I want to look up a label at runtime, is this the correct way to do it?
Control[] control;
Label label;
control = this.Controls.Find(labelToChange, false);
label = (Label)control[0];
I couldn't find a method that returns a single control, so I had to store it a collection and then retrieve the first one. It will always find a single item.
This is the correct method to use.
The MSDN documentation doesn't indicate why it returns a collection, but if you have the a control that encapsulates several sub controls and instantiate that several times you will end up with a collection of labels.
So:
If you can guarantee that there will only ever be one control visible at any one time your code is OK.
If there could be more than one, then you need to loop over all the controls that are returned and either perform the same action on each or add some more code to work out which one you really want.
Basic idea in linq:
Label label;
var c = from x in Controls.Find("labelToChange", false)
where x.GetType() == typeof(Label)
select x;
label = (Label)c.FirstOrDefault();
Related
Documentation says it must be done inside someDataGridView.CellFormatting event, but how can you pass the needed color information into it and force CellFormatting to be triggered when needed ?
someDataGridViewCell.Value is working fine for changing cell text from a System.Windows.Forms.Timer Tick event, but I can't seem to change the coloring at the same time.
In my case, all the columns are built and changed dynamically from user menus, and there can be dozens of them.
This is VS2015.
Update:
My issue was I used Color.FromName() which returns Empty (transparent) for misspelled names -- very very bad for grid background colors. (I required coloring in data streams I was using so name seemed handy.)
CellFormatting event used in most examples assumes you can derive the color information from the visible cell contents which is too limiting.
Using the CellFormatting event is recommended if you are changing colors on the datagridview on the Load event of the Form. Once the form has been Shown you can modify the cells in any method.
How you would do it would depend on how you iterate through the view and what you're trying to accomplish. Since you didn't specify VB or C# I'll put both.
Single Cell:
VB:
dgv.Rows(index).Cells(index).Style.BackColor = Color.PickAColor
C#:
dgv.Rows[index].Cells[index].Style.BackColor = Color.PickAColor;
Entire Row:
VB:
dgv.Rows(index).DefaultCellStyle.BackColor = Color.PickAColor
C#:
dgv.Rows[index].DefaultCellStyle.BackColor = Color.PickAColor;
Entire row while through the rows:
VB:
For Each row As DataGridViewRow in dgv.Rows
row.DefaultCellStyle.BackColor = Color.PickAColor
Next
C#:
foreach(DataGridViewRow row in dgv.Rows)
{
row.DefaultCellStyle.BackColor = Color.PickAColor;
}
Essentially if you're styling a single cell use the Cell.Style.BackColor and if you want to do the entire row then use the Row.DefaultCellStyle.BackColor
I'm trying to wrap my head around array lists in vb.net. I am self teaching via the internet but can't seem to figure it all out. Some points i'm having trouble connecting the dots to:
How do i make the array list universal so it's not stuck in a subroutine and I can allow any sub to access the list.
Allowing the list to be added to or removed from from another control on the form.
Saving this array list so the program will populate the list box with it on startup.
Here is an image of the basic concept for the visual:
https://imgur.com/lBbopD8
Up to question 3, using a List(Of T) was the way to go. It may still be but certainly not completely and maybe not at all. Before the advent of the List(Of T), Microsoft recognised that storing Strings in a collection was the most common requirement so, to provide type-safety in that case, they provided the StringCollection class. You say that you want to persist your list of values between sessions so that probably means using My.Settings and it is actually possible to create a setting of type StringCollection.
I would suggest that you open the Settings page of the project properties and add a setting of type StringCollection. Once added, that list will be automatically loaded at startup and saved at shutdown, with no code required from you. You can access it anywhere in the app via My.Settings and you can call Add and Remove or index it or loop over it in exactly the same way as you would an ArrayList or List(Of String).
There is one small gotcha with a StringCollection in settings though. It will actually be Nothing by default. The trick to avoiding that is to edit its Value on the Settings page to add an item, commit that, then edit it again to remove the item. You'll see that, instead of the Value field being empty, it will then contain a snippet of XML. It's that that creates the StringCollection object in the settings file.
As I said, if you want to persist this list between sessions then I strongly recommend using settings this way. Just note that, in order to edit settings, they have to be User-scoped rather than Application-scoped. What that means is that each separate Windows user will have their own copy of the setting and thus their own value. If you only log into Windows with one account then it's of no consequence. If multiple Windows users use the app then it may be considered beneficial in most cases but may be a problem if you want universal settings that can be edited. If it's a problem, you will need to handle persistence yourself but be aware that a standard Windows user (as opposed to an admin) won't have access to write data everywhere, which is exactly why User-scoped settings work the way they do.
Also, while you must use a StringCollection for persistence in settings, you may or may not want to use the same collection in the rest of your code. You might access the collection directly all the time or you may choose to copy the collection to a List(Of String) at startup and then copy the data back at shutdown. Unless you want to avoid committing items until shutdown, I wouldn't bother with the extra collection.
