Terminal.Gui v2 Overview

A toolkit for building rich console apps for .NET, .NET Core, and Mono that works on Windows, the Mac, and Linux/Unix.

Conceptual Documentation

Features

Cross Platform - Windows, Mac, and Linux. Terminal drivers for Curses, Windows Console, and the .NET Console mean apps will work well on both color and monochrome terminals.
Keyboard and Mouse Input - Both keyboard and mouse input are supported, including support for drag & drop.
Flexible Layout - Supports both Absolute layout and an innovative Computed Layout system. Computed Layout makes it easy to lay out controls relative to each other and enables dynamic terminal UIs.
Clipboard support - Cut, Copy, and Paste of text provided through the Clipboard class.
Arbitrary Views - All visible UI elements are subclasses of the View class, and these in turn can contain an arbitrary number of sub-views.
Advanced App Features - The Mainloop supports processing events, idle handlers, timers, and monitoring file descriptors. Most classes are safe for threading.
Reactive Extensions - Use reactive extensions and benefit from increased code readability, and the ability to apply the MVVM pattern and ReactiveUI data bindings. See the source code of a sample app in order to learn how to achieve this.

Terminal.Gui is a library intended to create console-based applications using C#. The framework has been designed to make it easy to write applications that will work on monochrome terminals, as well as modern color terminals with mouse support.

This library works across Windows, Linux and MacOS.

This library provides a text-based toolkit as works in a way similar to graphic toolkits. There are many controls that can be used to create your applications and it is event based, meaning that you create the user interface, hook up various events and then let the a processing loop run your application, and your code is invoked via one or more callbacks.

The simplest application looks like this:

using Terminal.Gui;

class Demo {
    static int Main ()
    {
        Application.Init ();

        var n = MessageBox.Query (50, 7, 
            "Question", "Do you like console apps?", "Yes", "No");
            
		Application.Shutdown ();
        return n;
    }
}

This example shows a prompt and returns an integer value depending on which value was selected by the user (Yes, No, or if they use chose not to make a decision and instead pressed the ESC key).

More interesting user interfaces can be created by composing some of the various views that are included. In the following sections, you will see how applications are put together.

In the example above, you can see that we have initialized the runtime by calling
Applicaton.Init method in the Application class - this sets up the environment, initializes the color schemes available for your application and clears the screen to start your application.

The Application class, additionally creates an instance of the Toplevel class that is ready to be consumed, this instance is available in the Application.Top property, and can be used like this:

using Terminal.Gui;

class Demo {
    static int Main ()
    {
        Application.Init ();

        var label = new Label ("Hello World") {
            X = Pos.Center (),
            Y = Pos.Center (),
            Height = 1,
        };
        Application.Top.Add (label);
        Application.Run ();
        Application.Shutdown ();
    }
}

Typically, you will want your application to have more than a label, you might want a menu, and a region for your application to live in, the following code does this:

using Terminal.Gui;

class Demo {
    static int Main ()
    {
        Application.Init ();
        var menu = new MenuBar (new MenuBarItem [] {
            new MenuBarItem ("_File", new MenuItem [] {
                new MenuItem ("_Quit", "", () => { 
                    Application.RequestStop (); 
                })
            }),
        });
        
        var win = new Window ("Hello") {
            X = 0,
            Y = 1,
            Width = Dim.Fill (),
            Height = Dim.Fill () - 1
        };

        // Add both menu and win in a single call
        Application.Top.Add (menu, win);
        Application.Run ();
        Application.Shutdown ();
    }
}

Views

All visible elements on a Terminal.Gui application are implemented as Views. Views are self-contained objects that take care of displaying themselves, can receive keyboard and mouse input and participate in the focus mechanism.

See the full list of Views provided by the Terminal.Gui library here.

Every view can contain an arbitrary number of children views. These are called the Subviews. You can add a view to an existing view, by calling the Add method, for example, to add a couple of buttons to a UI, you can do this:

void SetupMyView (View myView)
{
    var label = new Label ("Username: ") {
        X = 1,
        Y = 1,
        Width = 20,
        Height = 1
    };
    myView.Add (label);

    var username = new TextField ("") {
        X = 1,
        Y = 2,
        Width = 30,
        Height = 1
    };
    myView.Add (username);
}

The container of a given view is called the SuperView and it is a property of every View.

Layout

Terminal.Gui supports two different layout systems, absolute and computed \ (controlled by the LayoutStyle property on the view.

The absolute system is used when you want the view to be positioned exactly in one location and want to manually control where the view is. This is done by invoking your View constructor with an argument of type Rect. When you do this, to change the position of the View, you can change the Frame property on the View.

The computed layout system offers a few additional capabilities, like automatic centering, expanding of dimensions and a handful of other features. To use this you construct your object without an initial Frame, but set the X, Y, Width and Height properties after the object has been created.

Examples:


// Dynamically computed
var label = new Label ("Hello") {
    X = 1,
    Y = Pos.Center (),
    Width = Dim.Fill (),
    Height = 1
};

// Absolute position using the provided rectangle
var label2 = new Label (new Rect (1, 2, 20, 1), "World")

The computed layout system does not take integers, instead the X and Y properties are of type Pos and the Width and Height properties are of type Dim both which can be created implicitly from integer values.

