Godot接口

通常,需要依赖于功能的其他对象的脚本。这个过程分为两部分:

  1. 获取对可能具有这些功能的对象的引用。
  2. 从对象访问数据或逻辑。

本教程的其余部分,概述了完成所有这些操作的各种方法。

获取对象引用

对所有 Object 来说,引用它们最基本的方法,是从另一个获取的实例中,获取对现有对象的引用。

var obj = node.object # Property access.
var obj = node.get_object() # Method access.
Object obj = node.Object; // Property access.
Object obj = node.GetObject(); // Method access.

同样的原则也适用于 Reference 对象。虽然用户经常以这种方式访问 NodeResource,还可以采取其他措施。

代替属性或方法访问,可以通过加载访问获得 Resource

var preres = preload(path) # Load resource during scene load
var res = load(path) # Load resource when program reaches statement

# Note that users load scenes and scripts, by convention, with PascalCase
# names (like typenames), often into constants.
const MyScene : = preload("my_scene.tscn") as PackedScene # Static load
const MyScript : = preload("my_script.gd") as Script

# This type's value varies, i.e. it is a variable, so it uses snake_case.
export(Script) var script_type: Script

# If need an "export const var" (which doesn't exist), use a conditional
# setter for a tool script that checks if it's executing in the editor.
tool # Must place at top of file.

# Must configure from the editor, defaults to null.
export(Script) var const_script setget set_const_script
func set_const_script(value):
    if Engine.is_editor_hint():
        const_script = value

# Warn users if the value hasn't been set.
func _get_configuration_warning():
    if not const_script:
        return "Must initialize property 'const_script'."
    return ""
// Tool script added for the sake of the "const [Export]" example.
[Tool]
public MyType : extends Object
{
    // Property initializations load during Script instancing, i.e. .new().
    // No "preload" loads during scene load exists in C#.

    // Initialize with a value. Editable at runtime.
    public Script MyScript = GD.Load<Script>("MyScript.cs");

    // Initialize with same value. Value cannot be changed.
    public readonly Script MyConstScript = GD.Load<Script>("MyScript.cs");

    // Like 'readonly' due to inaccessible setter.
    // But, value can be set during constructor, i.e. MyType().
    public Script Library { get; } = GD.Load<Script>("res://addons/plugin/library.gd");

    // If need a "const [Export]" (which doesn't exist), use a
    // conditional setter for a tool script that checks if it's executing
    // in the editor.
    private PackedScene _enemyScn;

    [Export]
    public PackedScene EnemyScn
    {
        get { return _enemyScn; }
        set
        {
            if (Engine.IsEditorHint())
            {
                _enemyScn = value;
            }
        }
    };

    // Warn users if the value hasn't been set.
    public String _GetConfigurationWarning()
    {
        if (EnemyScn == null)
            return "Must initialize property 'EnemyScn'.";
        return "";
    }
}

请注意以下几点:

  1. 一种语言可以通过多种方式加载这些资源。
  2. 在设计对象如何访问数据时,不要忘记,还可以将资源作为引用传递。
  3. 请记住,加载资源将获取引擎维护的缓存资源实例。要获取一个新对象,必须 复制 一个现有引用,或者使用 new() 从头实例化一个引用。

节点也有一个可选的访问点:场景树。

extends Node

# Slow.
func dynamic_lookup_with_dynamic_nodepath():
    print(get_node("Child"))

# Faster. GDScript only.
func dynamic_lookup_with_cached_nodepath():
    print($Child)

# Fastest. Doesn't break if node moves later.
# Note that `onready` keyword is GDScript only.
# Other languages must do...
#     var child
#     func _ready():
#         child = get_node("Child")
onready var child = $Child
func lookup_and_cache_for_future_access():
    print(child)

# Delegate reference assignment to an external source
# Con: need to perform a validation check
# Pro: node makes no requirements of its external structure.
#      'prop' can come from anywhere.
var prop
func call_me_after_prop_is_initialized_by_parent():
    # Validate prop in one of three ways.

    # Fail with no notification.
    if not prop:
        return

    # Fail with an error message.
    if not prop:
        printerr("'prop' wasn't initialized")
        return

    # Fail and terminate.
    # Compiled scripts in final binary do not include assert statements
    assert prop.

# Use an autoload.
# Dangerous for typical nodes, but useful for true singleton nodes
# that manage their own data and don't interfere with other objects.
func reference_a_global_autoloaded_variable():
    print(globals)
    print(globals.prop)
    print(globals.my_getter())
public class MyNode
{
    // Slow, dynamic lookup with dynamic NodePath.
    public void Method1()
    {
        GD.Print(GetNode(NodePath("Child")));
    }

    // Fastest. Lookup node and cache for future access.
    // Doesn't break if node moves later.
    public Node Child;
    public void _Ready()
    {
        Child = GetNode(NodePath("Child"));
    }
    public void Method2()
    {
        GD.Print(Child);
    }

    // Delegate reference assignment to an external source
    // Con: need to perform a validation check
    // Pro: node makes no requirements of its external structure.
    //      'prop' can come from anywhere.
    public object Prop;
    public void CallMeAfterPropIsInitializedByParent()
    {
        // Validate prop in one of three ways.

