QGIS make the appearance of selected feature the same as defined in symbology

Question

I want to select my item one by one in order to capture them separately. I defined their colour like blue and thickness as 1.

According the thread below:

Displaying only selected features on map in QGIS?

I could smoothly define the rule and show only selected elements on my map. However, they appear still as per the default selection settings set in the QGIS options...

I can admittedly change them easily by following the thread here:

Is there anyway to modify thickness & color of a selected polygon?

QGIS 2.8 Change Colour of Selected features

but the problem is, that it's going to be applied for all other items/layers concerned in my project, or even the entire QGIS program.

I would like to keep this changed option only for the layer I am working on right now. Is it possible to change the selection options individually for the layer concerned, or shall I go with the general options as discussed in the threads above?

Answer 1

You can create a virtual layer that will display the selected feature.
This virtual layer should be located above the main layer.

1. Add a virtual field to the point layer, of type integer size 1 and populate it using the expression is_selected()

(note: don't use a boolean type because of this bug.)

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So when a line is selected, the value in this field will be set to 1.

2. Create a virtual layer that will display only the selected line.

Go to the menu Layer > Add Layer > Add/Edit Virtual Layer... and enter the following query. Replace the layer name for yours

select l.*
from lines l 
where  l.selected = 1

3. Style this virtual layer as you wish.

When you select a line, you will have to pan the map a bit to refresh the virtual layer.

4. If you want, you can hide the original selection. In the main layer, in the rule-based symbology, un-tick the box beside the "selected" rule. Doing so will let you apply a thin line style on the selected line.