I have a GridView which loads some data on Load like this:
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
if (!Page.IsPostBack)
{
DataTable dataSource = LoadObjects();
gvObjects.DataSource = dataSource;
}
}
I've also added a SelectedIndexChanged event handler where I want to perform some functions whenever a row is selected. The problem is that unless I remove the IsPostBack check from the OnLoad method, when a row is selected the GridView.SelectedRow attribute is not the row I selected.
Ideally I don't want to load all my data from the database on each postback. Are there any best-practices to get the selected row during the SelectedIndexChanged event without reloading everything again?
Thanks.
I usually have my GridViews full of dynamic controls which can be a lot of "fun", if they're not recreated on PostBack they don't work.
You seem only interested in the SelectedRow but this solution will also work and help save you a headache if you start getting fancy with dynamic controls
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
gvObjects.DataSource = LoadCachedObjects();
gvObjects.DataBind();
}
private DataTable LoadCachedObjects()
{
var result = new DataTable();
if ((Session["CachedDataTable"] != null) && (IsPostBack))
{
//cached DataTable will only be used on PostBack
result = Session["CachedDataTable"] as DataTable;
}
if (result.Rows.Count == 0)
{
result = LoadObjects(); //Get data from the database
Session["CachedDataTable"] = result;
}
return result;
}
This only loads the data from the session when a postback event occurs, so you'll have one initial database hit on page load. Also if you end up using that code on other pages you don't have to be massively concerned about giving the session variable a unique name
By default the GridView selects a row based on Index. Try instructing the GridView to select rows based on Keys.
Set the EnablePersistedSelection property to true so that the row selection is based on data-key values. Now if your earlier selected row gets its index or position changed in any way it will remain selected.
If you can't prevent postbacks, you will obviously have to reload.
So the solution would be to try to reload as little as possible.
A good way is to cache data somewhere, for example in the Session object.
But only cache the primary keys together with a result index (1 to total result count). This way, you can quickly retrieve the primary keys that you need data for, and get only that data freshly from the database.
Related
I want to add value into a Grid view via dropdownlist with a button.
I want the ddTN.SelectedItem.value in the Grid view to be unique. No duplication
How do I check every row for the ddTN.SelectedItem.value before adding a new ddTN.SelectedItem.value into the Grid view?
This are the codes that I have and it keep comparing the value with the first value in the gridview. Not the others.
I don't want to use a checkbox and such. All the example I found required using checkbox.
protected void Insert(object sender, EventArgs e)
{
int i = 0;
var p = 1;
DataControlFieldCell cell = GridView1.Rows[i].Cells[p] as DataControlFieldCell;
if (cell.Text != ddTN.SelectedItem.Value)
{
dt.Rows.Add(ddTN.SelectedValue, ddDuration.SelectedValue);
ViewState["Customers"] = dt;
this.BindGrid();
label.Text = "";
p++;
}
else
{
label.Text = "Exercise already inserted";
}
}
It looks like you were intending on looping over the items in the grid but you have forgotten the looping mechanism. In your code, it always only checks the first item because i is initialized to 0 and never changes.
Try using a looping mechanism like a for loop or a while loop. Or, if you know the items in the grid from the beginning, perhaps use a hash table for quickly checking if the selected item already exists.
Keep trying, you are almost there!
As stated here the DataBindingComplete event for a DataGridView is fired whenever the contents of the data source change, or a property such as DataSource changes. This results in the method being called multiple times.
I am currently using the DataBindingComplete event to do some visual formatting to my form. For example, I make the text in the first column (column 0) appear as Row Headers and then hide that column (see code below).
private void grdComponents_DataBindingComplete(object sender, DataGridViewBindingCompleteEventArgs e)
{
foreach (DataGridViewRow row in grdComponents.Rows)
{
row.HeaderCell.Value = row.Cells[0].Value.ToString();
}
grdComponents.Columns[0].Visible = false;
// do more stuff...
}
It is unnecessary to execute this code more than once, and I am looking to put it into a place where that can happen. Unfortunately it didn't work when I added the snippet to the end of my form's Load method (after I set the DataSource of my DataGridView), nor did it work in the DataSourceChanged event.
Yes, you can use DataSourceChanged event, but be aware, that it occurs only when data source is changed. Additionally, DataBindingComplete offers you information why it has happend - through e.ListChangedType:
Reset = 0,// Much of the list has changed. Any listening controls should refresh all their data from the list.
