This is not the very first time I am digging this subject but this is the first time I feel like I don’t know nothing. I am going to start from scratch and explore different technics on this subject…and again, I will use Amit Kalani’s book. This book will help me explore the following concepts :
- Simple Data Binding
- Complex Data Binding
- One-way and two-way Data Binding
- The BindingContext object
- The Data Form Wizard
Simple Data Binding
Simple data binding means connecting a single value from the data model to a single property of a control. For example, you might bind the Vendor object name from a list of vendors to the Text property of a TextBox control.
private void SimpleBindingForm_Load(object sender, System.EventArgs e)
{
// Create an array of vendor names
String [] astrVendorNames = {"Microsoft", "Rational", "Premia"};
// Bind the array to the text box
txtVendorName.DataBindings.Add("Text", astrVendorNames, "");
}
The Binding class can accept many other types of data sources, including the following:
- An instance of any class that implements the IBindingList or ITypedList interface, including the DataSet, DataTable, DataView, and DataViewManager classes.
- An instance of any class that implements the IList interface on an indexed collection of objects. In particular, this applies to classes that inherit from System.Array, including C# arrays.
- An instance of any class that implements the IList interface on an indexed collection of strongly typed objects. For example, you can bind to an array of Vendor objects
Binding to a collection of strongly typed objects is a convenient way to handle data from an object-oriented data model.
private void SimpleBindingForm_Load(object sender, System.EventArgs e)
{
// Initialize the vendors array
aVendors[0] = new Vendor("Microsoft");
aVendors[1] = new Vendor("Rational");
aVendors[2] = new Vendor("Premia");
// Bind the array to the textbox
txtVendorName.DataBindings.Add("Text", aVendors, "VendorName");
}
Navigating through data, using BindingContext :
private void btnPrevious_Click(object sender, System.EventArgs e)
{
// Move to the previous item in the data source
this.BindingContext[aVendors].Position -= 1;
}
private void btnNext_Click(object sender, System.EventArgs e)
{
// Move to the next item in the data source
this.BindingContext[aVendors].Position += 1;
}
Complex Data Binding
In complex data binding, you bind a user interface control to an entire collection of data, rather than to a single data item. A good example of complex data binding involves the DataGrid control. Obviously, complex data binding is a powerful tool for transferring large amounts of data from a data model to a user interface.code
private void ComplexBindingForm_Load(object sender, System.EventArgs e)
{
// Create an array of exams
Exam[] aExams =
{
new Exam("315", "Web Applications With Visual C# .NET"),
new Exam("316", "Windows Applications With Visual C# .NET"),
new Exam("320", "XML With Visual C# .NET"),
new Exam("305", "Web Applications With VB.NET"),
new Exam("306", "Windows Applications With VB.NET"),
new Exam("310", "XML With VB.NET")
};
// Bind the array to the list box
lbExams.DataSource = aExams;
lbExams.DisplayMember = "ExamName";
lbExams.ValueMember = "ExamNumber";
// Create an array of candidates
Candidate[] aCandidates = {
new Candidate("Bill Gates", "305"),
new Candidate("Steve Ballmer", "320")};
// Bind the candidates to the text boxes
txtCandidateName.DataBindings.Add( "Text", aCandidates, "CandidateName");
txtExamNumber.DataBindings.Add( "Text", aCandidates, "ExamNumber");
// And bind the exam number to the list box value
lbExams.DataBindings.Add( "SelectedValue", aCandidates, "ExamNumber");
In this example Exam class could be any user defined type you can think of, as long as it supports String properties ExamNumber and ExamName like this one:
public class Exam
{
private String examNumber;
private String examName;
public String ExamNumber
{
get{ return examNumber;}
}
public String ExamName
{
get{ return examName;}
}
public Exam(String strExamNumber, String strExamName)
{
examNumber = strExamNumber;
examName = strExamName;
}
}
And Candidate is also something similar to the following:
public class Candidate
{
private string examNumber;
private string candidateName;
public string ExamNumber
{
get {return examNumber;}
set {examNumber = value;}
}
public string CandidateName
{
get {return candidateName;}
set {candidateName = value;}
}
public Candidate(String strCandidateName, String strExamNumber)
{
this.CandidateName = strCandidateName;
this.ExamNumber = strExamNumber;
}
}
Filtering With DataView Objects
A DataSet object contains two collections. The Tables collection is made up of DataTable objects, each of which represents a single table in the data source. The Relatios collection is made up of DataRelation objects, each of whic represents the relationship between two DataTable objects.
