This means that the Eval function is for reading purposes only. On the other hand, the Bind function allows users to control display values as well as update or modify the data. In some programming languages, the full form of Eval is English evaluate. It is a function that can evaluate a string as well as return corresponding results as if the string were an expression.
The input to Eval may also be a structured representation of code instead of a string. In computer programming, to make associations between two or more programming items or value objects means to Bind. This is done only for some extent of time and place.
In simple terms, while building an application, lots of routines, subroutines, classes, and modules are used. To bind means to put these pieces together. In some programming languages, Eval is a function that can be employed to evaluate a certain string. Along with this, it also yields the corresponding results just as though the string were an expression. Another way to understand what Eval is is by considering that Eval is a method of binding that allows a user to control only the display value.
Eval carries out only one-way binding. With Eval, a user is not able to update or modify the display value in any way. The method is protected and defined on the Template control class. Moreover, Eval does not require any sort of ID of certain controls.
Although you can use the Bind method to retrieve the value of the data-bound field just like the Eval method, when the data can be modified, you still need to use the Bind method. In ASP. NET, data-bound controls such as GridView, DetailsView, and FormView controls can automatically use the update, delete, and insert operations of the data source control.
The data source control will then execute the appropriate database commands. The Bind method is commonly used with input controls, such as the TextBox control rendered by the GridView row in edit mode.
When the data-bound control creates these input controls as part of its presentation, this method can extract the input values. The Bind method takes the name of the data field as a parameter and thus associates it with the binding attribute,. However, in some cases, you need to explicitly call the DataBind method to perform the binding. One of these situations is when you use the DataSource property not the DataSourceID property to bind a control to a data source control.
In this case, you need to explicitly call the DataBind method to perform data binding and parse data binding expressions. Another situation is when you need to manually refresh the data in the data-bound control. Suppose there is a page with two controls, both of which display information from the same database may use different views. In this case, you may need to explicitly rebind the control to the data to keep the data display synchronized. For example, there may be a GridView control that displays a list of products, and a DetailsView control that allows the user to edit a single product.
Although the data displayed by the GridView and DetailsView controls come from the same data source, they are bound to different data source controls because the two controls use different queries to obtain their data. The user may use the DetailsView control to update the record, causing the associated data source control to perform the update.
Therefore, after the DetailsView control updates the data, you can call the DataBind method. In this way, the GridView control will reflect the updates made by the DetailsView control. Using binding to a lookup table A common solution for data-bound controls is to allow users to use the DropDownList control or other list controls to select a value from the lookup table to update or insert the value. In this case, bind the lookup control to a separate data source that returns a list of possible values, and bind the selected value of the lookup control to a field in the parent data binding row.
You can add this function as follows. Then bind the SelectedValue property of the lookup control to the relevant field in the data source of the container control.
Second, set the DataSourceID property of the lookup control to a data source control that can retrieve the lookup value.
Then set the DataTextField property of the lookup control to the field in the lookup table that contains the value to be displayed, and set its DataValueField property to the field in the lookup table that contains the unique identifier of the lookup value if applicable. As a matter fact, ASP. NET web pages are considered to be the basic building blocks for different advanced web applications. Web pages with the extension of.
NET allows more functional freedom and greater flexibility for the programmers. Databinding, templates and creation of customized columns in ASP. NET requires one to use Eval and Bind methods in order to bind controls. The usage of Eval method is for read-only purposes, which means that a user can only control the display values. The Bind method on the other hand allows the users to modify and update data — the values entered in a column can be changed or altered through TextBox and CheckBox controls.
This is the basic difference between Eval and Bind — a template can be edited, changed, modified or deleted with the usage of Bind method, whereas the Eval method allows one to only enter the desired values. Databinding syntax allows users to insert, modify, alter, change, retrieve or delete data from a template or column on a webpage.
The data expression in the controls such as FormView, GridView etc.
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