Testing

plasmawindowed

There are 3 ways to test a widget.

1. plasmawindowed can be used if the widget is installed to:
   ~/.local/share/plasma/plasmoids
   It will remember any changes you make to the config as this is the same command used for "Windowed widgets" like the "Calculator" app. It has limited features for displaying the widget, but the command should be preinstalled.
2. plasmoidviewer, explained further down, can display a widget as a desktop widget, or a panel widget. You can also test a widget that is not yet installed. You will need to first install the plasma-sdk package to use it.
3. Install the widget and add it to your panel. Restarting plasma every time using:
   plasmashell --replace
   I only recommend this testing method for a final test as it takes a few seconds for the panel to load.

plasmawindowed --help

Usage: plasmawindowed [options] applet [args...]
Plasma Windowed

Options:
  --statusnotifier  Makes the plasmoid stay alive in the Notification Area,
                    even when the window is closed.
  -v, --version     Displays version information.
  -h, --help        Displays this help.

Arguments:
  applet            The applet to open.
  args              Arguments to pass to the plasmoid.

Run the following to test the Application Launcher widget:

plasmawindowed org.kde.plasma.kickoff

plasmoidviewer

If you haven't yet, install the plasma-sdk package with sudo apt install plasma-sdk.

plasmoidviewer --help

Usage: plasmoidviewer [options]
Run Plasma widgets in their own window

Options:
  -v, --version                    Displays version information.
  -c, --containment <containment>  The name of the containment plugin
  -a, --applet <applet>            The name of the applet plugin
  -f, --formfactor <formfactor>    The formfactor to use (horizontal, vertical,
                                   mediacenter, planar or application)
  -l, --location <location>        The location constraint to start the
                                   Containment with (floating, desktop,
                                   fullscreen, topedge, bottomedge, leftedge,
                                   rightedge)
  -x, --xPosition <xPosition>      Set the x position of the plasmoidviewer on
                                   the plasma desktop
  -y, --yPosition <yPosition>      Set the y position of the plasmoidviewer on
                                   the plasma desktop
  -s, --size <widthXheight>        Set the window size of the plasmoidview
  -p, --pixmapcache <size>         The size in kB to set the pixmap cache to
  -t, --theme <themeName>          The name of the theme which the shell will
                                   use
  -h, --help                       Displays this help.

You can test an installed widget by using its plugin id.

plasmoidviewer -a org.kde.plasma.kickoff

Or use it to run a widget in a specific folder. This is particularly useful for development as you can now skip the install step.

plasmoidviewer -a ~/Code/plasmoid-helloworld/package

Test as Desktop Widget

Note that --location=desktop is used for the desktop wallpaper, not desktop widgets. Desktop widgets use --location=floating.

plasmoidviewer -a package --location=floating --formfactor=planar
plasmoidviewer -a package -l=floating -f=planar
plasmoidviewer -a package # floating+planar is the default.

Test as Horizontal Panel Widget

If we set plasmoidviewer's plasmoid.formFactor to be horizontal and plasmoid.location to the topedge or bottomedge, we can test a widget focusing in the panel.

plasmoidviewer -a package -l topedge -f horizontal

Testing DPI Scaling

By setting the QT_SCALE_FACTOR=2 environment variable we can double the DPI value from 96 to 192 just for the plasmoidviewer window. This is great for testing if your code will support a HiDPI screen.

If you're testing a very high DPI, you'll probably find the default plasmoidviewer window is too small to show the widget, so we'll set the size and position of the window. Note that the window will go maximized if you set a size larger than you screen has available.

QT_SCALE_FACTOR=2 plasmoidviewer -a package
QT_SCALE_FACTOR=2 plasmoidviewer -a package -l topedge -f horizontal -x 0 -y 0 -s 1920x1080

Enable logging

By default in Qt 5.9, QML's console.log(), which used to write a string to stdout (the terminal output), is hidden by default.

You can see console.log() output with the following environment variable command:

QT_LOGGING_RULES="qml.debug=true" plasmawindowed org.kde.plasma.kickoff
QT_LOGGING_RULES="qml.debug=true" plasmoidviewer -a org.kde.plasma.kickoff
QT_LOGGING_RULES="qml.debug=true" plasmashell --replace

However it is much easier to always have it shown for the current user, including in the system log (journalctl -b0 -f). To do so, we need to set [Rules] qml.debug=true in ~/.config/QtProject/qtlogging.ini. You can easily set it by running this kwriteconfig5 command:

kwriteconfig5 --file ~/.config/QtProject/qtlogging.ini --group "Rules" --key "qml.debug" "true"

# ~/.config/QtProject/qtlogging.ini
[Rules]
qml.debug=true

You should now see output when you add console.log() statements to your widget. You can place them in any function like the Component.onCompleted signal handler.

Item {
    Component.onCompleted: {
        console.log("Hello World")
    }
}

Or in a onPropertyChanged signal. The following example will print a log message when you click the button.

import QtQuick 2.0
import QtQuick.Layouts 1.0
import org.kde.plasma.components 3.0 as PlasmaComponents
import org.kde.plasma.plasmoid 2.0
PlasmaComponents.Button {
    id: widget
    Plasmoid.preferredRepresentation: Plasmoid.fullRepresentation
    Layout.minimumWidth: implicitWidth

    property int num: 1
    onNumChanged: console.log('num', num)

    text: i18n("Add 1")
    onClicked: num += 1
}