Migrating OpenLaszlo application to 5.0: The tag xxx cannot be used as a child of view - migration

Question

I want to know has anyone across a defect like this when upgrading open laszlo.
The tag xxx cannot be used as a child of view
The tag xxx cannot be used as a child of class
Why this error happens? Any Idea?

Answer 1

The error message xxx cannot be used as a child yyy of view simply means that you are using a tag inside a tag, and the child tag is not known. Simple example:
<canvas debug="true">
<view width="100" height="100" bgcolor="red">
<unknown_tag />
</view>
</canvas>
Compiler error message:
class_tag_error.lzx:4:48: The tag 'unknown_tag' cannot be used as a child of view
class_tag_error.lzx:5:20: Unknown tag
I remember that some people had a similar problem when upgrading from 4.0 to 4.2, here is the discussion in the laszlo-dev mailing list. Is the problem caused by a standard OpenLaszlo tag in your code, or by a custom class or tag you have added?
There is a schema file for all classes and tags the OpenLaszlo compiler knows, which can be found in
$LPS_HOME/WEB-INF/lps/schema/build/lfc.xml
If the compiler complains about a built-in LZX tag, you could - as a last resort - check that file if the class definition for that specific tag still exists in the OpenLaszlo version you are using. Here is - for example - the beginning of the class/interface definition for the <view> tag:
<interface extends="node" jsname="LzView" name="view">
<method args="who, self, prop, refView" name="$lzc$getAttributeRelative_dependencies"/>
<method args="who, self" name="$lzc$getBounds_dependencies"/>
<method args="who, self" name="$lzc$getCurrentTime_dependencies"/>
<method args="ignore" name="$lzc$getMouse_dependencies"/>
<method args="who, self" name="$lzc$getTotalTime_dependencies"/>
<method args="ignore" name="$lzc$isMouseOver_dependencies"/>
... (continued)
Although that's definitely not a comfortable way of finding out if a tag still exists.