fix ExListView group header collapse-expand button

[NikolayXHD]

Fixes #5427
Fixes #5332 (not clickable part)
Fixes #4886

Has been tested on

• Windows 7

[codecov]

Codecov Report

Merging #5428 into master will decrease coverage by 0.01%.
The diff coverage is 11.76%.

@@            Coverage Diff             @@
##           master    #5428      +/-   ##
==========================================
- Coverage   35.35%   35.33%   -0.02%     
==========================================
  Files         604      605       +1     
  Lines       45977    45996      +19     
  Branches     6273     6279       +6     
==========================================
- Hits        16256    16254       -2     
- Misses      28973    28994      +21     
  Partials      748      748

[gerhardol]

No regression, but not expected:
The button is not visible if width is smaller than the listview size.

[RussKie]

what is this magic "-12" number?

[NikolayXHD]

Well, I was wandering it myself, when I saw it :) Some 15 minutes of googling did not help me find any page with numeric values for nmhrd.code constants.

I will try again, maybe this time I'll have more luck.

-12 was there before the PR, I only moved it to a separate method to make switch-case more compact.

[NikolayXHD]

https://www.pinvoke.net/default.aspx/Constants.NM_

public const int NM_CUSTOMDRAW = NM_FIRST - 12;

[RussKie]

Great, thank you

[RussKie]

[EDIT] retracting the review

[NikolayXHD]

@RussKie I successfully reproduced both issues on current master build.
Just replace click on expand / collapse button by dobule click on group header.

To be more specific:

1. Set truncate long filename setting to None
2. resize file status panel to the size when horizontal scroll appears
3. move scroll to the right (not necessarily rightmost) position
4. [optional] double-click group header twice to collapse and re-expand the group
5. resize the panel in 1 large movement, larger than the missing width created on step 2.

Result: both issues 1, 2 reproduced

Note: step 4 is optional. collapse / expand does not have to do with the issues at all.
The problem is caused by resizing the panel while the scroll is not in leftmost position

[RussKie]

Hmm, I stand corrected, thank you for checking it.
I'll raise new issues.

[RussKie]

Please rebase and I'll get it merged. Thank you

[NikolayXHD]

rebase done