ItemAdded = 1,// An item added to the list
ItemDeleted = 2,// An item deleted from the list.
ItemMoved = 3,// An item moved within the list.
ItemChanged = 4,// An item changed in the list.
PropertyDescriptorAdded = 5,// A System.ComponentModel.PropertyDescriptor was added, which changed the schema.
PropertyDescriptorDeleted = 6,// A System.ComponentModel.PropertyDescriptor was deleted, which changed the schema.
PropertyDescriptorChanged = 7// A System.ComponentModel.PropertyDescriptor was changed, which changed the schema.
According to this answer:
https://social.msdn.microsoft.com/forums/windows/en-us/50c4f46d-c3b8-4da7-b08f-a751dca12afd/databindingcomplete-event-is-been-called-twice
the whole thing happens because you don't have DataMember property set in your dataGridView. And you can set it only if you want to set particular table from database which is set as your DataSource of dataGridView. Other way - throws an exception.
The simplest way will be just to execute this code once:
Add a flag like Boolean isDataGridFormatted in your form.
And check it like
private void grdComponents_DataBindingComplete(object sender, DataGridViewBindingCompleteEventArgs e)
{
if (this.isDataGridFormatted )
return;
foreach (DataGridViewRow row in grdComponents.Rows)
{
row.HeaderCell.Value = row.Cells[0].Value.ToString();
}
grdComponents.Columns[0].Visible = false;
// do more stuff...
this.isDataGridFormatted = false;
}
A bit better will be to prepare your DataGridView during the form construction. As I understand your columns won't change during the course of your program but you don't want to initialize everything manually. You could load some dummy one-item(one-row) data during the initialization:
private void Initialize_DataGridView()
{
// Add dummy data to generate the columns
this.dataGridView_Items.DataContext = new Item[]{ new Item {Id = 5, Value = 6}};
// Make your formatting
foreach (DataGridViewRow row in grdComponents.Rows)
{
row.HeaderCell.Value = row.Cells[0].Value.ToString();
}
grdComponents.Columns[0].Visible = false;
// Reset the dummy data
this.dataGridView_Items.DataContext = null; // Or new Item[]{};
}
...
public MyForm()
{
Initialize();
this.Initialize_DataGridView();
}
I am not sure that exactly such code will work with dataGridView but it is close enough.
Of course an event would have been a nearly ideal solution but there's hardly any that deals with successful autogeneration of columns http://msdn.microsoft.com/en-us/library/system.windows.forms.datagridview_events(v=vs.110).aspx except the AutoGenerateColumnChanged but that is not what we need.
While it is possible to use the ColumnAdded - it will probably execute only once foreach of the autogenerated column, the actual implementation could become an overkill and will be even less direct than already mentioned approaches.
If you will have some time and desire you could create your own DataGridView derived class, take Boolean isDataGridFormatted from your form and implement all the initialization(or event hooking) inside the custom DataGridView.
I want to perform operation that On a button click event , Grid Currentrow entire data is passed to an object array
I have tried to search through following links :
DataGridView selecting a specific row and retrieving its values
Getting data from selected datagridview row and which event?
But they are talking about particular cell value
i tried to perform with code
DataRowView currentDataRowView = (DataRowView)grdGLSearch.CurrentRow.DataBoundItem;
DataRow row1 = currentDataRowView.Row;
But currentDataRowView is retrieving null
one of My Senior succesfully created a generic property GetSelectedRow()
it works like this :
var object =grdGLSearch.GetSelectedRow<T>();
and it has definition
public T GetSelectedRow<T>()
{
if (this.CurrentRowIndex == -1)
{
return default(T);
}
return (base.DataSource as BindingList<T>)[this.CurrentRowIndex];
}
But it is binded to only one Main grid , i also want to use this property to another Grids
I dont want data of a particular column , i want entire row data .. and dont want any iteration to be perform ...
Is there any single liner operation for this ?
Please suggest if I am missing any links
Since you are only showing 2 lines of code, I am really not sure exactly what is going on. First off, I get you want the entire row when you click some button. However, you never state how the current row is being selected.
