that's not gonna be easy.
Do you have any valid constraints, like the maximum number of columns that is allowed or anything like that?
If you do (let's say you have N column maximum), you might be able to do something by
Having a class that exposes N
properties (named Col1...ColN for
example) that map the content
of the array for one line at column
X
Generating a list of that class,
one instance for each line
Generating the correct number of
column on the fly, binding each
column to property ColX
Binding your DataGrid to that list
That's kind of ugly, but it would work.
If you do not have to rely on the DataGrid, there is a possibility using a UniformGrid. A UniformGrid is a panel that layouts its children in a regular grid (every item has the same width, every item has the same height). You can indicate the number of columns at runtime, and the panel will fit children one after the other up to the number of columns and then continue on another line.
You could bind an ItemsControl to your array, indicating it should use a UniformGrid as its layout panel and indicating a suitable ItemTemplate to render each string.
The second option is much easier, but you will not have the capabilities of the DataGrid like sorting, moving columns, row selection, edition events per row etc.