Godot 接口

我们常常需要依赖其他对象来获取功能的脚本。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。

本教程接下来的部分将介绍各种完成这些操作的方法。

获取对象引用

对所有 Object 来说，获得引用的最基础的方法，是从另一个已获得引用的对象来获得。

GDScriptC#

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。虽然使用者经常以这种方式访问 Node 和 Resource，但还有另一种方法。

除了访问属性和方法，也可以通过加载来获得 Resource。

GDScriptC#

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
{
    // 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. 在一种语言中，有许多加载这些资源的方法。

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.

GDScriptC#

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.
    # Note: Scripts run from a release export template don't
    # run `assert` statements.
    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.
func reference_a_global_autoloaded_variable():
    print(globals)
    print(globals.prop)
    print(globals.my_getter())

public class MyNode
{
    // Slow
    public void DynamicLookupWithDynamicNodePath()
    {
        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 LookupAndCacheForFutureAccess()
    {
        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 setter 和 getter 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 setter 或 getter. 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 script 或 meta 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 TileSet 的 1/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.

  GDScriptC#

  # 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_visible 和 is_visible .

  GDScriptC#

  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_method("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_method("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 or
  # 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 or 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.

GDScriptC#

# 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 : Node
{
    public FuncRef FN = null;
    public void MyMethod()
    {
        Debug.Assert(FN != null);
        FN.CallFunc();
    }
}
// Parent.cs
public class Parent : 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.