Working with Data Sets in .NET

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private void dgridParent_CurrentCellChanged(object sender, EventArgs e) { DataTable dtabParent = (DataTable)dgridParentDataSource; DataView dviewChild = (DataView)dgridChildDataSource; dviewChildRowFilter = "CategoryID = " + dtabParentRows[dgridParentCurrentRowIndex]["CategoryID"]; }
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Thus, the DataView class is the key piece in reflecting the parent/child relationship to the user
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6222 Binding to Single-Item Controls
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When asked to display the second form shown in Figure 64 the first form stores a reference to the data set in an Internal variable so that the second form can retrieve it and then displays the second form The second form displays one product row at a time, using Label and TextBox controls This makes it inherently more complex than the first form Binding to singleitem controls is more difficult than binding to multi-item controls for three reasons 1 The user must be given a mechanism to specify which product should be displayed 2 The TextBox controls must display the specified row 3 The TextBox controls can be used to update data as well as display it Data binding to single-valued controls, such as TextBox controls, requires some additional design decisions Making good decisions requires an understanding of data-binding internals So, let s look at the following decisions that must be made and the impacts of each 1 How does the user designate which row is to be displayed a By matching binding Bind the data object to a multi-item control, such as a ComboBox or DataGrid, as well as to the single-item controls, such as the Label and TextBox controls The user selects the desired row from the multi-item control b By indexing Provide a scroll bar or some other position control The user indicates the relative position of the desired row within the data object The application positions to that row
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c By search key Provide a text box The user enters a value The application searches the data object for the row containing the entered value 2 How should that row be assigned to the control a By current row The application designates the desired row as the current row of the data object b By data view The application binds the single-item controls to the data table s DefaultView object and then sets the view s Filter property to limit the view to just the desired row 3 When should the data table be updated with the values from the single-item controls 2 a When the user moves to a new field No It is not necessary to update the data object if the user is continuing to modify other fields of the same row; wait until the user moves to a new row b When the user positions to a new row No Data binding will automatically update the old row values whenever the user moves to a new row c When the user indicates that he or she is finished with the edit (eg, by using a Cancel or Update button or by closing the form) Yes You need to use the data table s CurrencyManager object to complete or cancel the update of the current row if the user exits the operation without moving to a new row The following subsections discuss these three decisions in more detail
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6223 Designating the Row to Be Displayed
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Figure 65 shows the single-item form providing all three methods mentioned previously for designating which row to display We use this form to cover the issues being addressed here It s not the most beautiful form we ever designed, but it does illustrate the functionality we want to cover Matching Binding Of the three designation methods, the easiest to program is matching binding Once you bind the single-item controls and the multi-item controls to the same data object, you no longer have to decide howto assign the row to thesingle-item controls because theuser s selection
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2 The question of when and how the data should be propagated from the data table down to the database is covered later in the Microsoft SQL Server CE and Microsoft SQL Server sections of this chapter
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