        // Fail with no notification.
        if (prop == null)
        {
            return;
        }

        // Fail with an error message.
        if (prop == null)
        {
            GD.PrintErr("'Prop' wasn't initialized");
            return;
        }

        // Fail and terminate.
        Debug.Assert(Prop, "'Prop' wasn't initialized");
    }

    // Use an autoload.
    // Dangerous for typical nodes, but useful for true singleton nodes
    // that manage their own data and don't interfere with other objects.
    public void ReferenceAGlobalAutoloadedVariable()
    {
        Node globals = GetNode(NodePath("/root/Globals"));
        GD.Print(globals);
        GD.Print(globals.prop);
        GD.Print(globals.my_getter());
    }
};

从对象访问数据或逻辑

Godot的脚本API是鸭子类型。这意味着,如果脚本执行操作,则Godot不会通过 类型 验证其是否支持该操作。相反,它检查对象是否 实现 了单个方法。

例如,CanvasItem 类有一个 visible 的属性。实际上,脚本API公开的所有属性,都是绑定到名称的 settergetter 对。如果有人试图访问 CanvasItem.visible,那么Godot会按照以下顺序进行检查:

  • 如果对象附加了脚本,它将尝试通过脚本设置属性。通过覆盖属性的 setter 方法,这为脚本提供了覆盖基础对象上定义的属性的机会。
  • 如果脚本没有该属性,它在 ClassDB 中对 CanvasItem 类及其所有继承的类型执行 visible 属性的哈希表查找。如果找到,它将调用绑定的 settergetter。有关哈希表的更多信息,参见 数据偏好 文档。
  • 如果没有找到,它会进行显式检查,以查看用户是否要访问 scriptmeta 属性。
  • 如果没有,它将在 CanvasItem 及其继承的类型中检查 _set/_get 实现(取决于访问类型)。这些方法可以执行逻辑,从而给人一种对象具有属性的印象。_get_property_list 方法也是如此。
    • 请注意,即使对于非合法的符号名称,例如 TileSet1/tile_name 属性,这种情况也会发生。这是指ID为1的 tile 的名称,即 TileSet.tile_get_name(1)

因此,这个鸭子类型的系统可以在脚本、对象的类、或对象继承的任何类、但只能用于扩展Object的对象中,定位属性。

Godot提供了多种选项,来对这些访问,执行运行时检查:

  • 鸭子类型属性的访问。这些将进行属性检查(如上所述)。如果对象不支持该操作,则执行将停止。

    # All Objects have duck-typed get, set, and call wrapper methods.
    get_parent().set("visible", false)
    
    # Using a symbol accessor, rather than a string in the method call,
    # will implicitly call the `set` method which, in turn, calls the
    # setter method bound to the property through the property lookup
    # sequence.
    get_parent().visible = false
    
    # Note that if one defines a _set and _get that describe a property's
    # existence, but the property isn't recognized in any _get_property_list
    # method, then the set() and get() methods will work, but the symbol
    # access will claim it can't find the property.
    
    // All Objects have duck-typed Get, Set, and Call wrapper methods.
    GetParent().Set("visible", false);
    
    // C# is a static language, so it has no dynamic symbol access, e.g.
    // `GetParent().Visible = false` won't work.
    
  • 一个方法检查。在 CanvasItem.visible 的情况下,我们可以像访问任何其他方法一样,访问这些方法,set_visibleis_visible

    var child = get_child(0)
    
    # Dynamic lookup.
    child.call("set_visible", false)
    
    # Symbol-based dynamic lookup.
    # GDScript aliases this into a 'call' method behind the scenes.
    child.set_visible(false)
    
    # Dynamic lookup, checks for method existence first.
    if child.has("set_visible"):
        child.set_visible(false)
    
    # Cast check, followed by dynamic lookup
    # Useful when you make multiple "safe" calls knowing that the class
    # implements them all. No need for repeated checks.
    # Tricky if one executes a cast check for a user-defined type as it
    # forces more dependencies.
    if child is CanvasItem:
        child.set_visible(false)
        child.show_on_top = true
    
    # If one does not wish to fail these checks without notifying users, one
    # can use an assert instead. These will trigger runtime errors
    # immediately if not true.
    assert child.has("set_visible")
    assert child.is_in_group("offer")
    assert child is CanvasItem
    
    # Can also use object labels to imply an interface, i.e. assume it implements certain methods.
    # There are two types, both of which only exist for Nodes: Names and Groups
    
    # Assuming...
    # A "Quest" object exists and 1) that it can "complete" or "fail" and
    # that it will have text available before and after each state...
    
