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Frequently asked questions

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Alex Maitland edited this page Dec 10, 2019 · 134 revisions

Quick FAQ TOC

This FAQ tries to showcase some cool CefSharp features and some of the most common gotcha's. For an in-depth guide to many of the features please read General Usage Guide.

For more hints see the growing list of issues labelled as faq-able!

1. How do you call a JavaScript method from .NET?

See General Usage Guide - How do you call a JavaScript method

When can I start executing JavaScript?

See General Usage Guide - When can I start executing JavaScript

2. How do you call a JavaScript method that return a result?

See General Usage Guide - How do you call a Javascript method that return a result?

3. How do you expose a .NET class to JavaScript?

See General Usage Guide - How do I expose a .Net class

4. Why do I get an error about "Could not load file or assembly 'CefSharp.Core.dll' or one of its dependencies. The specified module could not be found." when trying to run my CefSharp-based application? It compiles successfully, but does not run? It runs on my developer machine, though throws an exception when I copy it to another computer?

This is a common error, typically one of the following

  1. VC++ 2013/2015 Redistributable Package is required in order to run CefSharp on non developer machines. See FAQ #6 below for more information. You can include the required dlls as part of your application.
  2. Not all dependencies are present in the executing folder. CefSharp includes unmanaged dll's and resources, these are copied to the executing folder via two .props file which are included in your project when you install the Nuget packages. See list of required files below, make sure the required files are present.
  3. You packaged your application for distribution via an installer and it doesn't run on the target machine. Installers don't include the unmanaged resources by default, you'll need to add them manually. For ClickOnce, see #1314 for some pointers and solutions other users have come up with.
  4. "Generate serialization assembly" is set to "On" or "Auto" in Properties->Build tab. Setting this to "Off" seems to resolve the issue.

A list of required files can be found here: Output files description (Redistribution)

NOTE: This also applies if you get a FileNotFoundException when initializing the WPF control in XAML.

NOTE 2: If compiling from source (not recommended, use the Nuget packages) and you notice that you can no longer build in debug mode, but release builds work just fine you may need to repair your version of Visual Studio. This happens in rare cases where you will get the same exact message as a missing unmanaged .dll file as shown above.

5. Why does the Visual Studio WPF designer not work when I add a ChromiumWebBrowser to my app?

Version 57.0.0 adds minimal designer support, see https://github.com/cefsharp/CefSharp/pull/1989 for details.

6. How do I include the Visual Studio C++ 2012/2013/2015 redistributables with my application?

CefSharp requires the Microsoft VC++ Runtime.

CefSharp Version VC++ Version .Net Version
65.0.0 and above 2015 4.5.2
51.0.0 to 63.0.0 2013 4.5.2
45.0.0 to 49.0.0 2013 4.0.0
43.0.0 and below 2012 4.0.0

For Microsoft's official guide see Redistributing Visual C++ Files on MSDN. To download visit Visual Studio C++ 2012/2013/2015 redistributables

A brief summary of your options for installing/including VC++ with your application are:

  • Install the Microsoft Visual C++ Redistributable Package on every machine on which you wish to run your CefSharp based application. Once installed updates can then be managed via Windows Update.
  • You can either set the Visual Studio C++ redistributables as pre-requisites of the installer (i.e. ClickOnce or WiX Toolset)
  • Copying over to your project the contents of this folder (Only present if you have the matching version of Visual Studio installed on your computer):
# For VC++ 2012 (x86)
C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\redist\x86\Microsoft.VC110.CRT
# For VC++ 2012 (x64)
C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\redist\x64\Microsoft.VC110.CRT

# For VC++ 2013 (x86)
C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\redist\x86\Microsoft.VC120.CRT
# For VC++ 2013 (x64)
C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\redist\x64\Microsoft.VC120.CRT

# For VC++ 2015 (x86)
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\redist\x86\Microsoft.VC140.CRT
# For VC++ 2015 (x64)
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\redist\x64\Microsoft.VC140.CRT

With the 3rd approach you won't need to install the prerequisite Visual C++ 2012/2013/2015 Runtime Files to your client. If you build your own from source what you deploy of course has to match your build environment. For the official Nuget releases see the Releases Branches table for details.

For VC++ 2013 JetBrains have a Microsoft.VC120.CRT.JetBrains package on Nuget.org, appears to include the relevant files, you would still need to hook up some sort of post build task to copy them to your bin folder.

For VC++ 2015 you may also need to package the Universal CRT, see the Distributing Software that uses the Universal CRT section of https://blogs.msdn.microsoft.com/vcblog/2015/03/03/introducing-the-universal-crt/ the last dot point titled App-local deployment of the Universal CRT is supported has details. Windows 10 includes the Universal CRT as an operating system component and there is no need to copy those files. UPDATE: See also https://docs.microsoft.com/en-us/cpp/windows/universal-crt-deployment?view=vs-2019

Note When building from source make sure you compile in Release mode when deploying to machines that don't have Visual Studio installed. Visual C++ uses a different set of run-time libraries for Debug and Release builds. The Debug run-time libraries are only installed with Visual Studio. If you use the official Nuget packages they're already built in Release mode and you can subsequently build your app in debug mode as only the Visual C++ projects need to be compiled in Release mode.

7. How do I override Javascript window.alert actions and similar?

Implement IJsDialogHandler and assign your instance to the browser.JsDialogHandler property of the ChromiumWebBrowser instance to override the default behaviour.