In order to get the full selected row, you must have a selected cell. The MSDN documentation says this on the page for DataGridView.SelectedRow. So I am assuming that the user will click a cell, and you want the entire row. I would create a variable that will hold your selected row. Then when the user clicks the cell, automatically select the row and save it. Then when the button is clicked, just retrieve the the already saved row.
private DataGridViewRow selectedRow { get; set; }
Then have the event for when the user clicks a cell
private void grdGLSearch_CellClick(object sender, DataGridViewCellEventArgs e)
{
selectedRow = grdGLSearch.Rows[e.RowIndex];
}
Finally, the button click event
private void SubmitBtn_ItemClick(object sender, ItemClickEventArgs e)
{
// to target the specific data
var cellVal1 = selectedRow.Cells["SpecificCell1"].Value;
var cellVal2 = selectedRow.Cells["SpecificCell2"].Value;
}
I am having a problem updating a datatable that is bound to a datagrid. Tried a bunch of approaches but the problem is the underlying datatable reverts back to its initial state everytime u click a command.
Here's the example code:
On Label Click:
protected void OnUserDataGridCommand(object source, DataGridCommandEventArgs e)
{
DataTable dt = DataGridUsers.DataSource as DataTable;
if (e.CommandName == "Lock Out")
{
// Approach 1
e.Item.Cells[0].Text = "Lock";
DataGridUsers.DataSource = dt;
DataGridUsers.DataBind();
// Approach 2
dt.Rows[e.Item.ItemIndex]["FirstName"] = "LOCK";
dt.Rows[e.Item.ItemIndex].AcceptChanges();
DataGridUsers.DataSource = dt;
DataGridUsers.DataBind();
}
}
So this will update the row's first name to say Lock but when you click on another row the previously Locked will revert to the first name. When I breakpoint regardless of a row displaying lock, the datatable always is the initial data (no "LOCK" data).
This line typically doesn't work for me
DataTable dt = DataGridUsers.DataSource as DataTable;
You might want to instead manage the DataSource in the session, by retrieving it out of session doing your modifications and then rebind it to the Grid.
You might also want to take a look at where the DataSource got bound to the grid the first time. Is is it running on the postback thus overwriting your changes.
I want an OpenFileDialog to come up when a user clicks on a cell, then display the result in the cell.
It all works, except that the DataGridView displays an extra row, for adding values to the list it's bound to. The row shows up if dataGridView.AllowUserToAddNewRows == true, which is what I want. What I don't want is for the application to crash when that row is edited programatically; instead, it should do exactly what it would do if the user had edited that row manually (add the new row to the underlying list, push another empty row onto the grid for adding values).
I read about SendKeys.Send(), which should make the DataGridView behave exactly as though the user had typed the value in; however, it does not work either. Here is what I am trying:
if (openFileDialog1.ShowDialog() == DialogResult.OK)
{
dataGridView1.CurrentCell = cell;
//simply doing a cell.Value = etc. will cause the program to crash
cell.ReadOnly = false;
dataGridView1.Columns[cell.ColumnIndex].ReadOnly = false;
dataGridView1.EditMode = DataGridViewEditMode.EditOnEnter;
dataGridView1.BeginEdit(true);
SendKeys.Send(openFileDialog1.FileName + "{Enter}");
dataGridView1.EndEdit();
cell.ReadOnly = true;
dataGridView1.Columns[cell.ColumnIndex].ReadOnly = true;
}
//I would expect the FileName would be in the cell now, and a new empty
//row tacked onto the end of the DataGridView, but it's not; the DataGridView
//is not changed at all.
I found a workaround on this page, though I don't know why it works
public MyForm()
{
InitializeComponent();
//Create a BindingSource, set its DataSource to my list,
//set the DataGrid's DataSource to the BindindingSource...
_bindingSource.AddingNew += OnAddingNewToBindingSource;
}
private void OnAddingNewToBindingSource(object sender, AddingNewEventArgs e)
{
if(dataGridView1.Rows.Count == _bindingSource.Count)
{
_bindingSource.RemoveAt(_bindingSource.Count - 1);
}
}
I'm getting very sick of spending so much time dealing with Visual Studio bugs...
I was having the same problem when trying to programattically edit cells with a binding source.
""Operation is not valid due to the current state of the object"
Which operation? What State? So helpful.
My code seem to work fine except when editing the last row in the grid.
Turns out the key is DataGridView.NotifiyCurrentCelldirty(true)
The correct sequence for programatically editing a cell, so it works the same as if the user did it.
