source: trunk/doc/src/examples/qtscriptcustomclass.qdoc@ 651

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41
42/*!
43 \example script/customclass
44 \title Custom Script Class Example
45
46 The Custom Script Class example shows how to use QScriptClass and QScriptClassPropertyIterator
47 to implement a custom script class.
48
49 The script class we are going to implement is called \c{ByteArray}. It provides a wrapper around
50 the QByteArray class in Qt, with a simplified API. Why do we need such a class? Well, neither the
51 ECMAScript \c{Array} class or \c{String} class is appropriate to use when working with arrays of
52 bytes. Our \c{ByteArray} class will have the right semantics; objects will use only the amount of
53 memory that is really needed (a byte is stored as a byte, not as a floating-point number or a
54 Unicode character) and can be passed directly to C++ slots taking QByteArray arguments (no costly
55 conversion necessary).
56
57 \section1 ByteArray Class In Use
58
59 When the \c{ByteArray} class has been made available to the
60 scripting environment, \c{ByteArray} objects can be constructed like
61 so:
62
63 \snippet doc/src/snippets/code/doc_src_examples_qtscriptcustomclass.qdoc 0
64
65 \c{ByteArray} objects behave similar to normal \c{Array} objects. Every \c{ByteArray} object has
66 a \c{length} property, that holds the length of the array. If a new value is assigned to the \c{length}
67 property, the array is resized. If the array is enlarged, the new bytes are initialized to 0.
68 (This is a difference from normal \c{Array} objects; \c{ByteArray} objects are always dense arrays.)
69 Use normal array operations to read or write bytes in the array. The following code sets all the
70 bytes of an array to a certain value:
71
72 \snippet doc/src/snippets/code/doc_src_examples_qtscriptcustomclass.qdoc 1
73
74 When assigning a value to an array element, the value is truncated to eight bits:
75
76 \snippet doc/src/snippets/code/doc_src_examples_qtscriptcustomclass.qdoc 2
77
78 Like normal \c{Array} objects, if the array index is greater than the current length
79 of the array, the array is resized accordingly:
80
81 \snippet doc/src/snippets/code/doc_src_examples_qtscriptcustomclass.qdoc 3
82
83 Property names that aren't valid array indexes are treated
84 like normal object properties (again, the same is the case for normal \c{Array} objects);
85 in other words, it's perfectly fine to do something like this:
86
87 \snippet doc/src/snippets/code/doc_src_examples_qtscriptcustomclass.qdoc 4
88
89 The above assignment won't affect the contents of the array, but will rather assign a value
90 to the object property named "foo".
91