The `Pos` Type

The Pos type on X and Y offers a few options:

Absolute position, by passing an integer
Percentage of the parent's view size - Pos.Percent(n)
Anchored from the end of the dimension - AnchorEnd(int margin=0)
Centered, using Center()
Reference the Left (X), Top (Y), Bottom, Right positions of another view

The Pos values can be added or subtracted, like this:

// Set the X coordinate to 10 characters left from the center
view.X = Pos.Center () - 10;

view.Y = Pos.Percent (20);

anotherView.X = AnchorEnd (10);
anotherView.Width = 9;

myView.X = Pos.X (view);
myView.Y = Pos.Bottom (anotherView);

The `Dim` Type

The Dim type is used for the Width and Height properties on the View and offers the following options:

Absolute size, by passing an integer
Percentage of the parent's view size - Dim.Percent(n)
Fill to the end - Dim.Fill ()
Reference the Width or Height of another view

Like, Pos, objects of type Dim can be added an subtracted, like this:

// Set the Width to be 10 characters less than filling 
// the remaining portion of the screen
view.Width = Dim.Fill () - 10;

view.Height = Dim.Percent(20) - 1;

anotherView.Height = Dim.Height (view)+1

TopLevels, Windows and Dialogs.

Among the many kinds of views, you typically will create a Toplevel view (or any of its subclasses), like Window or Dialog which is special kind of views that can be executed modally - that is, the view can take over all input and returns only when the user chooses to complete their work there.

The following sections cover the differences.

TopLevel Views

Toplevel views have no visible user interface elements and occupy an arbitrary portion of the screen.

You would use a toplevel Modal view for example to launch an entire new experience in your application, one where you would have a new top-level menu for example. You typically would add a Menu and a Window to your Toplevel, it would look like this:

using Terminal.Gui;

class Demo {
    static void Edit (string filename)
    {
        var top = new Toplevel () { 
            X = 0, 
            Y = 0, 
            Width = Dim.Fill (), 
            Height = Dim.Fill () 
        };
        var menu = new MenuBar (new MenuBarItem [] {
            new MenuBarItem ("_File", new MenuItem [] {
                new MenuItem ("_Close", "", () => { 
                    Application.RequestStop ();
                })
            }),
        });
        
        // nest a window for the editor
        var win = new Window (filename) {
            X = 0,
            Y = 1,
            Width = Dim.Fill (),
            Height = Dim.Fill () - 1
        };

        var editor = new TextView () {
            X = 0, 
            Y = 0,
            Width = Dim.Fill (),
            Height = Dim.Fill ()
        };
        editor.Text = System.IO.File.ReadAllText (filename);
        win.Add (editor);

        // Add both menu and win in a single call
        top.Add (win, menu);
        Application.Run (top);
        Application.Shutdown ();
    }
}

Window Views

Window views extend the Toplevel view by providing a frame and a title around the toplevel - and can be moved on the screen with the mouse (caveat: code is currently disabled)

From a user interface perspective, you might have more than one Window on the screen at a given time.

Dialogs

Dialog are Window objects that happen to be centered in the middle of the screen.

Dialogs are instances of a Window that are centered in the screen, and are intended to be used modally - that is, they run, and they are expected to return a result before resuming execution of your application.

Dialogs are a subclass of Window and additionally expose the AddButton API which manages the layout of any button passed to it, ensuring that the buttons are at the bottom of the dialog.

Example:

bool okpressed = false;
var ok = new Button("Ok");
var cancel = new Button("Cancel");
var dialog = new Dialog ("Quit", 60, 7, ok, cancel);

Which will show something like this:

+- Quit -----------------------------------------------+
|                                                      |
|                                                      |
|                  [ Ok ] [ Cancel ]                   |
+------------------------------------------------------+

Running Modally

To run your Dialog, Window or Toplevel modally, you will invoke the Application.Run method on the toplevel. It is up to your code and event handlers to invoke the Application.RequestStop() method to terminate the modal execution.

bool okpressed = false;
var ok = new Button(3, 14, "Ok") { 
    Clicked = () => { Application.RequestStop (); okpressed = true; }
};
var cancel = new Button(10, 14, "Cancel") {
    Clicked = () => Application.RequestStop () 
};
var dialog = new Dialog ("Login", 60, 18, ok, cancel);

var entry = new TextField () {
    X = 1, 
    Y = 1,
    Width = Dim.Fill (),
    Height = 1
};
dialog.Add (entry);
Application.Run (dialog);
if (okpressed)
    Console.WriteLine ("The user entered: " + entry.Text);

There is no return value from running modally, so your code will need to have a mechanism of indicating the reason that the execution of the modal dialog was completed, in the case above, the okpressed value is set to true if the user pressed or selected the Ok button.

Input Handling

Every view has a focused view, and if that view has nested views, one of those is the focused view. This is called the focus chain, and at any given time, only one View has the focus.

The library binds the key Tab to focus the next logical view, and the Shift-Tab combination to focus the previous logical view.

Keyboard processing details are available on the Keyboard Event Processing document.

Colors and Color Schemes

All views have been configured with a color scheme that will work both in color terminals as well as the more limited black and white terminals.

The various styles are captured in the Colors class which defined color schemes for the toplevel, the normal views, the menu bar, popup dialog boxes and error dialog boxes, that you can use like this:

Colors.Toplevel
Colors.Base
Colors.Menu
Colors.Dialog
Colors.Error

You can use them for example like this to set the colors for a new Window:

var w = new Window ("Hello");
w.ColorScheme = Colors.Error

The ColorScheme represents four values, the color used for Normal text, the color used for normal text when a view is focused an the colors for the hot-keys both in focused and unfocused modes.

By using ColorSchemes you ensure that your application will work correctbly both in color and black and white terminals.

Some views support setting individual color attributes, you create an attribute for a particular pair of Foreground/Background like this:

var myColor = Application.Driver.MakeAttribute (Color.Blue, Color.Red);
var label = new Label (...);
label.TextColor = myColor

MainLoop, Threads and Input Handling

Detailed description of the mainloop is described on the Event Processing and the Application Main Loop document.

Cross-Platform Drivers

See Cross-platform Driver Model.

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