8. Where are the CefSharp3 binaries?

CefSharp3 is released as Nuget packages. Please see https://github.com/cefsharp/CefSharp/blob/master/README.md#nuget-packages for the latest stable and pre-release versions.

For a very simple example projects using the NuGet packages, see the CefSharp.MinimalExample repository. Clone it/download the source if you want a really small and simple example of how CefSharp3 can be used.

_Please Note: Platform Target
CefSharp supports AnyCPU for version 51.0.0 and above, see https://github.com/cefsharp/CefSharp/issues/1714 for details.

The simplest option to get up and running quickly is to either select x86 or x64. See Steps to configure your solution here.

9. Windows XP/2003 Support

Chromium has removed support for Windows XP/2003. It is no longer possible to run CefSharp on a computer running Windows XP/2003. Please don't create new issues related to Windows XP. The following https://github.com/cefsharp/CefSharp/wiki/Windows-XP-No-Longer-Supported Wiki page may be useful and can be edited by anyone with a GitHub account, so feel free to contribute any information you think may prove useful.

10. What files do I need to include when I redistribute an application that uses CefSharp?

See: Output files description (Redistribution)

11. Build process can't copy CEF files

Sometimes the build process can't copy CEF files and will retry many times before it finally fails. This happens when CefSharp.BrowserSubprocess.exe is still running even though the application was closed.
The solution is to manually kill the CefSharp.BrowserSubprocess.exe using i.e. Task Manager.

12. Why does IndexedDB return a QuotaExceededError?

When working with IndexedDB you must set the CefSettings CachePath to a directory where the current user has write access. In most cases you can use code like this to create a cache directory and pass the setting to Cef during Initialize():

// On Win7 this will create a directory in AppData.
var cache = System.IO.Path.Combine(Environment.GetFolderPath (Environment.SpecialFolder.ApplicationData), System.IO.Path.Combine("MyApplication","cache"));
if (!System.IO.Directory.Exists (cache))
    System.IO.Directory.CreateDirectory (cache);

// Set the CachePath during initialization.
var settings = new CefSettings(){CachePath = cache};
Cef.Initialize (settings);

13. How do you handle a Javascript event in C#?

THIS SECTION IS OUTDATED AND NEEDS TO BE REWRITTEN This section can be greatly simplified using https://github.com/cefsharp/CefSharp/issues/2775 It is no longer nessicary to bind an object, you simply need to execute some javascript that subscribs to the event your are interested in and call CefSharp.PostMessage(message); in javascript and in .Net browser.JavascriptMessageReceived event.

public class BoundObject
{
    public void OnFrameLoadEnd (object sender, FrameLoadEndEventArgs e)
    {
      if(e.Frame.IsMain)
      {
        browser.ExecuteScriptAsync(@"
          document.body.onmouseup = function()
          {
            bound.onSelected(window.getSelection().toString());
          }
        ");
      }
    }

    public void OnSelected(string selected)
    {
        MessageBox.Show("The user selected some text [" + selected + "]");
    }
}

// ...

// After your ChromiumWebBrowser has been instantiated (for WPF directly after `InitializeComponent();` in the control constructor).
var obj = new BoundObject();
browser.RegisterJsObject("bound", obj);
browser.FrameLoadEnd += obj.OnFrameLoadEnd ;

Please note:

  • RegisterJsObject should be called directly after you create an instance of ChromiumWebBrowser
  • "bound" is the name of the object that will be created as a top-level object accessible to any JS scripts running on the webpage. You can use whatever you like, but ensure it does not conflict with an existing JS object, and that the names match in C# and JS.
  • This sample injects JS code into the webpage on-the-fly using the FrameLoadEnd event. If you have control of the webpage, you can simply add the JS code into the webpage.
  • We call the OnSelected C# method with a single string argument. You can use any number of arguments, or none, but they must all be primitive types.
  • Ensure you cast complex JS objects to strings or convert them to JSON when passing them.
  • Since CefSharp will be searching for the method OnSelected by its name, ensure your obfuscator does NOT rename the method to something else, or it will not be executed.

14. How can I implement WinForms drag & drop?

One possible solution is outlined in https://github.com/cefsharp/CefSharp/issues/1593#issuecomment-304451518

15. WPF blurry rendering

There are two common reasons the browser will render incorrectly

High DPI

If your app is running on a HighDPI enabled display/monitor. You will need to make your application DPI Aware, see https://github.com/cefsharp/CefSharp/wiki/General-Usage#high-dpi-displayssupport

Rounding/BitmapScaling

WPF represents width/height using the double data type, this causes problems as CEF uses int for width/height values. It's necessary to cast double to int, UseLayoutRounding is enabled by default on the ChromiumWebBrowser control to have the values rounded to whole pixel values by WPF. UseLayoutRounding is inherited by child elements, so it's possible for a parent element to override the UseLayoutRounding setting.

  • Try setting UseLayoutRounding=true on the parent of the ChromiumWebBrowser or even on an ancestor up the visual tree as this has helped others in the past.

  • UseLayoutRounding disables anti-aliasing for children, so set it to false for the children of the container where you want to keep the anti-aliasing, see #166

  • Every frame is rendered as a bitmap, the default BitmapScalingMode used is HighQuality

  • Changing RenderOptions.BitmapScalingModetoNearestNeighbor` may also work

Visual Studios Live XAML Debugger is very useful in determining the root cause of the problem.

Anyone with a GitHub account can edit this wiki, contributions are encouraged and welcomed.

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