Develop Reference

How to retrieve selected values for selected items in a ListBox?

I'm populating a ListBox in a WinForms application, this way:
listBoxUsers.DataSource = ctx.Users.ToList();
listBoxUsers.DisplayMember = "Name";
listBoxUsers.ValueMember = "Id";
how to retrieve the selected Ids when I'm setting the SelectionMode to MultiSimple
I want to do a foreach loop on them, like this:
foreach(var itemId in listBoxUsers.SelectedValues)//unfortunately not exist
{
int id = int.Parse(itemId);
// . . .
}

Since you know the type of items, you can use such code:
var selectedValues = listBox1.SelectedItems.Cast<User>().Select(x=>x.Id).ToList();
Side Note: The ListBox control lacks a GetItemValue method. A method which should work like GetItemText, but for getting values. In the linked post I shared an extension method to get the value from an item. Using that extension method you can get selected values independent from type of items:
var selectedValues = listBox1.SelectedItems.Cast<object>()
.Select(x => listBox1.GetItemValue(x)).ToList();
If for some reason you are interested to have a text representation for selected values:
var txt = string.Join(",", selectedValues);

Have you tried with the SelectedItems property?
foreach (var item in listBoxUsers.SelectedItems)
{
}

try this:
foreach (DataRowView item in listBoxUsers.SelectedItems)
{
int id=int.parse(item[0].ToString());
}

How to insert first item in combo box with text "SELECT" with default value 0 in C# windows application

I am using C# windows application. My code is as below
var categoryList = _objCategoryManager.GetAll();
cmbCategory.DisplayMember = "Name";
cmbCategory.ValueMember = "Id";
cmbCategory.DataSource = categoryList;
Here categoryList is of type IEnumerable. I want to insert item in ComboBox at 0 index i.e."--SELECT--"

You cannot insert item to your ComboBox after data binding. Instead insert the item in a copy of your data source before, then do the binding.
If categoryList is IEnumerable<T> and not a List<T> then you should copy it to a List<T> so that you can add your default value at the first index:
var categoryList = _objCategoryManager.GetAll().ToList();
categoryList.Insert(0, new Category {Id = -1, Name = "--SELECT--"});

Simply insert it into your list, so something like
var categoryList = _objCategoryManager.GetAll().ToList();
cmbCategory.DisplayMember = "Name";
cmbCategory.ValueMember = "Id";
categoryList.Insert(0, new Category() { Name = "--SELECT--"} );
cmbCategory.DataSource = categoryList;

categoryList.ToList().Find(o => o.ID == Convert.ToInt32(0)).Name = "--SELECT--";
Using LINQ, you can find the object you want to change (after binding) and modify that item.
Otherwise if you are adding an object into the list:
categoryList.ToList().Add(obj); // This should show the new item in the combo box
Ultimately your .GetAll() method should have returned the first one to be "--SELECT--" instead of trying to modify it afterwards.

Store elements from a ListView into a List

Since I haven't found anything that helped, I ask my question here:
I have a ListView where I select a whole row by click. Now I want to store these selected items into a List but don't know how this should work exactly.
List<String> itemSelected = new List<String>();
foreach (var selectedRow in listView1.SelectedItems)
{
itemSelected.Add(selectedRow);
}
That doesn't work because I need an index (selectedRow[?]) or something like that. How can I store the values of the first column when clicked the row?
EDIT: The problem is that the ListViewItems have the type "object"
The ListView gets populated this way:
using (SqlConnection connection = new SqlConnection(connectionQuery))
{
foreach (DataGridViewRow row in dataGridView1.SelectedRows)
{
col1 = row.Cells[col1.Text].Value.ToString();
col2 = row.Cells[col2.Text].Value.ToString();
col1Cells.Add(col1);
col2Cells.Add(col2);
}
}

You can do something like:
ListViewItem listViewItem = this.listView1.SelectedItems.Cast<ListViewItem>().FirstOrDefault();
if (listViewItem != null)
{
string firstColumn = listViewItem.Text;
string secondColumn = listViewItem.SubItems[0].Text;
// and so on with the SubItems
}
If you have more selected items and only need the values of the first columns you can use:
List<string> values = listView1.SelectedItems.Cast<ListViewItem>().Select(listViewItem => listViewItem.Text).ToList();

It's common to bind a ListView to the List of non-trivial types.
Then you can handle SelectedItemChanged or something like that. You receive the whole object (in type object) which you can cast to your custom type and retrieve any properties you want

How do I bind a DataGridViewComboBoxColumn to a property/method of an object that returns a list?