So an important thing to know is that you can directly populate and edit the listbox without having an additional ArrayList. You would use the example code below as follows:
'addTb is the text box you had in the image; this will run on button press event
ListBox1.Items.Add(addTB.Text)
If you are looking to dump ArrayList data into the list box use something like this:
'creates new arraylist and adds items to it
Dim listStuff As ArrayList = New ArrayList
listStuff.Add("Hi")
listStuff.Add(2)
'makes listStuff the datasource for your list box
ListBox1.DataSource = listStuff
Finally, if you are wanting to loop through ArrayList items use something like this:
'remember to do count - 1 or you will receive error since index will be out of range
For i = 0 To listStuff.Count - 1
If listStuff.Item(i) = "" Then
'do stuff here
End If
Next
Hopefully that helps. Let me know if I need to be more clear since this is my first stack overflow answer :)
You are using a ListBox control to visualize a collection of presumably String values from a TextBox control. The ListBox exposes the visualized collection via the Items property.
How do i make the array list universal so it's not stuck in a subroutine and I can allow any sub to access the list.
Because the ListBox control resides on the Form, you can access the Items property through any access level in your Form's code.
Allowing the list to be added to or removed from from another control on the form.
From the Items property, you can use the Add method to add a single value, the AddRange method to add multiple values via an array or another ListBox collection, the Insert method to insert a value at a given index, the Remove method a specific item, and the RemoveAt method to remove an item at a given index.
So in your case, since you're presumably adding the value from the Text property of the TextBox to the ListBox, it is as simple as:
ListBox1.Items.Add(TextBox1.Text)
Saving this array list so the program will populate the list box with
it on startup.
You have a few options, but generally the idea is to is write each value in the Items property to its respective line at a given file when the application closes and then load each value back by reading each line from the same file. Another option is to use My.Settings, though I think with your level of expertise, it would probably be better to stick with the read/write to a file option so you don't have to worry about some pitfalls associated with this option. Here would be a quick example of reading/writing the items to a file:
'Write the items to the file
Dim items(ListBox1.Items.Count - 1) As String
ListBox1.Items.CopyTo(items, 0)
IO.File.WriteAllLines("file.txt", items)
'Read the items to the file
ListBox1.Items.AddRange(IO.File.ReadAllLines("file.txt"))
I am quite new to WPF, coming from the Delphi world. I solved the problem below (albeit painfully) in the Delphi world, and hope there is a more elegant solution in the WPF world.
I need to read in an XML file containing a menu "tree", which has the window names in it as well as the menu prompts, and then be able to "show" a window based on having its name.
For example, a segment of the menu, with two choices, might have XML like this:
<MenuLeaf>
<Header>Product information</Header>
<MenuLine>
<Prompt>Product Master File</Prompt>
<WindowName>Products.xaml</WindowName>
</MenuLine>
<MenuLine>
<Prompt>Inventory Data</Prompt>
<WindowName>Inventory.xaml</WindowName>
</MenuLine>
</MenuLeaf>
So when the user makes the "Inventory Data" choice, I will know that I want to do a "show" of the window Inventory.xaml ..... but I only have the literal string "Inventory.xaml".
I will have hundreds of these forms, and the XML file can vary from time to time - so it's not effective for me to have the standard code of
Dim window as New Inventory
window.Show
for each of the several hundred windows.
What I need is something that does
Dim window as New {go out and find the Inventory file with name Inventory.xaml}
window.Show
I have searched endlessly for this with no luck.
I think the path to solution is to use Reflection, which will allow you to dynamically find/invoke your classes. Say your Namespace is MyNs, then you must have a 'Products' Class within it that correspond to the 'Products.xaml' file. To find it, use MyFoundType = MyNs.GetType("Products")
Then get default (or other if you like) constructor for this type : MyFoundType.GetConstructor(). Then invoke the constructor (with arguments if needed) --> you now have your window as an Object.
Cast it to a window and call its Show method, and you're done.
http://msdn.microsoft.com/en-us/library/y0cd10tb.aspx
http://msdn.microsoft.com/en-us/library/h93ya84h.aspx
http://msdn.microsoft.com/en-us/library/6ycw1y17.aspx
You need to use the XamlReader object, which parses XAML at run-time and creates the object.
var rdr = XmlReader.Create(File.Open("Inventory.xaml"));
var window = XamlReader.Load(rdr) as Window;
window.Show();
The XamlReader.Load will return whatever the actual top-level element in the XAML specifies; if it's a Window you can just .Show it. If it's something else, you'll need a container to place it in. For example, you might have a Window with a Border element in it and do:
var control = XamlReader.Load(rdr) as UserControl;
var window = new MyHostWindow();
window.ContentBorder.Child = control;
If you don't actually know the type of element in your XAML you can usually use FrameworkElement, which is the base class for all the visual elements, though you won't get Window-specific behavior from that.
I'm trying to implement the following: I have an Items Manager, that has an Item class inside. Item class can store two possible visual representations of it - BitmapImage(bitmap) and UserControl(vector).
