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39 lines
1.4 KiB
Plaintext
39 lines
1.4 KiB
Plaintext
LCL Messages
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This document is for Lazarus developers
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Thumb rules:
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Messages exists for VCL compatibility.
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Messages look like win32 messages, but only those parameters and flags are
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supported, that are commonly used by existing VCL controls (including third
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part controls).
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Every supported flag, that is not commonly used, makes implementing the
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interfaces more difficult. So, think twice, before adding a message.
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Many messages uses hard to read constants and small values (smallint) which
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limits the interfaces and windows does not define the exact ordering of
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messages. Therefore the goal is that every message can be substituted by a
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method. For example: A control can use DoOnChangeBounds instead of WMSize to
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react.
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The LCL should send messages to the interface only in rare cases. In fact, only
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when it is common usage in VCL controls.
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At the moment the interfaces send many messages to the LCL. This amount should
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be reduced in future. Better create a procedure in the LCL, that will send the
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message. This way the parameters are well defined and all interfaces creates
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the messages the same way.
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The messages:
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Interface -> LCL
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WMSize, WMMove - Send from the interface to tell the LCL control to update its
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bounds. Because of the auto aligning/sizing features of the LCL and some
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interfaces, these messages are not sent everytime a HandleObject is resized.
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So, either trust the LCL bounds OR the interface bounds, but don't mix.
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