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| -rw-r--r-- | doc/src/qmlapp/performance.qdoc | 46 |
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diff --git a/doc/src/qmlapp/performance.qdoc b/doc/src/qmlapp/performance.qdoc index 91952770..19bb0c9e 100644 --- a/doc/src/qmlapp/performance.qdoc +++ b/doc/src/qmlapp/performance.qdoc @@ -80,52 +80,6 @@ such as those done to the bindings compiler, it can (in some use-cases) be faste than calling a C++ function. However, care must be taken to ensure that unnecessary processing isn't triggered accidentally. -\section2 Bindings - -There are two types of bindings in QML: optimized and non-optimized bindings. -It is a good idea to keep binding expressions as simple as possible, since the -QML engine makes use of an optimized binding expression evaluator which can -evaluate simple binding expressions without needing to switch into a full -JavaScript execution environment. These optimized bindings are evaluated far -more efficiently than more complex (non-optimized) bindings. The basic -requirement for optimization of bindings is that the type information of every -symbol accessed must be known at compile time. - -Things to avoid in binding expressions to maximize optimizability: -\list - \li declaring intermediate JavaScript variables - \li accessing "var" properties - \li calling JavaScript functions - \li constructing closures or defining functions within the binding expression - \li accessing properties outside of the immediate evaluation scope - \li writing to other properties as side effects -\endlist - -Bindings are quickest when they know the type of objects and properties they are working -with. This means that non-final property lookup in a binding expression can be slower -in some cases, where it is possible that the type of the property being looked up has -been changed (for example, by a derived type). - -The immediate evaluation scope can be summarized by saying that it contains: -\list - \li the properties of the expression scope object (for binding expressions, this is - the object to which the property binding belongs) - \li ids of any objects in the component - \li the properties of the root item in the component -\endlist - -Ids of objects from other components and properties of any such objects, as -well as symbols defined in or included from a JavaScript import, are not in the -immediate evaluation scope, and thus bindings which access any of those things -will not be optimized. - -Note that if a binding cannot be optimized by the QML engine's optimized binding -expression evaluator, and thus must be evaluated by the full JavaScript environment, -some of the tips listed above will no longer apply. For example, it can sometimes be -beneficial to cache the result of property resolution in an intermediate JavaScript -variable in a very complex binding. Upcoming sections have more information on these -sorts of optimizations. - \section2 Type-Conversion One major cost of using JavaScript is that in most cases when a property from a QML |