android2.2-froyo版本底层退出app是怎么实现的

public boolean onKeyDown(int keyCode, KeyEvent event) {

if (keyCode == KeyEvent.KEYCODE_BACK) {

if (getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.ECLAIR) {

event.startTracking();

} else {

onBackPressed();

}

return true;

}

 

 

public boolean onKeyUp(int keyCode, KeyEvent event) {

if (getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.ECLAIR) {

if (keyCode == KeyEvent.KEYCODE_BACK && event.isTracking()

&& !event.isCanceled()) {

onBackPressed();

return true;

}

}

return false;

}