Android开发模板------再按一次退出程序 KeyEvent.KEYCODE_BACK

private long mExitTime = 0;
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {

if ((System.currentTimeMillis() - mExitTime) > 2000) {
Toast.makeText(this, "再按一次退出",Toast.LENGTH_SHORT).show();
mExitTime = System.currentTimeMillis();
} else {
MainActivity.this.finish();
}
return true;
}
return super.onKeyDown(keyCode, event);
}