QT Error: use of undeclared identifier [How to Solve]

When doing some SDK development, we will copy the example code to our own code for testing

In this process, some methods or variables will be copied

The following figure often appears

The system prompts use of unclared identifier ‘a variable’

Generally, this variable may not be defined in the. H file. If you check the header file and find that it is also defined.

However, if this problem still occurs, you need to check and add the class name in front of the method name that reports an error

After the class name is included, no error will be reported

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