Replace the if statements, you have to use two equals instead of one. Correct would be
if (AdViewStarted == true) {
adView.destroy();
}
or better
if (AdViewStarted) {
adView.destroy();
}
By the win, variable names are starting with a lowercase char.
Also, what are you trying in your onCreate
?
This is correct (I think, if not, show me the layout xml file and LogCat):
LinearLayout adView = (LinearLayout) findViewById(R.id.adView);
adView.loadAd(new AdRequest());
AdViewStarted = true;