Ive checked the message boards and have come across people curious about spell storing weapon enchant, and thrown weapons. The enchant allows for the spell to go off if the wielder so wishes, however if you throw the weapon you are no longer wielding it. This I agree with. Now the thing I want to know about this is if you added String/Twine to a dagger would you still be wielding it after its thrown in the same way you would still be able to be touching your weapon if you had a weapon cord, but a weapon cord is not long enough for this idea.
TL;DR
Can a thrown weapon with string/twine attached to a player still trigger spell storing enchants, IF NOT how would one make a thrown weapon be trapped/explode?
String or Twine: Sold in balls or spools of 50 feet, string and twine are useful for rigging traps and alarms and are a vital component of grappling bolts and arrows. String or twine has hardness 0, 1 hit point, and Break DC 14.
Spell Storing is melee-only. It says so at the end of a description. Any weapon, even with the Thrown quality or Throwing enchancement or other similar ability, is not considered "Melee" the moment it's launched - it becomes "Ranged" then - so Spell Storing doesn't function with it.
Even if you take a Longsword and throw it with the Throw Anything feat, you're still making a Ranged attack, so effects that are only applicable for Melee no longer work with it.
Even if you have a string attached to it, it's still a Thrown weapon. What you described is an improvised Rope Dart; Rope Darts are Ranged, even though there may be some feats which allow you to use it in Melee (since you twirl it before launching it).
If you want to hit someone far away and still be in Melee, I'd suggest being a Titan Mauler Barbarian and use a Large Spiked Chain with Spell Storing then.
There should be other ways to do it as well, but these were off the top of my head.
Arguably, your DM could allow you to create Throwing Daggers charged with a single CL5 Fireball (5d6 fire) for 750gp; the Dagger would be thrown, where it lands would be the radial point for the Fireball, and once used, the spell would be completely discharged and the Dagger destroyed.
While you could spam these and do ridiculous amounts of damage in one round of combat, you'd also be wasting close to 800gp per dagger, and you can only craft 1 dagger a day.
At that point, playing an Alchemist is more efficient, since they get scaling Bombs, for free, several times a day. So your DM may well allow it, though I don't suggest it myself.
A Spell Storing weapon has to hit and do damage to a creature for the spell to go off.
Spell Storing: A spell storing weapon allows a spellcaster to store a single targeted spell of up to 3rd level in the weapon. (The spell must have a casting time of 1 standard action.) Anytime the weapon strikes a creature and the creature takes damage from it, the weapon can immediately cast the spell on that creature as a free action if the wielder desires. (This special ability is an exception to the general rule that casting a spell from an item takes at least as long as casting that spell normally.) Once the spell has been cast from the weapon, a spellcaster can cast any other targeted spell of up to 3rd level into it. The weapon magically imparts to the wielder the name of the spell currently stored within it. A randomly rolled spell storing weapon has a 50% chance to have a spell stored in it already.
By a strict reading, just throwing a dagger and having it explode doesn't work. That said, I also can't find a strict reading that says the weapon has to be in-hand when it hits a creature. Seems reasonable enough to me to allow a thrown weapon to activate as long as it hits a creature and does damage. This may be a table variation rule though.
Edit: I would rule that the call to release the spell has to be made before the weapon leaves the thrower's hand. If it doesn't hit/do damage the spell stays in the weapon.
In the idea of creating the throwing weapons charged with single spells, to create that, it gives the formula as Spell Level X Caster level X 50gp, however its listed as a "potion". With this idea would it be more of a Craft Magic Arms and Armor? Im assuming so as its a weapon this is applying to. Also would the weapons be destroyed on the "explosion" of a fireball going off from say a star knife?