It maintains a mapping of error messages associated to each control in the form. If you set an error message for a control, then an error icon is shown next to the control and will also display a tooltip when you hover the mouse over the error icon.
You set the error message for a control by calling the SetError method on the error provider instance. You can validate down in the Control hierarchy by using the Validate and ValidateChildren method on container controls such as Forms. In order to capture errors in DataSet and DataTable objects, you need to query the HasErrors Boolean property to check if there are rows with errors.
If HasErrors is set to true, then you must iterate over the data set's Tables collection to determine which table has data with errors by checking the HasErrors Boolean property of each table. For a table that returns true to HasError property, if you want to explore for the errors, then you can call the GetErrors method on the DataTable object, which will return an array of DataRow objects containing the rows with errors.
You can check the RowError property for each row to get additional information as well as to call GetColumnsInError method to get back an array of DataColumns, which you can then use to call the GetColumnError to extract the individual error message. Because an instance of TextBox control manages its Text property as a string, the result value can be anything.
Thus the ValidatingTextBox extends TextBox class adding new functionality to the base control, such as the responsibility of checking the format of the input text according to the intended data type to be associated. This new control ValidatingTextBox might also check whether the input is required or not. Finally, this new features of the ValidatingText are generic enough and they allow implementing a number of basic requirements. First of all, create a new Class Library project, and a delete the default class, and finally add a new class ValidatingTextBox which inherits from the base TextBox control as well as a references to the System.
Forms and System. Drawing assemblies. We add four attributes and the underlying properties to the class. One to set the desired data type the control is going to validate, the second one to set whether or not to check if the end-user has entered a data value, the third one is a reference to a ErrorProvider control which shows the error message to the end-user and the fourth one is the custom error message see Listing 1. Here, I evaluate the input value according to a correct value based on the data type selected by the property DataType.
In order to check the correct format of the input value, then I use the TryParse method against the target data type. If this method returns TRUE, then the input text is correct formatted against the target data type, otherwise the input value does not conform to the constraints of the target data type. The code for the custom Validating event is shown in Listing 2. IsNullOrEmpty this. Date this. DateTime this. TryParse this.
Trim , out dummy ;. If you assigned EnablePreventFocusChange , canceling the event will cause the Validated event not to occur. Input focus will remain on the current control until the user changes the data to a valid format.
If you assigned EnableAllowFocusChange , the Validated event won't occur when you cancel the event, but focus will still change to the next control. Assigning Disable to the AutoValidate property prevents implicit validation altogether.
To validate your controls, you'll have to use explicit validation. The explicit validation approach validates data at one time. You can validate the data in response to a user action, such as clicking a Save button or a Next link. When the user action occurs, you can trigger explicit validation in one of the following ways:.
Different Windows Forms controls have different defaults for their AutoValidate property. The following table shows the most common controls and their defaults.
When a control maintains focus because the data it contains is invalid, it's impossible to close the parent form in one of the usual ways:. However, in some cases, you might want to let the user close the form regardless of whether the values in the controls are valid.
You can override validation and close a form that still contains invalid data by creating a handler for the form's FormClosing event. In the event, set the Cancel property to false. This forces the form to close.
For more information and an example, see Form. If you force the form to close in this manner, any data in the form's controls that has not already been saved is lost.
In addition, modal forms don't validate the contents of controls when they're closed. You can still use control validation to lock focus to a control, but you don't have to be concerned about the behavior associated with closing the form. Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode. Overview of how to validate user input Windows Forms. Please rate your experience Yes No. Any additional feedback?
If an error description string is specified for the control, an icon appears next to the control. Next, a dd the click event handler to the Login button as the following c code.
Add the validating event handler to the TextBox allows you to check validate the TextBox control. Using c errorprovider check if error through the Validating event handler. To clear error provider c you can call the SetError method, then set value to null. If you want to change icon errorprovider c , you can add an imagelist control to your winform, then set icon to the error provider control as the following c code.
You can also change the blink style to NeverBlink if you don't want to scare the user.
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