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132
133
134
135
136<h1>Groups as SubGraphs</h1>
137<p>
138There are some common ways of treating the nodes and links that are the members of a group as if it were its own graph.
139One way to declutter a diagram is to "collapse" a <a>Group</a> to hide the subgraph that it holds.
140</p>
141<p>
142A <a>Group</a> has its own <a>Group.layout</a> that is responsible for the positioning of member <a>Node</a>s
143and the routing of member <a>Link</a>s.
144This is exactly like a <a>Diagram</a> having its own <a>Diagram.layout</a> that positions top-level Nodes and routes top-level Links.
145</p>
146<p>
147Keep in mind that subgraphs are not separate Diagrams and that Groups are just one way of organizing Parts.
148Because subgraphs are collections of Nodes and Links in the same Diagram as the Group itself,
149it is possible to have Links that connect Nodes that are inside a Group with Nodes that are outside of the group.
150It is also possible to have links that connect nodes with the group of which they are a member.
151</p>
152
153<h2 id="LayoutsOfSubgraphs">Layouts of SubGraphs</h2>
154<p>
155You can specify a <a>Layout</a> that applies to a group's subgraph by setting the <a>Group.layout</a> property.
156This operates on the group's member nodes and links as if it were its own diagram.
157A diagram layout of nodes that include groups with their own layout will treat those groups
158as if they were simple nodes, albeit probably larger than normal nodes.
159</p>
160<p>
161In this example the group has a different layout than the layout for the whole diagram.
162In this case the only difference is the direction in which the layout works,
163but you could use a completely different layout algorithm.
164</p>
165<p>
166For simplicity these examples use the default templates for nodes and links.
167</p>
168
169<pre class="lang-js" id="layouts"><code>
diagram.groupTemplate =
  $(go.Group, "Auto",
    // declare the Group.layout:
    { layout: $(go.LayeredDigraphLayout,
                { direction: 0, columnSpacing: 10 }) },
    $(go.Shape, "RoundedRectangle",  // surrounds everything
      { parameter1: 10, fill: "rgba(128,128,128,0.33)" }),
    $(go.Panel, "Vertical",  // position header above the subgraph
      $(go.TextBlock,     // group title near top, next to button
        { font: "Bold 12pt Sans-Serif" },
        new go.Binding("text", "key")),
      $(go.Placeholder,     // represents area for all member parts
        { padding: 5, background: "white" })
    )
  );
185
// declare the Diagram.layout:
diagram.layout = $(go.LayeredDigraphLayout,
                   { direction: 90, layerSpacing: 10, isRealtime: false });
189
var nodeDataArray = [
  { key: "Alpha" },
  { key: "Omega", isGroup: true },
  { key: "Beta", group: "Omega" },
  { key: "Gamma", group: "Omega" },
  { key: "Epsilon", group: "Omega" },
  { key: "Zeta", group: "Omega" },
  { key: "Delta" }
];
var linkDataArray = [
  { from: "Alpha", to: "Omega" }, // from a Node to the Group
  { from: "Beta", to: "Gamma" },  // this link is a member of the Group
  { from: "Beta", to: "Epsilon" },  // this link is a member of the Group
  { from: "Gamma", to: "Zeta" },  // this link is a member of the Group
  { from: "Epsilon", to: "Zeta" },  // this link is a member of the Group
  { from: "Omega", to: "Delta" }  // from the Group to a Node
];
diagram.model = new go.GraphLinksModel(nodeDataArray, linkDataArray);
208</code></pre>
209<script>goCode("layouts", 600, 250)</script>
210
211<p>
212The default layout for a Group is an instance of <a>Layout</a>, just as it is for <a>Diagram</a>.
213So if you do not specify a value for <a>Group.layout</a>, the default layout for the group will position
214all member nodes that do not have a real <a>Part.location</a>.
215</p>
216
217<p>
218If you explicitly set <a>Group.layout</a> to null, the Diagram will be responsible for laying out all of
219Nodes and Links as if the Group did not exist.
220This is possible because a subgraph is not another <a>Diagram</a>.
221</p>
222
223<h2 id="CollapsingAndExpandingGroups">Collapsing and Expanding Groups</h2>
224<p>
225One common technique to visually simplify a diagram is to hide parts of them by "collapsing" them.
226In the case of <a>Group</a>s, it may make sense to be able to hide the subgraph.
227</p>
228<p>
229To collapse a group, set <a>Group.isSubGraphExpanded</a> to false; to make sure it is expanded,
230set that property to true.
231</p>
232<p>
233It is commonplace to provide a button on a group to allow users to collapse and expand groups as they wish.
234<b>GoJS</b> makes this easy to implement by providing a predefined kind of <a>Panel</a>, named "SubGraphExpanderButton",
235that acts as a button to collapse and expand <a>Group</a>s.