A DataView represents a bindable, customized view of a DataTable object.You can sort them or filter the records of a DataTable object to build a DataView Object. private void FilterGridView_Load(object sender, System.EventArgs e)
{
// Move the data from the database to the DataSet
sqlDataAdapter1.Fill(dsCustomers1, "Customers");
// Create a dataview to filter the Customers table
System.Data.DataView dvCustomers = new System.Data.DataView(dsCustomers1.Tables["Customers"]);
// Apply a sort to the dataview
dvCustomers.Sort = "ContactName";
// Apply a filter to the dataview
dvCustomers.RowFilter = "Country = 'France'";
// and bind the results to the grid
dgCustomers.DataSource = dvCustomers;
}
This way of retrieving data is consuming lots of network resources and to bring all the records of a table to the client prior to filtering it doesn’t seem an efficient way of using (available?) resources. Therefor it is wise to create the view and on the database server and filter it before sending it to client.
A very nice example of binding is to bind a textbox to the collection within the combobox. This dead-easy sample is binding the text property of the TextBox to a combobox using its SelectedObject attribute. txtRAM.DataBindings.Add(“Text”, cmbComputers, “SelectedValue”);
Currency Manager
One new challenge I was face with recently is ability of dinamically load a grid based on the selection on one other grid. This is usefull when for example you have to tables loaded and you want to be able to navigate the first table and when move the cursor from one record to the other, the second grid which is related by a foreign key to the first one, gets filtered.This can be achieved in several ways. I just found one very easy way using the BindingContext and CurrencyManager.Let’s say you have a data view keeping the data about the parent relation and you will assign a grid to it like this: DataView dvParent = base.DataSet.Tables[0].DefaultView ;
...
dgCodeGroup.DataSource = dvParent ;
What you need to do here is to get a reference to the ContextManager which is available through the BindingContext:
myCurrencyManager = (CurrencyManager)this.BindingContext[dvParent];
myCurrencyManager.PositionChanged +=new EventHandler(OnCurrencyManager_PositionChanged);
Now all you need to do is to filter your second grid based on the selection. And the selection is easy to find:
DataRowView drv = (DataRowView) myCurrencyManager.Current ;
This is a collection of fields in that row. So you can use it to get into the fields and build your second data view.
Navigating the Current Position
This is where the CurrencyManager comes very handy. It has a property called Position which you can access to figure out the index and you can also assign a value to reposition it. Also the Count property is very handy to avoid moving out of boundries.
private void MoveNext(CurrencyManager myCurrencyManager)
{
if(myCurrencyManager.Count == 0)
{
Console.WriteLine("No records to move to."); return;
}
if (myCurrencyManager.Position == myCurrencyManager.Count - 1)
{ Console.WriteLine("You're at end of the records"); }
else
{ myCurrencyManager.Position += 1; }
}
private void MoveFirst(CurrencyManager myCurrencyManager)
{ if(myCurrencyManager.Count == 0)
{ Console.WriteLine("No records to move to.");
return;
}
myCurrencyManager.Position = 0;}
private void MovePrevious(CurrencyManager myCurrencyManager)
{ if(myCurrencyManager.Count == 0)
{ Console.WriteLine("No records to move to.");
return;
}
if(myCurrencyManager.Position == 0)
{ Console.WriteLine("You're at the beginning of the records."); }
else{ myCurrencyManager.Position -= 1; }}private void MoveLast(CurrencyManager myCurrencyManager){ if(myCurrencyManager.Count == 0) { Console.WriteLine("No records to move to.");
return;
}
myCurrencyManager.Position = myCurrencyManager.Count - 1;}