Question

I cant seem to figure out how to create a simple NSOutlineView with 2 columns, and a datastructure that is more than 1 level deep (a hierachy).

I’ve been researching this for days, and all I can find is Objective C examples, which I really can’t use for anything.

I understand there are different patterns for doing this, one being the DataSource pattern. I tried creating a class that inherited from NSOutlineViewDataSource, however thats all I got, I have no clue on what I should do next!

Lets say I would like to display the following class in my NSOutlineView:

public class Person
{
    public string Name {get;set;} // First column
    public int Age {get;set} // Second column
    public List<Person> Children {get;set} // Children
}

What would be the most trivial approach to accomplishing this?

Answer 1

Brace yourselves… A level-independant NSOutlineView in MonoMac!

After hundreds of google searches, and looking through ObjC as well as C# code, I finally figured out how to do it! I will post my solution here, in case someone else needs it.

This may or may not be the best way to do it, but it works for me.

---

Step 1: In Interface Builder, add an NSOutlineView. Add 2 columns to it, and set their Identifier to colName, and colAge.

Also, while you’re at it, add a button to your form.

---

Step 2: Create an outlet for the NSOutlineView – I called mine lvMain because I come from a VCL background. Also, create an action for your button (this will be the onClick handler).

---

Step 3: Save your XIB file, and return to Mono – it will update your project file. Now, we want to create the model we wish to use for our view.

For this example, I will use a simple Person object:

public class Person:NSObject
{
    public string Name {
        get;
        set;
    }

    public int Age {
        get;
        set;
    }

    public List<Person> Children {
        get;
        set;
    }

    public Person (string name, int age)
    {
        Name = name;
        Age = age;
        Children = new List<Person>();
    }
}

Nothing overly complicated there.

---

Step 4: Create the datasource. For this example, this is what I made:

public class MyDataSource:NSOutlineViewDataSource
{
    /// The list of persons (top level)
    public List<Person> Persons {
        get;
        set;
    }
    // Constructor
    public MyDataSource()
    {
        // Create the Persons list
        Persons = new List<Person>();
    }

    public override int GetChildrenCount (NSOutlineView outlineView, NSObject item)
    {
        // If the item is not null, return the child count of our item
        if(item != null)
            return (item as Person).Children.Count;
        // Its null, that means its asking for our root element count.
        return Persons.Count();
    }

    public override NSObject GetObjectValue (NSOutlineView outlineView, NSTableColumn forTableColumn, NSObject byItem)
    {
        // Is it null? (It really shouldnt be...)
        if (byItem != null) {
            // Jackpot, typecast to our Person object
            var p = ((Person)byItem);
            // Get the table column identifier
            var ident = forTableColumn.Identifier.ToString();
            // We return the appropriate information for each column
            if (ident == "colName") {
                return (NSString)p.Name;
            }
            if (ident == "colAge") {
                return (NSString)p.Age.ToString();
            }
        }
        // Oh well.. errors dont have to be THAT depressing..
        return (NSString)"Not enough jQuery";
    }

    public override NSObject GetChild (NSOutlineView outlineView, int childIndex, NSObject ofItem)
    {
        // If the item is null, it's asking for a root element. I had serious trouble figuring this out...
        if(ofItem == null)
            return Persons[childIndex];
        // Return the child its asking for.
        return (NSObject)((ofItem as Person).Children[childIndex]);
    }

    public override bool ItemExpandable (NSOutlineView outlineView, NSObject item)
    {
        // Straight forward - it wants to know if its expandable.
        if(item == null)
            return false;
        return (item as Person).Children.Count > 0;
    }
}

---

Step 5 – The best step: Bind the datasource and add dummy data! We also wanna refresh our view each time we add a new element. This can probably be optimized, but I’m still in the “Oh my god its working” zone, so I currently don’t care.

            // Our Click Action
    partial void btnClick (NSObject sender)
    {
        var p = new Person("John Doe",18);
        p.Children.Add(new Person("Jane Doe",10));
        var ds = lvMain.DataSource as MyDataSource;
        ds.Persons.Add(p);
        lvMain.ReloadData();
    }

    public override void AwakeFromNib ()
    {
        base.AwakeFromNib ();
        lvMain.DataSource = new MyDataSource();

    }

---

I hope this information can help the troubled souls of the MonoMac newcomers like myself.