Changes to the Data Set in Visual Studio .NET

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Changes to the Data Set
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Adding data to the underlying data works in pretty much the same way it did before we started using data binding:
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void addButton_Click(object sender, EventArgs e) { // Add a new row CustomerSetCustomersRow row = thiscustomerSet1CustomersNewCustomersRow(); rowCustomerID = "SELLSB"; thiscustomerSet1CustomersAddCustomersRow(row); // Controls automatically updated // (except some controls, eg ListBox, need a nudge) // NOTE: Use C# "as" cast to ask if the binding // manager is a currency manager If the // result of the "as" cast is null, then // we've got a property manager, which // doesn't have a Refresh method CurrencyManager manager = thisBindingContext[customerSet1, "Customers"] as CurrencyManager; if( manager != null ) managerRefresh(); } Adding a new row to the data set causes most controls to be updated, except for some complex bound controls like the ListBox For those cases, we cast the BindingManagerBase class to a CurrencyManager to be able to call the CurrencyManager-specific Refresh method, which will bring those pesky list boxes up to speed on the new row As far as updates and deletes go, make sure to use the BindingManagerBase class's Current property instead of the Position property to get the current row Otherwise, you could access the wrong row: void updateButton_Click(object sender, EventArgs e) { // Update the current row BindingManagerBase manager = thisBindingContext[customerSet1, "Customers"]; DataRowView view = (DataRowView)managerCurrent; CustomerSetCustomersRow row = (CustomerSetCustomersRow)viewRow; rowContactTitle = "CEO"; // Controls automatically updated } void deleteButton_Click(object sender, EventArgs e) { // Mark the current row as deleted BindingManagerBase manager = thisBindingContext[customerSet1, "Customers"]; DataRowView view = (DataRowView)managerCurrent; CustomerSetCustomersRow row = (CustomerSetCustomersRow)viewRow; rowDelete(); // Controls automatically updated // (no special treatment needed to avoid deleted rows!) } Notice that no code is needed to update the controls to take into account updated or deleted rowsThis is the power of data binding When the underlying data source is updated, we don't want to be forced to update the related controls manually Instead, we bind them and let that happen automatically[4]
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Not all data sources are as good about keeping the bound controls up-to-date as the DataSet-related data sources are For the requirements of a good custom data source, see the "Custom Data Sources" section later in this chapter
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Replacing the Data Set
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Sometimes, after all the data bindings are established, it's necessary to replace a data set with a different data set For example, if you're calling into a Web service that produces a DataSet as the return type, you might find yourself writing code like this: DataSet newDataSet = myWebServiceGetDataSet(); thisdataSet1 = newDataSet; // Data bindings lost Unfortunately, when you replace the existing data set with a new one, all the data bindings remain with the old data set As a shortcut, instead of manually moving all the data bindings to the new data set, you can use the Merge method of the DataSet class to bring the data from the new data set into the existing one: DataSet newDataSet = myWebServiceGetDataSet(); thisdataSet1Clear(); thisdataSet1Merge(newDataSet); // Data bindings kept The trick here is that all the data bindings continue to be bound to the existing data set, but the data from the existing data set is cleared and replaced with the data from the new data set For this to work, all the schema information in the new data set, such as the names of the columns, must match the schema information that the bindings are using Otherwise, you'll get run-time exceptions As an optimization when merging data sets, you'll want to temporarily turn off data binding so that you don't have to update all the bound controls after when the data set is cleared and again when the new data is merged: DataSet newDataSet = myWebServiceGetDataSet(); BindingManagerBase manager = thisBindingContext[dataSet1, "Customers"]; managerSuspendBinding(); thisdataSet1Clear(); thisdataSet1Merge(newDataSet); // Data bindings kept managerResumeBinding(); To turn off the updates that bindings cause as the data set is updated, we suspend the binding by using a call to the binding manager's SuspendBinding method Then, after we clear and merge the data set, to resume updates to the bound controls we resume the binding with the call to ResumeBinding Temporarily suspending bindings isn't for use only with data sets; it's useful whenever the controls shouldn't be updated until a set of operations on the underlying data source has been performed
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