如何在 MATLAB 中为对象的属性分配指针？

Question

我想创建一个有限元面向对象的程序。我有一个类 Node。由于有限元网格中的节点（由 Mesh 类表示）是不同的，因此我创建了 Node 类作为值类。当我从类 Node 实例化对象数组时，我将该对象数组分配给 Mesh 的节点属性。我也有一个 Element 类，代表一个有限元。我还从这个类创建了一个对象数组并将其分配给 Mesh 的元素属性。到现在都清楚了。

由于有限元节点也属于元素，我想将一些节点分配给适当的元素。但是复制节点会导致数据冗余，因此我想将指针分配给 Node 对象，以便 Element 的 localNodes 属性包含一个数组指向特定节点的指针。我应该如何修改下面的类来实现它？

节点类：

classdef Node

   properties
      coordinate;
   end

   methods
     % Not interesting for this example
   end

end

元素类：

classdef Element

   properties
      localNodes; % the object instantiated from the class Element
                  % will store an array of pointers to the
                  % appropriate elements of the object array stored
                  % in Mesh.nodes. How can I assign these pointers
                  % to Element.localNodes?
   end

   methods
     % Not interesting for this example
   end

end

Mesh类：

classdef Mesh

   properties
      nodes;    % its object will contain an object array of Node
      elements; % its object will contain an object array of Element
   end

   methods
     % Not interesting for this example
   end

end

Answer 1

最后，在这里进行一些讨论是我将如何解决这个问题的起点：

classdef Node < handle

   properties
      coordinate;
   end

   methods
       function obj=Node(id)
           obj.coordinate=id;
       end
   end

end

.

classdef Mesh < handle

   properties
      nodes;    % its object will contain an object array of Node
      elements; % its object will contain an object array of Element
   end

   methods
       function obj=Mesh(nodes,elements)
           pnodes=cell(1,nodes);
           for idx=1:nodes
               pnodes{idx}=Node(idx);
           end
           obj.nodes=[pnodes{:}];
           pelements=cell(1,numel(elements));
           for idx=1:numel(elements)
               pelements{idx}=Element(obj.nodes(elements{idx}));
           end
           obj.elements=[pelements{:}];
       end
       function non_deleted_nodes=get.nodes(obj)
           %getter to return only not-deleted nodes
           obj.nodes=obj.nodes(arrayfun(@isvalid,(obj.nodes)));
           non_deleted_nodes=obj.nodes;
       end
       function non_deleted_nodes=get.elements(obj)
           %getter to return only not-deleted nodes
           obj.elements=obj.elements(arrayfun(@isvalid,(obj.elements)));
           non_deleted_nodes=obj.elements;
       end

   end

end

.

classdef Element < handle

   properties
      localNodes; % the object instantiated from the class Element
                  % will store an array of pointers to the
                  % appropriate elements of the object array stored
                  % in Mesh.nodes. How can I assign these pointers
                  % to Element.localNodes?
   end

   methods
       function obj=Element(localNodes)
           obj.localNodes=localNodes;
       end
       function non_deleted_nodes=get.localNodes(obj)
           %getter to return only not-deleted nodes
           obj.localNodes=obj.localNodes(arrayfun(@isvalid,(obj.localNodes)));
           non_deleted_nodes=obj.localNodes
       end
       function delete(obj)
           for ix=1:numel(obj.localNodes)
               %The 1 is not a typo, we will delete always the first
               %element until the list is empty
               obj.localNodes(1).delete();
           end
           delete@handle(obj);
       end
   end

end

最后是一个简短的演示：

m=Mesh(10,{[1,2],[2,3],[3,4]})
m.elements(1).localNodes
m.elements(1).localNodes(1).delete()
%now the node is deleted from the element and the mesh
m.elements(2).delete()
%now element 2 together with the nodes is deleted.

Answer 2

您必须使用超类handle，让您使用引用而不是复制数据。

x=MyValueClass(); %assume handle not superclass
y=x; %creates a copy
x=MyHandleClass(); %assume handle is superclass
y=x; %creates a reference to the same instance