如何使用haskell在Gtk4中显示视频？

Question

我正在尝试使用 Gtk4 和 Haskell 显示视频，但我在执行此操作时遇到了一些问题。 这是到目前为止我的代码。我已经修改了 https://github.com/haskell-gi/haskell-gi/blob/master/examples/Gtk4/gtk4-example.hs 中的示例，现在我有了这个。

{-# LANGUAGE OverloadedStrings, OverloadedLabels, ImplicitParams #-}

import Control.Monad (void)
import System.Environment (getArgs, getProgName)

import Data.Int (Int32)

import qualified GI.Gtk as Gtk
import Data.GI.Base

activate :: Gtk.Application -> IO ()
activate app = do

  --img1 <- Gtk.pictureNewForFilename (Just ("D:/stack-projects/gtk-intro-twelve/redbus"))
  --img3 <- "D:/stack-projects/gtk-intro-twelve/Glossaryck-4.png"
  --img2 <- Gtk.pictureGetFile img3
  --img <- Gtk.pictureSetFilename (Just "D:/stack-projects/gtk-intro-twelve/Glossaryck-4.png")

  video1 <- Gtk.pictureNewForPaintable (Just ("D:/stack-projects/gtk-intro-twelve/redbus.mp4"))

  -- #append box img1

  window <- new Gtk.ApplicationWindow [#application := app,
                                       #title := "Hello",
                                       #child := video1]
  #setDefaultSize window 1427 1080
  #show window

main :: IO ()
main = do
  app <- new Gtk.Application [#applicationId := "haskell-gi.Gtk4.test",
                              On #activate (activate ?self)]

  -- If the application does not need to parse command line arguments
  -- just pass Nothing.
  args <- getArgs
  progName <- getProgName
  void $ #run app (Just $ progName : args)

我首先尝试使用

img1 <- Gtk.pictureNewForFilename (Just ("D:/stack-projects/gtk-intro-twelve/Glossaryck-4.png"))

在屏幕上打印图像，并且成功了。 然后我尝试用

img1 <- Gtk.pictureNewForFilename (Just ("D:/stack-projects/gtk-intro-twelve/redbus.mp4"))

执行相同的操作来输出请求的视频，但它不起作用。

然后我尝试使用

video1 <- Gtk.pictureNewForPaintable (Just ("D:/stack-projects/gtk-intro-twelve/redbus.mp4"))

但它引发了错误

D:\stack-projects\gtk-intro-twelve\app\Main.hs:19:13: error: [GHC-10283]
    * Couldn't match representation of type `a0'
                               with that of `ManagedPtr ()'
        arising from a superclass required to satisfy `Coercible
                                                         a0 (ManagedPtr ())',
        arising from a superclass required to satisfy `ManagedPtrNewtype
                                                         a0',
        arising from a superclass required to satisfy `GObject a0',
        arising from a use of `Gtk.pictureNewForPaintable'
    * In a stmt of a 'do' block:
        video1 <- Gtk.pictureNewForPaintable
                    (Just ("D:/stack-projects/gtk-intro-twelve/redbus.mp4"))
      In the expression:
        do video1 <- Gtk.pictureNewForPaintable
                       (Just ("D:/stack-projects/gtk-intro-twelve/redbus.mp4"))
           window <- new
                       Gtk.ApplicationWindow
                       [#application := app, #title := "Hello", ....]
           #setDefaultSize window 1427 1080
           #show window
      In an equation for `activate':
          activate app
            = do video1 <- Gtk.pictureNewForPaintable
                             (Just ("D:/stack-projects/gtk-intro-twelve/redbus.mp4"))
                 window <- new Gtk.ApplicationWindow [#application := app, ....]
                 #setDefaultSize window 1427 1080
                 ....
   |
19 |   video1 <- Gtk.pictureNewForPaintable (Just ("D:/stack-projects/gtk-intro-twelve/redbus.mp4"))
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^

Error: [S-7282]
       Stack failed to execute the build plan.

我不知道这意味着什么。我猜这与 GObject 有关，事实上我应该首先将变量

video1

转换为 GObject？但我不太确定。你能指出我正确的方向吗？

Answer 1

大概你应该使用

videoNewForFilename

而不是

pictureNewForFilename

。