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<h2>Object Type </h2>
<p>The Object Type view presents the objects on the heap and their position
within it, just as in the <strong>Cell Type</strong> view, but by tagging them
with their C++ type name so that you can easily recognize the objects from your
own code. Determining an object’s type for display is usually possible
for the majority of objects in the heap, but not for them all. An
object’s type can usually be determined if</p>
<ul>
<li>it is an instance of a C++ class with at least one (directly defined or
inherited) virtual function, or</li>
<li>it is a descriptor.</li>
</ul>
<p>If the object type cannot be determined, but there is a unique referrer for
the object type, or if all referrers are of the same known type, <em>[Part of
XXX]</em> is displayed, where XXX is the type of the referrer.</p>
<p>Otherwise, <em>[Unknown]</em> is displayed.</p>
<p>A virtual function in a class means each instance of that class will contain
a vtable pointer. The vtable pointer can be used, in combination with the
symbolic information provided at startup, to determine the name of the class
associated with the vtable for presentation. Symbian’s CBase defines a
virtual destructor, so all conventional C-prefixed classes in Symbian will have
a vtable and so be identifiable in this way.</p>
<p>There are a number of possibilities, but an <em>[Unknown]</em> or <em>[Part
of XXX]</em> object is typically either a raw (non-descriptor) data buffer, or
sometimes a T-class allocated on the heap. Because such an object is often
owned and encapsulated by an identifiable C-class, one effective strategy for
identifying objects, which type cannot be determined, is to use the incoming
reference information Heap Analyser constructs. If an otherwise unknown object
type has this reference information, it is displayed in the view as <em>[Part
of XXX]</em>, where XXX is the type of the referrer. In addition, if you
right-click an <em></em>object and select <strong>Go to…</strong> >
<strong>Incoming reference</strong>, the context menu will display the types of
the objects that refer to the <em></em>object. In fact there are a number of
ways of visualizing object reference relationships available from the
right-click context menu, including drawing the link relationships between
objects as an overlay of dotted lines (right click and select
<strong>Relationships…</strong> > <strong>Incoming</strong> >
<strong>Breadcrumbs</strong>).</p>
<p>Colours are chosen arbitrarily on a type-by-type basis in this view, with
the exception of descriptors (Yellow), <em>[Unknown]</em> and <em>[Part of
XXX]</em> (Red), and free space (Blue). The colour allocation can be viewed and
refined by clicking <strong>Set Filters</strong>. This filter settings panel is
also useful for focusing down on just object types of particular interest;
click <strong>Enable None</strong>, then selectively enable just the types you
are interested in. To get an overview, select <strong>View</strong> >
<strong>Size</strong> > <strong>Small</strong>.</p>
<p><img src="../images/ha_heap_view_object_type.png"></p>
<h5>Related references</h5>
<ul>
<li><a href="cell_type.htm">Cell Type</a></li>
<li><a href="parent_binary.htm">Parent Binary</a></li>
<li><a href="cell_lenght.htm">Cell Lenght</a></li>
<li><a href="isolation.htm">Isolation and Pervasiveness</a></li>
<li><a href="HA_data_analysis.htm">Data analysis with Heap Analyser</a></li>
</ul>
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