236This button changes the visibility of the member nodes and links but does not change
237the visibility of the group itself.
238When the group's visual tree includes a <a>Placeholder</a>, the placeholder will automatically
239shrink when the member parts become invisible and will inflate when the member parts become visible again.
240</p>
241<p>
242Click on the expander button to collapse or expand the group.
243Changing the size of the group also invalidates the layout that is responsible for positioning the group as a single node.
244Often the size of the group changes greatly, so a layout usually needs to be performed again.
245</p>
246<pre class="lang-js" id="collapseExpand"><code>
diagram.groupTemplate =
  $(go.Group, "Auto",
    { layout: $(go.LayeredDigraphLayout,
                { direction: 0, columnSpacing: 10 }) },
    $(go.Shape, "RoundedRectangle", // surrounds everything
      { parameter1: 10, fill: "rgba(128,128,128,0.33)" }),
    $(go.Panel, "Vertical",  // position header above the subgraph
      { defaultAlignment: go.Spot.Left },
      $(go.Panel, "Horizontal",  // the header
        { defaultAlignment: go.Spot.Top },
        $("SubGraphExpanderButton"),  // this Panel acts as a Button
        $(go.TextBlock,     // group title near top, next to button
          { font: "Bold 12pt Sans-Serif" },
          new go.Binding("text", "key"))
      ),
      $(go.Placeholder,     // represents area for all member parts
        { padding: new go.Margin(0, 10), background: "white" })
    )
  );
266
diagram.layout = $(go.LayeredDigraphLayout,
                   { direction: 90, layerSpacing: 10, isRealtime: false });
269
var nodeDataArray = [
  { key: "Alpha" },
  { key: "Omega", isGroup: true },
  { key: "Beta", group: "Omega" },
  { key: "Gamma", group: "Omega" },
  { key: "Epsilon", group: "Omega" },
  { key: "Zeta", group: "Omega" },
  { key: "Delta" }
];
var linkDataArray = [
  { from: "Alpha", to: "Omega" }, // from a Node to the Group
  { from: "Beta", to: "Gamma" },  // this link is a member of the Group
  { from: "Beta", to: "Epsilon" },  // this link is a member of the Group
  { from: "Gamma", to: "Zeta" },  // this link is a member of the Group
  { from: "Epsilon", to: "Zeta" },  // this link is a member of the Group
  { from: "Omega", to: "Delta" }  // from the Group to a Node
];
diagram.model = new go.GraphLinksModel(nodeDataArray, linkDataArray);
288</code></pre>
289<script>goCode("collapseExpand", 600, 250)</script>
290
291<p>
292If you do not want a layout to be performed again when the group changes size,
293you can set the <a>Part.layoutConditions</a> property to control the circumstances under which
294the layout will be invalidated.
295</p>
296
297<p>
<a>Placeholder</a>s can be part of complex panels.
The following example demonstrates a different way to have each Group have a header holding a button and some text.
300</p>
301<pre class="lang-js" id="collapseExpand2"><code>
diagram.groupTemplate =
  $(go.Group, "Auto",
    { layout: $(go.TreeLayout) },
    $(go.Shape, "Rectangle", { fill: "orange", stroke: "darkorange" }),
    $(go.Panel, "Table",
      { margin: 0.5 },  // avoid overlapping border with table contents
      $(go.RowColumnDefinition, { row: 0, background: "white" }),  // header is white
      $("SubGraphExpanderButton", { row: 0, column: 0, margin: 3 }),
      $(go.TextBlock,  // title is centered in header
        { row: 0, column: 1, font: "bold 14px Sans-Serif", stroke: "darkorange",
          textAlign: "center", stretch: go.GraphObject.Horizontal },
        new go.Binding("text")),
      $(go.Placeholder,  // becomes zero-sized when Group.isSubGraphExpanded is false
        { row: 1, columnSpan: 2, padding: 10, alignment: go.Spot.TopLeft },
        new go.Binding("padding", "isSubGraphExpanded",
                       function(exp) { return exp ? 10 : 0; } ).ofObject())
    )
  );
320
diagram.layout = $(go.TreeLayout, { isRealtime: false });
322
diagram.model = new go.GraphLinksModel([
    { key: 1, text: "Alpha" },
    { key: 2, text: "GROUP", isGroup: true },
    { key: 3, text: "Beta", group: 2 },
    { key: 4, text: "Gamma", group: 2 },
    { key: 5, text: "Delta" }
  ], [
    { from: 1, to: 3 },
    { from: 3, to: 4 },
    { from: 1, to: 5 }
  ]);
334</code></pre>
335<script>goCode("collapseExpand2", 600, 200)</script>
336
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