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docs, document TDbImage OnDbImageRead, OnDbImageWrite, WriteHeader

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jesus 2014-01-24 07:36:42 +00:00
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docs/xml/lcl/dbctrls.xml
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@ -6187,6 +6187,15 @@ Reads flag or writes one to determine if a hint is to be shown when mouse hovers
<element name="TDBCalendar.OnStartDrag" link="#LCL.Controls.TControl.OnStartDrag"/>
<element name="TDBNavigator.BorderSpacing" link="#LCL.Controls.TControl.BorderSpacing"/>
<element name="TDBNavigator.DragCursor" link="#LCL.Controls.TControl.DragCursor"/>
<element name="TDBImage.WriteHeader"><short>Write a header in the image stream.</short><descr><p>The <var>WriteHeader</var> property controls whether or not a header will be written to the image stream. By default a header will be written, this helps to efficiently identify the image format when loading. The writing of a header in the image stream could be a problem if the database will be shared with external applications who do not expect a header in the image stream. In this case, set WriteHeader value to false in order to skip the header writing.
</p><p>The default value is true.</p><p>Note: The <var>WriteHeader</var> value is ignored if <var>OnDbImageWrite</var> event is implemented.
</p>
</descr>
</element><element name="TDBImage.OnDBImageRead"><short>Event to read a custom header from image stream.</short><descr><p>By default, the <var>TDbImage</var> component expect a header at the start of the image stream, this helps to efficiently identify the image format contained in the data stream. On writing, the header is controlled by the <var>WriteHeader</var> property or the <var>OnDbImageWrite</var> event handler. When loading image data which was created by external applications, the data stream may not have a header or the header is not a format identifier that the <var>TDbImage</var> component would recognize.</p><p>The <var>OnDbImageRead</var> event, could be used to identify the image format in the data stream. In the <var>GraphExt</var> parameter it must return a format identifier corresponding to the registered image format. This format identifier could be read from the data stream provided in the <var>s</var> parameter. On return, the data stream should start with the raw image data.</p><p>If the <var>OnDbImageRead</var> handler was not implemented or if it returns an invalid format identifier, the <var>TDbImage</var> component will try to load the image by checking the data stream content. This means that is not necessary to write an <var>OnDbImageRead</var> event handler for the most common image formats, for example: jpg, png, gif or bmp.</p><p>The <var>TDbImage</var> component will be able to indentify the image format even if the data stream doesn't have a header for those TGraphic registered classes that implement the IsStreamFormatSupported method.</p>
</descr>
</element><element name="TDBImage.OnDBImageWrite"><short>Event to write a custom header into image stream.</short><descr><p>Use <var>OnDBImageWrite</var> to write a custom header in the image stream. This header could be "decoded" in the handler for the <var>OnDbImageRead</var> event when loading. The header will be followed by the image raw data.</p><p>By default, <var>TDbImage</var> will write an image header in order to efficiently identify the image format when loading. This behaviour is controlled by the <var>WriteHeader</var> property. If Database will be shared by external applications, it is important to not write an image header. This could be achieved by writing an empty handler for <var>OnDbImageWrite</var>. Note that an empty handler has the same effect than setting <var>WriteHeader</var> to false.</p><p><var>OnDbImageWrite</var> has precedence over the <var>WriteHeader</var> property.</p>
</descr>
</element>
</module>
<!-- DbCtrls -->
</package>