I have a custom object with several properties, one of which returns a list. This is the code for the object:
public class SearchResult
{
private int eventId;
private String eventTitle;
private int startDate;
private List<String> tags;
// Properties
public int EventId { get { return this.eventId; } }
public String EventTitle { get { return this.eventTitle; } }
public int StartDate { get { return this.startDate; } }
public List<String> Tags { get { return this.tags; } }
public SearchResult(int eventId, String eventTitle, int startDate, List<String> tags)
{
// Constructor code
}
public List<String> GetTags()
{
return this.tags;
}
}
I also have a DataGridViewComboBoxColumn that I want to bind to the Tags property. Basically, each SearchResult object will be displayed in its own row, and I want the List<String> in the Tags property of each object to be displayed in a ComboBox cell in that row. This is the code I have so far for my DataGridView:
BindingList<SearchResult> results = new BindingList<SearchResult>();
results.Add(new SearchResult(1, "This is a title", 2012, new List<String> { "Tag1", "Tag with a long name1" }));
results.Add(new SearchResult(2, "The quick brown fox", 2012, new List<String> { "Stack", "Overflow" }));
results.Add(new SearchResult(3, "In this tutorial, you create a class that is the type for each object in the object collection. ", 2012, new List<String> { "NYSE", "FTSE" }));
results.Add(new SearchResult(4, "another long piece of title text", -999, new List<String> { "Rabbits", "Chickens" }));
MyDataGrid.AutoGenerateColumns = false;
MyDataGrid.AllowUserToAddRows = false;
MyDataGrid.AllowUserToDeleteRows = false;
MyDataGrid.AutoSizeColumnsMode = System.Windows.Forms.DataGridViewAutoSizeColumnsMode.None;
MyDataGrid.BackgroundColor = System.Drawing.SystemColors.Control;
MyDataGrid.ColumnHeadersHeightSizeMode = System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize;
MyDataGrid.RowHeadersWidthSizeMode = System.Windows.Forms.DataGridViewRowHeadersWidthSizeMode.AutoSizeToDisplayedHeaders;
MyDataGrid.AutoSizeRowsMode = System.Windows.Forms.DataGridViewAutoSizeRowsMode.DisplayedCells;
MyDataGrid.DefaultCellStyle.WrapMode = DataGridViewTriState.True;
DataGridViewTextBoxColumn eventIdColumn = new DataGridViewTextBoxColumn();
eventIdColumn.DataPropertyName = "EventId";
eventIdColumn.HeaderText = "Event ID";
eventIdColumn.ReadOnly = true;
eventIdColumn.Width = 84;
DataGridViewTextBoxColumn eventTitleColumn = new DataGridViewTextBoxColumn();
eventTitleColumn.DataPropertyName = "EventTitle";
eventTitleColumn.HeaderText = "Event Title";
eventTitleColumn.ReadOnly = true;
eventTitleColumn.Width = 368;
DataGridViewTextBoxColumn startDateColumn = new DataGridViewTextBoxColumn();
startDateColumn.DataPropertyName = "StartDate";
startDateColumn.HeaderText = "Start Date";
startDateColumn.ReadOnly = true;
startDateColumn.Width = 130;
//I think I need to insert the code for the tags column here, but I'm not sure
MyDataGrid.Columns.Add(eventIdColumn);
MyDataGrid.Columns.Add(eventTitleColumn);
MyDataGrid.Columns.Add(startDateColumn);
//MyDataGrid.Columns.Add(tagsColumn);
MyDataGrid.DataSource = results;
I derived this code from a tutorial I found online, and it works perfectly.
