I'm having trouble understanding the action economy of joining "melee combat" with "spellcasting".
Jon is a Hexblade warlock (Xanathar's Guide to Everything, p. 55) that likes using his Pact of the Blade Greatsword, or, if feeling down, a Pact of the Blade Rapier and a Shield. Basically, he's either going two-handed-mode, or sword-and-board. Jon, in his great sapience, took some useful spells, such as blur, and the War Caster feat to get advantage on his Concentration saves and also eliminate the need for a free hand on spells with somatic components.
However, this is not enough for Jon. He also took hypnotic pattern, which Jon believes to be borderline OP. However, hypnotic pattern has both material and somatic components, so Jon can't just whiff out spells through his weapon. So, how can Jon alternate between casting and attacking without dropping his awesome weapon on the ground for others to steal?
Jon thinks he should start by using a component pouch to avoid having to waste "free object interactions" to get his material components (as seen here). He thinks it might be possible, when in 2h-mode, to release one hand, cast whatever, grab weapon again.
He's not sure it is possible, in 1h+shield mode, to drop the weapon, cast the spell, and pick it back up. Is Jon correct?
Best Answer
It's possible, but Kludgy.
When going Sword and Board, Jon has no free hands, and no easy opportunity for a free hand, to access their Component Pouch or Focus. The only way to access a material component would be to drop their weapon, access the Material Component, and then pick the weapon back up.
This is possible, as dropping an item has no interaction cost, it can just happen. That leaves Jon with the Object Interaction to pick up the blade after he casts his spell requiring the material component.
When going two-handed weapon, Jon can simply release a hand, cast, and grab ahold again. No cost penalty there.
Do also note that it costs a full action to Don/Doff a shield (in case Jon isn't sure if they're going to go into battle sword/board or two-handed...he probably needs to have made up his mind earlier.)
Beware of the Readied Action
If this becomes a known tactic of Jon, there may be an enemy out there at some time who waits for this opportunity and snatches up the weapon using a Readied Action triggered off it dropping (and therefore not giving Jon a chance to pick it back up.)
Worst case scenario here is that Jon uses his action next turn to create a new pact weapon.