    # 1. Use a name.
    var quest = $Quest
    print(quest.text)
    quest.complete() # or quest.fail()
    print(quest.text) # implied new text content
    
    # 2. Use a group.
    for a_child in get_children():
        if a_child.is_in_group("quest"):
            print(quest.text)
            quest.complete() # or quest.fail()
            print(quest.text) # implied new text content
    
    # Note that these interfaces are project-specific conventions the team
    # defines (which means documentation! But maybe worth it?).
    # Any script that conforms to the documented "interface" of the name/group can fill in for it.
    
    Node child = GetChild(0);
    
    // Dynamic lookup.
    child.Call("SetVisible", false);
    
    // Dynamic lookup, checks for method existence first.
    if (child.HasMethod("SetVisible"))
    {
        child.Call("SetVisible", false);
    }
    
    // Use a group as if it were an "interface", i.e. assume it implements certain methods
    // requires good documentation for the project to keep it reliable (unless you make
    // editor tools to enforce it at editor time.
    // Note, this is generally not as good as using an actual interface in C#,
    // but you can't set C# interfaces from the editor since they are
    // language-level features.
    if (child.IsInGroup("Offer"))
    {
        child.Call("Accept");
        child.Call("Reject");
    }
    
    // Cast check, followed by static lookup.
    CanvasItem ci = GetParent() as CanvasItem;
    if (ci != null)
    {
        ci.SetVisible(false);
    
        // useful when you need to make multiple safe calls to the class
        ci.ShowOnTop = true;
    }
    
    // If one does not wish to fail these checks without notifying users, one
    // can use an assert instead. These will trigger runtime errors
    // immediately if not true.
    Debug.Assert(child.HasMethod("set_visible"));
    Debug.Assert(child.IsInGroup("offer"));
    Debug.Assert(CanvasItem.InstanceHas(child));
    
    // Can also use object labels to imply an interface, i.e. assume it implements certain methods.
    // There are two types, both of which only exist for Nodes: Names and Groups
    
    // Assuming...
    // A "Quest" object exists and 1) that it can "Complete" or "Fail" and
    // that it will have Text available before and after each state...
    
    // 1. Use a name.
    Node quest = GetNode("Quest");
    GD.Print(quest.Get("Text"));
    quest.Call("Complete"); // or "Fail".
    GD.Print(quest.Get("Text")); // Implied new text content.
    
    // 2. Use a group.
    foreach (Node AChild in GetChildren())
    {
        if (AChild.IsInGroup("quest"))
        {
          GD.Print(quest.Get("Text"));
          quest.Call("Complete"); // or "Fail".
          GD.Print(quest.Get("Text")); // Implied new text content.
        }
    }
    
    // Note that these interfaces are project-specific conventions the team
    // defines (which means documentation! But maybe worth it?)..
    // Any script that conforms to the documented "interface" of the
    // name/group can fill in for it. Also note that in C#, these methods
    // will be slower than static accesses with traditional interfaces.
    
  • 将访问权限外包给 FuncRef。在人们需要最大程度地摆脱依赖的情况下,这些方法可能会很有用。在这种情况下,需要依靠外部上下文来设置此方法。

# child.gd
extends Node
var fn = null

func my_method():
    if fn:
        fn.call_func()

# parent.gd
extends Node

onready var child = $Child

func _ready():
    child.fn = funcref(self, "print_me")
    child.my_method()

func print_me():
    print(name)
// Child.cs
public class Child extends Node
{
    public FuncRef FN = null;

    public void MyMethod()
    {
        Debug.Assert(FN != null);
        FN.CallFunc();
    }
}

// Parent.cs
public class Parent extends Node
{
    public Node Child;

    public void _Ready()
    {
        Child = GetNode("Child");
        Child.Set("FN", GD.FuncRef(this, "PrintMe"));
        Child.MyMethod();
    }

    public void PrintMe() {
    {
        GD.Print(GetClass());
    }
}

这些策略有助于Godot的灵活设计。通过它们,用户可以使用多种工具来满足他们的特定需求。