Then later, in the game, I need to share the same image or vector control between all possible places it takes place. For example, consider 10 trees on the map, and all point to the same vector control. Or in some cases this can be bitmap image source.
So, the problem is that BitmapImage source can be easily shared in the application by multiple UIElements. However, when I try to share vector control, it fails, and says Child Element is already a Child element of another control. I want to know how to organize this in the best way. For example replace UserControl with other type of control, or storage, however I need to be sure it supports Storyboard animations inside.
The code looks like this:
if (bi.item.BitmapSource != null)
{
Image previewImage = new Image();
previewImage.Source = bi.item.BitmapSource;
itemPane.ItemPreviewCanvas.Children.Add(previewImage);
} else
if (bi.item.VectorSource != null)
{
UserControl previewControl = bi.item.VectorSource;
itemPane.ItemPreviewCanvas.Children.Add(previewControl);
}
Or it is not possible to share same control in different places, then what is the best way to make a copy, or the best way to store vector data.
Thanks in advance
So, I found the problem. It is possible to attach the same UserControl to different controls.
However, when on update I was deleting control, and then filling up it again with a new pointer, that sometimes was the same as before deleting, somehow it was still in memory. And so it was like 2 same user control attached to the same parent.
I added a line of code that was cleaning all children in control, before updating it with new vector UserControl, and now works like a charm.
I have set up a dialog with several tabs. One of these contains twenty combo boxes, each with over 100 items, added like this :
foreach (var x in collection)
{
string text = FormatItem (x);
combo.Items.Add (text);
}
so there is nothing fancy at all with the items. They are plain strings and the combo boxes get filled when the dialog is created. This happens almost instantenously.
However, when the user clicks on the tab containing all these combo boxes for the very first time, the GUI freezes for several seconds (and I am running on a really beefy machine).
I loaded the symbols for System.Windows.Forms and tried to break into the debugger while the program is stuck. What I have discovered is a stack trace with the following calls:
System.Windows.Forms.Control.CreateHandle()
System.Windows.Forms.ComboBox.CreateHandle()
System.Windows.Forms.Control.CreateControl(...) x 3
System.Windows.Forms.Control.SetVisibleCore(true)
System.Windows.Forms.TabPage.Visible.set(true)
which results in plenty of native transitions, WndProc calls, etc. I suppose this happens for every single item in every combo box. Phew.
Obviously, I cannot optimize WinForms. But maybe I can take some actions in order to avoid all this hell getting lose on my poor GUI? Any ideas?
Nota bene:
I've no event handlers attached on the combo boxes which could be called when the controls get created for real.
If I try to access the Handle property of the combo boxes just after having created and populated the form, I pay the penalty at that moment, rather than when the tab becomes visible for the first time. But having to wait several seconds when creating the form is not acceptable either. I really want to get rid of the long set up time.
The idea of applying BeginUpdate and EndUpdate does not apply here: these should be used to prevent the control from repainting when its items list gets filled. But in my case, the problem happens well after the control has been set up.
What you're saying is not consistent with anything I ever observed... :s
But have you tried using .BeginUpdate / .EndUpdate ?
Another thing you coud try is not populate the boxes until needed. Delay it until the box gets focus for example... (If you trap the dropdown event some user might be annoyed that the up/down arrow keys won't work.)
Everything I tried failed up to now to speed up the first display of the tab containing all the combo boxes. Data binding didn't help either.
I finally decided to fix the issue by doing a trick, similar to what danbystrom proposed, i.e. only populate the Items collection when the focus first arrives on a combo. This still produces a noticeable delay, the time all items get created (within a BeginUpdate and EndUpdate pair of method calls), but it is tolerable (approx. 200ms versus several seconds in my original scenario).
Instead of iteration your collections, would't setting the ComboBox.DataSource be a viable, and much faster alternative?
comboBox1.DataSource = myCollection1;
comboBox2.DataSource = myCollection2;
comboBox3.DataSource = myCollection3;
// and so on...
Here is a more complete example:
public class Entity
{
public string Title { get; set; }
public override string ToString()
{
return Title;
}
}
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
List<Entity> list = new List<Entity>
{
new Entity {Title = "Item1"},
new Entity {Title = "Item2"},
new Entity {Title = "Item3"}
};
comboBox1.DataSource = list;
}
I've just been coming up against this same problem, where populating a combobox with around 4000k items was unacceptably slow.
I was filling the combo in the OnLoad event handler of a form, however, when I shifted this code to constructor, after InitializeComponent(), there was no delay at all.
I guess doing this operation in the OnLoad was causing a redraw of the combo to fire, hence the delay? Anyway, just thought I'd add this in case it's of use to anyone else in this situation.
Lots of controls on a form can be a problem. I once had a form that dynamically created between 50-100 textbox controls. It was slow to load.
We solved that problem by using a datagrid instead. It's a control that is optimized for lots of data. I don't know what your exact requirements are, but it might work.