I've been trying to bind the Tags property of SearchResult to a DataGridViewComboBoxColumn, but I'm not sure how. I've been looking at this question, which provides this code:
column.DataPropertyName = "Foo";
column.DisplayMember = "SomeNameField";
column.ValueMember = "Bar"; // must do this, empty string causes it to be
// of type string, basically the display value
// probably a bug in .NET
column.DataSource = from foo in Foo select foo;
grid.DataSource = data;
The reason I'm having trouble is because of a few nuances of the linked question that I don't understand.
According to the documentation and the linked question, DisplayMember should be linked to the property that "contains a description of the instance", but since SearchResult objects are added dynamically and don't have any description associated with them, should I just leave it blank?
ValueMember is giving me similar problems, since I'm unsure what to put even after reading its documentation.
In the linked question, the accepted answer binds the entire datagrid at once using LINQ. Is that how I should be doing this? I'm not sure how to modify that code for my situation, but I thought it would be something along these lines.
:
tagsColumn.DataPropertyName = "Tags";
tagsColumn.DisplayMember = ""; // I'm unsure of what to put here
tagsColumn.ValueMember = ""; // Once again, I don't know what to set this to
I also presume I should have a line that sets the DataSource for the column, e.g.
tagsColumn.DataSource = <some LINQ query, perhaps?>
but I don't know because the only mostly relevant C# source I've been able to find is that question.
UPDATE:
I did find a second question that suggests code similar to this for data binding:
// reference the combobox column
DataGridViewComboBoxColumn cboBoxColumn = (DataGridViewComboBoxColumn)dataGridView1.Columns[0];
cboBoxColumn.DataSource = Choice.GetChoices();
cboBoxColumn.DisplayMember = "Name"; // the Name property in Choice class
cboBoxColumn.ValueMember = "Value"; // ditto for the Value property
Based on that, I a) added the GetTags() method to SearchResult and added this code into my DataGridView initialisation code:
DataGridViewComboBoxColumn tagsColumn = new DataGridViewComboBoxColumn();
tagsColumn.DataSource = SearchResult.GetTags(); // ERROR
tagsColumn.DisplayMember = ""; // Still not sure
tagsColumn.ValueMember = ""; // ??
However, Visual Studio gives me an error on the second line when I try to run this:
An object reference is required for the non-static field, method, or property 'SearchResult.GetTags()'
UPDATE 2:
I'm still searching around for this without success. I don't understand how with other properties (e.g. EventId) I can simply declare the data property name as EventId, and it will display in the table, but I cannot do this with ComboBox columns.
Since the objects are instantiated in a separate class and put in a list, it doesn't seem to make sense to me that I should have to loop through the entire array of objects (of which there may be several hundred) to bind the Tags property to the ComboBox column for each instance, when I don't need to loop through the list of SearchResult objects to bind other properties, e.g. EventId.
Why does this binding-properties-by-name only work for some properties and not others?

