That's a solution that would work, but the average user should not have to jump through hoops just to install a plug-in. Force quiting processes in any OS can have dangerous and unintended consequences and should not be attempted, unless you know what you are doing.
I have installed countless Flash updates over the years, and this is the first time this has happened. So, if I've been running the "dashboardclient" for years, this tells me Adobe dropped the ball on this installer.
Bottom line: The end-user should have an installer that doesn't require monkeying around with user processes. If a process has to be stopped, most installers will require a restart and take care of it through the installer. Many others do this, Adobe should as well.
(P.S.: Deleting the "Flash Player.plugin" (HD>Library>Internet Plug-Ins) will allow for an install, without quitting the Dashboard processes,)
The "average user" of OS 10.7, 10.8 or 10.9 better get used to it, because they operate differently than anything before Lion.
Gatekeeper, and "iOS like" apps have changed the face of OS X permanently. Social media plug-ins, that stay connected even when a browser is closed, will cause problems when they also use browser plug-ins like Flash Player.
I've also been a Windows user since 1998 and it's just as bad, if not worse. You can't install ANYTHING that a browser uses until it's closed and Internet Exploder will often stay open after it appears closed, so it must be terminated manually before a plug-in can be installed or updated.
And... trashing the Flash Player.plugin (& emptying the trash) will force terminate the dashboard widget that was using it, which is what allows the install without having to go to Activity Monitor.
Actually, I install programs all the time, and NONE of them force me to MANUALLY close a user process.
The average user IS NOT, nor does he want to be, technically savvy. He wants to USE the computer. He wants to watch YouTube videos, not monkey around with the system.
It's really simple. If an installer needs to quit a process, or modify a file that is in use, it simply writes those properly and gets rid of the old one after a restart. Windows is the same way. Adobe dropped the ball on this installer and they should fix it.
Finally, moving the "Flash Player.plugin" (HD>Library>Internet Plug-Ins) to the trash DOES allow the installer to complete WITHOUT stopping the dashboardclient processes. You can empty the trash after a restart (getting rid of that old file, --much like a properly-written installer would do).
GREAT answer, ShawnBurbank!
thank you thank you thank you! I have been unsuccessfully trying to install the flash player for more than a month and simply deleting that one plug in did it!!!!
you've saved me unknown hours of frustration.