Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan. Set the pan aside.
In a medium-sized bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, cream together the softened butter and sugar until light and fluffy using an electric mixer or by hand.
Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients in three parts, alternating with the buttermilk in two parts, beginning and ending with the dry ingredients. Mix until just combined, being careful not to overmix.
Gently fold in the crushed pineapple (undrained) and shredded coconut until just combined.
Pour the batter into the prepared baking pan and spread evenly. Bake in the preheated oven for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.
Let the cake cool in the pan for 10-15 minutes before transferring it to a wire rack to cool completely.