本文逐步说明如何打印 richtextbox 控件的内容。richtextbox 控件不提供打印其内容的方法。但是，您可以扩展 richtextbox 类以使用 em_formatrange 消息。然后，您可以将 richtextbox 的内容发送到某个输出设备，例如打印机。
创建 richtextboxprintctrl 控件
要扩展 richtextbox 类并使用 em_formatrange 来打印 richtextbox 控件的内容，请按照下列步骤操作： 1. 使用 microsoft visual basic .net 新建一个名为 richtextboxprintctrl 的类库项目。
默认情况下，将创建 class1.vb。
2. 将 class1.vb 文件的名称更改为 richtextboxprintctrl.vb。
3. 在解决方案资源管理器中，右键单击“引用”，然后单击“添加引用”。
4. 在添加引用对话框中，双击“system.drawing.dll”，然后双击“system.windows.forms.dll”。
5. 要添加引用，请单击“确定”。
6. 删除“richtextboxprintctrl.vb”中的现有节点。
7. 将以下代码复制到“richtextboxprintctrl.vb”中：
option explicit on
imports system
imports system.windows.forms
imports system.drawing
imports system.runtime.interopservices
imports system.drawing.printing
namespace richtextboxprintctrl
public class richtextboxprintctrl
inherits richtextbox
convert the unit that is used by the .net framework (1/100 inch)
and the unit that is used by win32 api calls (twips 1/1440 inch)
private const aninch as double = 14.4
<structlayout(layoutkind.sequential)> _
private structure rect
public left as integer
public top as integer
public right as integer
public bottom as integer
end structure
<structlayout(layoutkind.sequential)> _
private structure charrange
public cpmin as integer first character of range (0 for start of doc)
public cpmax as integer last character of range (-1 for end of doc)
end structure
<structlayout(layoutkind.sequential)> _
private structure formatrange
public hdc as intptr actual dc to draw on
public hdctarget as intptr target dc for determining text formatting
public rc as rect region of the dc to draw to (in twips)
public rcpage as rect region of the whole dc (page size) (in twips)
public chrg as charrange range of text to draw (see above declaration)
end structure
private const wm_user as integer = &h400
private const em_formatrange as integer = wm_user + 57
private declare function sendmessage lib "user32" alias "sendmessagea" (byval hwnd as intptr, byval msg as integer, byval wp as intptr, byval lp as intptr) as intptr
render the contents of the richtextbox for printing
return the last character printed + 1 (printing start from this point for next page)
public function print(byval charfrom as integer, byval charto as integer, byval e as printpageeventargs) as integer
mark starting and ending character
dim crange as charrange
crange.cpmin = charfrom
crange.cpmax = charto
calculate the area to render and print
dim recttoprint as rect
recttoprint.top = e.marginbounds.top * aninch
recttoprint.bottom = e.marginbounds.bottom * aninch
recttoprint.left = e.marginbounds.left * aninch
recttoprint.right = e.marginbounds.right * aninch
calculate the size of the page
dim rectpage as rect
rectpage.top = e.pagebounds.top * aninch
rectpage.bottom = e.pagebounds.bottom * aninch
rectpage.left = e.pagebounds.left * aninch
rectpage.right = e.pagebounds.right * aninch
dim hdc as intptr = e.graphics.gethdc()
dim fmtrange as formatrange
fmtrange.chrg = crange indicate character from to character to
fmtrange.hdc = hdc use the same dc for measuring and rendering
fmtrange.hdctarget = hdc point at printer hdc
fmtrange.rc = recttoprint indicate the area on page to print
fmtrange.rcpage = rectpage indicate whole size of page
dim res as intptr = intptr.zero
dim wparam as intptr = intptr.zero
wparam = new intptr(1)
move the pointer to the formatrange structure in memory
dim lparam as intptr = intptr.zero
lparam = marshal.alloccotaskmem(marshal.sizeof(fmtrange))
marshal.structuretoptr(fmtrange, lparam, false)
send the rendered data for printing
res = sendmessage(handle, em_formatrange, wparam, lparam)
free the block of memory allocated
marshal.freecotaskmem(lparam)
release the device context handle obtained by a previous call
e.graphics.releasehdc(hdc)
return last + 1 character printer
return res.toint32()
end function
end class
end namespace
8. 要创建“richtextboxprintctrl.dll”，请在“生成”菜单上单击“生成解决方案”。
测试控件
要测试该控件，请按照下列步骤操作： 1. 使用 visual basic .net 新建一个 windows 应用程序项目。
默认情况下，将创建 form1.vb。
2. 从工具箱中，将一个按钮拖到 form1 上。将名称更改为 btnpagesetup，然后将“文本”更改为页面设置。
3. 从工具箱中，将另一个按钮拖到 form1 上。将名称更改为 btnprintpreview，然后将“文本”更改为打印预览。
4. 从工具箱中，将另一个按钮拖到 form1 上。将名称更改为 btnprint，然后将“文本”更改为打印。
5. 在工具箱中，依次双击“printdialog”、“printpreviewdialog”和“printdocument”，然后双击“pagesetupdialog”将这些控件添加到 form1 中。
6. 将“printdialog1”、“printpreviewdialog1”和“pagesetupdialog1”的 document 属性修改为printdocument1。
7. 在“工具”菜单上，单击“自定义工具箱”。
8. 单击“.net framework 组件”，单击“浏览”，单击以选择“richtextboxprintctrl.dll”，然后单击“确定”。
9. 从工具箱中，将“richtextboxprintctrl”拖到 form1 上。
10. 在解决方案资源管理器中，右键单击“form1.vb”，然后单击“查看代码”。
11. 将以下代码添加到 form1 类中：
private checkprint as integer
private sub printdocument1_beginprint(byval sender as object, byval e as system.drawing.printing.printeventargs) handles printdocument1.beginprint
checkprint = 0
end sub
private sub printdocument1_printpage(byval sender as object, byval e as system.drawing.printing.printpageeventargs) handles printdocument1.printpage
print the content of the richtextbox. store the last character printed.
checkprint = richtextboxprintctrl1.print(checkprint, richtextboxprintctrl1.textlength, e)
look for more pages
if checkprint < richtextboxprintctrl1.textlength then
e.hasmorepages = true
else
e.hasmorepages = false
end if
end sub
private sub btnpagesetup_click(byval sender as system.object, byval e as system.eventargs) handles btnpagesetup.click.click
pagesetupdialog1.showdialog()
end sub
private sub btnprint_click(byval sender as system.object, byval e as system.eventargs) handles btnprint.click
if printdialog1.showdialog() = dialogresult.ok then
printdocument1.print()
end if
end sub
private sub btnprintpreview_click(byval sender as system.object, byval e as system.eventargs) handles btnprintpreview.click
printpreviewdialog1.showdialog()
end sub
12. 要运行该应用程序，请单击“调试”菜单上的“开始”。
13. 在“richtextboxprintctrl”中键入文本。
14. 要设置页面设置，请单击“页面设置”。
15. 要预览该页，请单击“打印预览”。
16. 要打印“richtextboxprintctrl”的内容，请单击“打印”。
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