timer - XNA Simple way to spawn enemys -

im trying spawn enemies list. i've tryed multiple ways in doing so. can't work. there simple way spawn enemes every 3 seconds? edit

i tried spawning this: problem: spawns once

    protected void adjustspawntimes(gametime gametime)     {         // if spawn maximum time > 500 milliseconds,         // decrease spawn time if it's time         // based on spawn-timer variables         if (enemyspawnmaxmilliseconds > 500)         {             timesincelastspawntimechange += gametime.elapsedgametime.milliseconds;             if (timesincelastspawntimechange > nextspawntimechange)             {                 timesincelastspawntimechange -= nextspawntimechange;                 if (enemyspawnmaxmilliseconds > 1000)                 {                     enemyspawnmaxmilliseconds -= 100;                     enemyspawnminmilliseconds -= 100;                 }                 else                 {                     enemyspawnmaxmilliseconds -= 10;                     enemyspawnminmilliseconds -= 10;                 }             }         }     } 

and this: problem: again spawns once

private void spawnenemy()     {         vector2 speed = vector2.zero;         vector2 position = vector2.zero;          // default frame size         point framesize = new point(75, 75);          int screenwidth = graphicsdevice.presentationparameters.backbufferwidth;         int screenheight = graphicsdevice.presentationparameters.backbufferheight;          // randomization:         // - randomly choose side of screen place enemy         // - randomly create position along side of screen         // - randomly choose speed enemy         switch (rand.next(4))         {             case 0: // left right                 position = new vector2(-framesize.x,                                        (rand.next(0, screenheight - framesize.y)));                 speed = new vector2(rand.next(needleminv, needlemaxv),                                     0);                 break;              case 1: // right left                 position = new vector2(screenwidth,                                        (rand.next(0, screenheight - framesize.y)));                 speed = -new vector2(rand.next(needleminv, needlemaxv),                                     0);                 break;              case 2: // bottom top                 position = new vector2(rand.next(0, screenwidth - framesize.x),                                        screenheight);                 speed = -new vector2(0,                                     (rand.next(needleminv, needlemaxv)));                 break;              case 3: // top bottom                 position = new vector2(rand.next(0, screenwidth - framesize.x),                                        -framesize.y);                 speed = new vector2(0,                                    rand.next(needleminv, needlemaxv));                 break;         } 

and 1 spawns not move ive played around updat , draw method nothing seems work

list<enemy> needlelist = new list<enemy>();     texture2d needle;     float spawntime = 10;     const float timer = 10;     bool spawnn = true; 

in update:

    timer = (float)gametime.totalgametime.totalseconds;          spawntime -= (float)gametime.elapsedgametime.totalseconds;         if (timer < 0)         {             foreach (enemy needele in needlelist)             {                 spawnn = !spawnn;                 needele.update(gametime);                 spawntime = timer;             } 

in draw:

    if (spawnn)         {             foreach (enemy needele in needlelist)             {                 needele.draw(gametime, spritebatch);             }         } 

you need break problem steps:

you need global variables represent timer , represent amount of time wait e.g.

float spawntimer; const float time_to_wait = 3.0f; // don't make const if need change. 

next in update need increment time has passed since last update. seem using multiple timers , making more awkward need be. should need multiple timers if you're needing time multiple things.

spawntimer += gametime.elapsedgametime.totalseconds; 

next, when time passed greater amount of time time required wait. spawn enemy , reset timer zero.

if want spawn more 1 enemy @ time, add loop it's condition being loop while iterator less number of enemies spawn.

i've delibrately not given last 2 areas, steps outlined should relatively simple. rest of code should work once done.

if doesn't work, debug code , check if spawnenemy called or not.