GOOGLE登入
第八步：宣告

 GoogleSignInClient mgoogleSignInClient;
 int RC_SIGN_IN;

第九步：在程式新增以下代碼(可放在按鈕事件裡)

GoogleSignInOptions gso=new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_GAMES_SIGN_IN)
                .requestEmail()
                .build();
        mgoogleSignInClient = GoogleSignIn.getClient(this,gso);
        Intent signInIntent =mgoogleSignInClient.getSignInIntent();
        startActivityForResult(signInIntent,RC_SIGN_IN);
        ```
第十步：在onActivityResult寫下

if(requestCode==RC_SIGN_IN){
Tasktask=GoogleSignIn.getSignedInAccountFromIntent(data);
handleSignInResult(task);
}
}

第十一步：添加一個funtion

private void handleSignInResult(TaskcompletedTask){
try{
GoogleSignInAccount account=completedTask.getResult(ApiException.class);
} catch (ApiException e) {
e.printStackTrace();
}
}