In large saucepan, combine l l/4 cup pineapple juice and sugar. Bring to a boil, and add apples. Cover, and simmer until apples are tender but not soft – 3 to 4 minutes. Lift apples from syrup, and set aside.
Combine cornstarch with remaining 1/4 cup pineapple juice, and add to syrup in pan. Cook, stirring constantly, until thick and bubbly; cook one minute more. Remove pan from heat. Stir butter or margarine, vanilla, and salt into the syrup. Cool 10 minutes without stirring.
Pour about half of the syrup into baked pie shell, spreading it to cover bottom evenly. Arrange cooked apples over syrup in crust. Spoon remaining syrup over apples. Chill.