Single Engine Pilot reported failing to execute SOP's. The pilot reported accidentally turning off main power and unable to extend the gear completely. The aircraft landed and the partially extended gear collapsed. No injuries were reported.

Narrative

I was inbound to ZZZ and just prior to entering the 45 to Runway XX at 2;200 FT MSL. This is where I normally do GUMP #1 of 2; which was apparently interrupted by inadvertently tripping the main switch; which is located right in front of the fuel pump switch. Once I was on the ground I realized that this mistake was a crucial contributing factor. I saw that the gear level had been activated and the main switch was in the off position. All instruments went dark including all radios; indicator lights; etc. In the confusion I assumed I had gotten the gear down just prior to the power event and focused my attention to getting on the ground quickly and safely as possible. I turned base short final off of the downwind; high and fast as 40 degree flaps were unavailable due to the power issue. I held it off as long as possible to slow the aircraft taking advantage of the amount of runway (6;500 FT) I had available. Upon touchdown I thought I had blown a tire; however it was apparently the landing gears collapsing beneath me. Upon lifting the plane from the runway; it appeared like they were partially deployed however they didn't get locked in which resulted in the gear up landing. Replaying this scenario in my head over and over had made me more aware of this exact type of situation. Having experienced this incident in real time and now knowing what I should have done in this type of situation to avoid this type of landing will definitely make me a better situational pilot for the future. A practical lesson in losing electrical systems would have prepared me to identify and perform in an effective methodical manner which I now know would have avoided the final result of this incident. In hindsight; with plenty of fuel and good magnetos; I had plenty of time to perform the necessary procedures in order to resolve the situation and successfully avoid this incident.