(A new empty row appears when changing a cell in the last row) is something like this:
1) Make the cell to edit the current cell (do what ever you need to the current currentcell, first
like calling endEdit if it is in edit mode.)
2) Call DataGridview.BeginEdit(false)
3) Call DataGridView.NotifyCurrentCellDirty(true)
4) Modify the value.
5) Call DataGridView.EndEdit()
And you'll want to do something for the RowValidating and RowValidated events.
One of my routines for updating a cell value looks like this:
This is from a method in my class derived from DataGridView.
You could do the same thing from the containing form, calling
through a DataGridView instance, because the methods are public.
Here the calls are using an impliciit 'this.'
private void EnterTime()
{
if (CurrentRow == null) return;
SaveCurrentCell(); // Calls EndEdit() if CurrentCell.IsInEditMode
DataGridViewCell previous = CurrentCell;
CurrentCell = CurrentRow.Cells[CatchForm.TimeColumn];
BeginEdit(false);
NotifyCurrentCellDirty(true);
CurrentCell.Value = DateTime.Now;
EndEdit();
CurrentCell = previous;
}
I’m not sure why a separate call is needed.
Why doesn’t BeginEdit, or actually modifying the cell value, cause the right
things to happen?
And if you move the NotifyCurrentCellDirty call to after you actually modify the cell,
it doesn’t behave correctly either. All very annoying.
This is old, but I am running VS2010 and just come across this issue. I have a DataGridView bound to a List<T> using a BindingList<T>. I have a drag n' drop event on my DataGridView and it would throw this exception after deleting all rows from the DGV (except for the last blank one which one cannot delete) and then adding new rows to the DGV in the DragDrop handler via the BindingList<T>. This exception was not thrown if I simply added rows manually editing individual cells.
One solution I read said to handle the BindingList<T>.AddNew event, but I found that this event did not fire when calling BindingList<T>.Add() within the DragDrop event handler (I'm not sure why). I solved the issue by adding
if(bindingList.Count == 0)
bindingList.RemoveAt(0)
inside of the DragDrop event handler before adding new objects to bindingList. It seemed that adding an object to the bindingList failed when the only "object" in the bindingList was the one associated to the final blank row. The point of a BindingList<T> is to allow the developer to work with it instead of the DGV directly, but it seems doing so can cause problems in border cases.
The relationship between DGV rows and BindingList<T> rows seems to be a bit of a gray area. I have not spent much time investigating this, but it is not clear to me what is the state of the "object" in the BindingList<T> associated to the final (empty) row of the DGV. However, it does seem like the "object" at the end is only instantiated "correctly" when you interact with the final row directly (not via a DataSource).
Try this:
if (openFileDialog1.ShowDialog() == DialogResult.OK)
{
int row = e.RowIndex;
int clmn = e.ColumnIndex;
if(e.RowIndex == dataGridView1.Rows.Count- 1)
dataGridView1.Rows.Add();
dataGridView1.Rows[row].Cells[clmn].Value = openFileDialog1.FileName;
}
EDIT
I didn't notice that you are binding your datagridview :(
Ok, to solve it: use binding source, set its DataSource property to your list, then set the data source of the data grid view to this binding source. Now, the code should look like so:
public partial class frmTestDataGridView : Form
{
BindingSource bindingSource1 = new BindingSource();
List<string> datasource = new List<string>();
public frmTestDataGridView()
{
InitializeComponent();
datasource.Add("item1");
datasource.Add("item2");
datasource.Add("item3");
bindingSource1.DataSource = datasource;
dataGridView1.DataSource = bindingSource1;
}
private void dataGridView1_CellClick(object sender, DataGridViewCellEventArgs e)
{
if (openFileDialog1.ShowDialog() == DialogResult.OK)
{
int row = e.RowIndex;
int clmn = e.ColumnIndex;
if (e.RowIndex == dataGridView1.Rows.Count - 1)
{
bindingSource1.Add("");
}
dataGridView1.Rows[row].Cells[clmn].Value = openFileDialog1.FileName;
}
}
}
Remember to use Row.BeginEdit() and Row.EndEdit() if you get this error while editing a value in a row, using DataGrid or GridEX from Janus (in my case). The sample code that Darrel Lee posted here (https://stackoverflow.com/a/9143590/1278771) remind me to use these instructions that I forgot to use and this solved the problem for me.