Haxe - 为什么我不能在没有得到父级没有给定属性的错误的情况下访问子属性？

Question

I've recently been getting into Haxe and just started to use HaxeFlixel to load a Tiled .TMX file.

I am creating a TiledMap object and passing it the TMX file path, then I want to iterate over the layers in that object to add them to the game scene. However when I try to access .tileArray (which is a property of TiledTileLayer) I get the following error :-

flixel.addons.editors.tiled.TiledLayer has no field tileArray

Here is the code:

package;

import flixel.FlxState;
import flixel.tile.FlxTilemap;
import flixel.addons.editors.tiled.TiledMap;
import openfl.Assets;


class PlayState extends FlxState
{
    private var _tiled_map:TiledMap;

    override public function create():Void
    {
        _tiled_map = new TiledMap("assets/data/Map1.tmx");

        for(layer in _tiled_map.layers){
            var layerData:Array<Int> = layer.tileArray;
        }

        super.create();
    }

    override public function update(elapsed:Float):Void
    {
        super.update(elapsed);
    }
}

I've found the following example - http://coinflipstudios.com/devblog/?p=182 which seems to work fine for people.

So I wanted to check whether the layer object was a TiledTileLayer as it should be, or TiledLayer, with the following:

trace(Type.typeof(layer));

Which sure enough yields:

PlayState.hx:24: TClass([class TiledTileLayer])

So if it is a TiledTileLayer which has the field tileArray why is it moaning?

I had a look at the source code ( https://github.com/HaxeFlixel/flixel-addons/blob/dev/flixel/addons/editors/tiled/TiledMap.hx#L135 ) and TiledTileLayer inherits from TiledLayer. Layers is an array of type TiledLayer, so I think this is why it is moaning. I can clearly see that the array is storing child objects of TiledLayer, but as soon as I access any props/methods of those children, it complains that the parent does not have that field? Very confusing!

To run I'm using this command: C:\\HaxeToolkit\\haxe\\haxelib.exe run lime test flash -debug -Dfdb

Thank you!

Answer 1

So if it is a TiledTileLayer which has the field tileArray why is it moaning?

It may be a TiledTileLayer in this case, but that may not always be the case. layers is an Array<TileLayer> after all, so it could be a TiledObjectLayer or a TiledImageLayer as well (which don't have a tileArray field). This can nicely be seen in the code you linked . The concrete type can only be known at runtime, but the error you get happens at compile-time.

If you know for sure there won't be any object or image layers, you can just cast it to a TiledTileLayer . However, just to be safe, it's good practice to check the type beforehand anyway:

for (layer in _tiled_map.layers) {
    if (Std.is(layer, TiledTileLayer)) {
        var tileLayer:TiledTileLayer = cast layer;
        var layerData:Array<Int> = tileLayer.tileArray;
    }
}

It works without this for the tutorial you linked because it was made for an older version of flixel-addons.