Using External Javascript, CSS or Image File in a WebPart of SharePoint

Button Testbutton;
Image img;
string imagePath;

//
Referring External Javascript
ClientScriptManager cs =
Page.ClientScript;
// Include the required javascript file.
if
(!cs.IsClientScriptIncludeRegistered("jsfile"))
cs.RegisterClientScriptInclude(this.GetType(),
"jsfile", "/_wpresources/MyWP/1.0.0.0_9f4da00116c38ec5/jsfile.js");

Test
:
Testbutton= new Button();
Testbutton.Text = "Click
me";
Testbutton.OnClientClick = "jsfile_Function()"; // specify function name
here
this.Controls.Add(Testbutton);

// Refering External CSS

Microsoft.SharePoint.WebControls.CssLink cssLink = new
Microsoft.SharePoint.WebControls.CssLink();
cssLink.DefaultUrl =
"/_wpresources/MyWP/1.0.0.0_9f4da00116c38ec5/styles.css";
this.Page.Header.Controls.Add(cssLink);

//
Using External Image
imagePath =
"/_wpresources/MyWP/1.0.0.0_9f4da00116c38ec5/Image.jpg";
img.ImageUrl =
imagePath;
img.ID = "image1";

this.Controls.Add(mybutton);

this.Controls.Add(img);