I don't quite understand why you want to use DataGridViewComboBoxColumn to display a list of elements. This column kind is designed to allow user to select one of many possibilities. It seams it is not your case because you don't have public string SelectedTag{get;set;} property to store it. As I understand your model you have many tags already selected for your SearchResult and you want to display them in grid.
As documentation states:
http://msdn.microsoft.com/en-us/library/system.windows.forms.datagridviewcomboboxcolumn.datasource
Getting or setting this [DataSource] property gets or sets the DataSource property of the object returned by the CellTemplate property. Setting this property also sets the DataSource property of every cell in the column and refreshes the column display. To override the specified value for individual cells, set the cell values after you set the column value.
DataGridViewComboBoxColumn simply does not have capability to bind items property to data source because it assumes that there is only one list of elements that is used as data source for all rows of data grid.
I also assume that you would set ReadOnly = true property for this column as you have for all other. If so it would prevent user form seeing list of tags because drop down list would never be displayed.
If you wand to display list of strings in read only mode I would suggest to flatten this list of tags to single string:
public string Tags { get { return string.Join(", ", tags); } }
and display it in text column.

For the error , i can suggest you to make an instance of the class and then call the method as its not static or you can make your method static.
Moreover As you needs the comboboxcolumn ,
DataGridViewComboBoxColumn tagsColumn = new DataGridViewComboBoxColumn();
tagsColumn.DataSource = SearchResult.GetTags(); // ERROR
tagsColumn.DisplayMember = ""; // Still not sure
tagsColumn.ValueMember = ""; // ??
Mostly we have dropdowns for objects like Country(id,name) so DisplayMember = name will be shown as text in dropdown while ValueMember = id will be used in the referencing tables in database.But this is not your case.
Here you have a list of strings to show in dropdown , so you don't need to set them.
As written here
If the DataSource property is set to a string array, then ValueMember
and DisplayMember do not need to be set because each string in the
array will be used for both value and display.

replace true/false in datagridview columns

I have a datagridview which I fill it as below :
var q= repository.GetStudents();//
dataGridView1.DataSource = null;
dataGridView1.Columns.Clear();
dataGridView1.DataSource = q;
dataGridView1.Columns.RemoveAt(1);
//Remove IsActive
//Cause I want to have my own implementation
dataGridView1.Columns[0].DataPropertyName = "StudentID";
dataGridView1.Columns[0].HeaderText = "Studunet ID";
dataGridView1.Columns[1].DataPropertyName = "IsActive";
dataGridView1.Columns[1].HeaderText = "Status";
The "IsActive" property is of boolean Type. When the "IsActive" cell is being displayed, it show true/false. I want to replace it with my own custom value.
I read this and this posts but I could not resolve my problem.

You can use the CellFormatting event of the DataGridView, e.g.:
void dataGridView_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
{
var grid = (DataGridView)sender;
if (grid.Columns[e.ColumnIndex].Name == "IsActive")
{
e.Value = (bool)e.Value ? "MY_TEXT_FOR_TRUE" : "MY_TEXT_FOR_FALSE";
e.FormattingApplied = true;
}
}
EDIT (as per comment):
It's very similar to what you're doing now, just remove the bound column and add a new column of the desired type and set the DataPropertyName properly e.g. :
this.dataGridView1.Columns.Remove("COL_TO_CUSTOMIZE");
var btnCol = new DataGridViewDisableButtonColumn();
btnCol.Name = "COL_TO_CUSTOMIZE";
btnCol.DataPropertyName = "COL_TO_CUSTOMIZE";
var col = this.dataGridView1.Columns.Add(btnCol);
Note that this append the column at the end, but you can decide the position of the column by using dataGridView.Columns.Insert method instead of Add.

One of the funky things about a DataGridViewComboBoxColumn is that you can give it one data source that has a column of values to lookup and a column of values to show, and you can bind it to another column of values and then it will perform the lookup for you
So, suppose your collection q of Students (or whatever they are) has an IsActive true/false and you want this to show as "All the time", or "Not a chance".. Let's hash together a combobox that does this:
var cb = new DataGridViewComboBoxColumn();
cb.DisplayMember = "DisplayMe"; //the related text to show in the combo
cb.ValueMember = "ValueToLookup"; //the name in the combo's lookup list
cb.DataPropertyName = "IsActive"; //the name of your property on Student, to look up
cb.DataSource = "All the time,Not a Chance"
.Split(',')
.Select(s => new { DisplayMe = s, ValueToLookup = (s[0] == 'A') } )
.ToList();
It doesn't really matter how we generat the combo's datasource; here I've made a string into a List<anonymous_string+bool> by splitting, then selecting a new anonymous type with the two property names I need; you can use anything that has some named properties - a List of KeyValuePair, Tuple, whatever..
The critical thing is that the combo can read the q.IsActive bool you cited in DataPropertyName, look that bool up in its list in the property named in the ValueMember, then display the property named in the DisplayMember. It works for editing too, so the user can choose a new item from the combo and the translation works back the other way - "what does the user choose? what is the value of its property named in ValueMember, put that value into the student IsActive property named in DataPropertyName".. And it doesnt stop at bools either; the value member can be anything - an int, date etc