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Render Modes

Some of the Telerik controls support different rendering modes. They can change the actual HTML that is created to facilitate use of CSS3, semantic tags and modern skinning mechanisms. This is controlled through their RenderMode property.

This article contains the following sections:

RenderMode Options

  • Classic - this is the default value. It preserves the original rendering and styling that has been used before, which often means there are a lot of tables used to create layout, which results in nested elements and some markup that can be avoided.

    The Classic Render Mode is in maintenance mode since Q3 2015 and only critical bug fixes are provided for it. All the new functionality, controls and features are developed for the modern Lightweight and Mobile Render Modes.

  • Lightweight - this mode emphasizes on semantic HTML and CSS3. It reduces the amount of markup the control renders (including the depth of the nested elements) and makes it easier to customize. This also reduces the number of image sprites the control uses and the overall size and complexity of each skin, including custom ones.

  • Mobile - this mode is an addition to the adaptive rendering of the Telerik controls. It is intended to utilize the best HTML, accordingly to the device on which the controls are being shown. This mode forces a layout that fits the needs of the touch environment.The differences of this mode are:

    • Larger content text for devices with smaller screens, which improves the user's readability experience;

    • Larger sizes of buttons, touch handles etc. for easier interaction;

    • Greater padding of buttons, touch handles etc. for easier interaction;

  • Auto - this mode makes each control choose the appropriate rendering mode according to the used browser - Classic, Lightweight or Mobile.The behavior of the affected controls depends also on the available render modes, for example in touch devices the mode will be changed automatically to Mobile, if it is supported. If it is not, the mode will fall back until it meets the best mode that fits the environment. This functionality was added in Q3 2013.

    For the automatic RenderMode detection to work, your project must reference the Telerik.Web.Device.Detection.dll assembly.

You can find a list with the controls that support alternative render modes in the Render Modes List help article.

RenderMode Conflict ("mixed render modes")

Only one type of render mode is supported per page for each control type. Otherwise, there will be a RenderMode Conflict leading to distorted appearance of the controls.

Render Modes are applied by sets of styles. Therefore, if multiple instances of the same control are set to use different RenderMode on the same page that will result in styling conflict. The multiple RenderModes will try to apply different styles to the same element and this will lead to appearance issues.

The direct violation of this rule can be easily determined and avoided: For example, all RadButton controls on the page must have the same value set to the RenderMode property. This includes instances from master pages, content pages, and user controls.

In case there is a RadButton in Lightweight render mode on the master page and a RadButton in Classic render mode in the content page, both of RadButton controls will load the styles for its render mode and that is how you get the mixed render mode issue.

Indirect RenderMode Conflict:

Some of the Telerik Controls are complex components consisting of multiple embedded child Controls. This could be a reason for having mixed render even when on the surface of it, there is just one instance of certain control.

Let's clarify that with a sample:

If you have a RadButton in Lightweight and a RadMenu in Classic render mode, there will be no conflicting controls, hence no issue.

If you have a RadGrid in Lightweight and a RadMenu in Classic render mode, then there will be an issue. Why? Because the RadGrid is a complex control and has a RadMenu as a child control. That means you would have a RadGrid and a RadMenu(grid's child) in Lightweight render mode and the standalone RadMenu in Classic render mode. Each of the RadMenu's will load the styles for its render mode and that is how you get the mixed render mode issue.

To determine mixed render mode issue on a page and to avoid it, review the Determine the render mode of all Telerik controls and catch mixed render mode issues KB article.

RenderMode Fallback Order

In some cases setting one value for the RenderMode may result in another mode being used by the controls. This is affected by the UserAgent string of the browser used to request the page. Here follows a list of the various possibilities and how you can affect or predict them.

Classic RenderMode

If you explicitly set this mode, it will never change. It is always the last fallback options available.

Lightweight RenderMode

This mode targets modern browsers (IE8+, Chrome, Firefox, Edge). If the requesting browser is IE7, the controls will fall back to the Classic RenderMode. This often happens if IE runs in Compatibility Mode.

As of R3 2017 you can avoid this by adding the X-UA Compatible header with value IE=edge to the response:

        <add name="X-UA-Compatible" value="IE=Edge"/>
Response.AddHeader("X-UA-Compatible", "IE=Edge"); 

Mobile RenderMode

If the control does not support this mode, it will attempt to use the Lightweight mode.

When set explicitly, this mode will be used even for non-mobile browsers. It is recommended to use the Auto mode for such scenarios because the Mobile modes are tested and supported only under mobile devices.

Auto RenderMode

This mode attempts to fall back to Lightweight in the majority of cases. The exceptions are:

  • The requesting browser is IE7 and the version of the controls is older than R1 2017 and the X-UA Compatible header with value IE=edge is not set. In this case it will fall back to Classic.

  • The requesting browser is identified as a mobile browser and the concrete control provides mobile-specific rendering. In this case it will fall back to Mobile.

Setting Render Mode

There are two ways to set the RenderMode of each Telerik control:

  • Use the RenderMode property each control exposes. When set in the markup you can type in a string, when set in the code-behind it takes a member of the Telerik.Web.UI.RenderMode enum. For example:


    <telerik:RadDock RenderMode="Lightweight" runat="server" ID="RadDock1"></telerik:RadDock>
  • A global setting in the web.config file that will affect the entire application, unless a concrete value is specified for a given control instance:

    • Change render mode for all controls in the application


          <add key="Telerik.Web.UI.RenderMode" value="lightweight" />
    • Change render mode for a given control type:


          <add key="Telerik.Web.UI.Menu.RenderMode" value="lightweight" />

      Where Menu can be replaced with any control name, without Rad.

See Also

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