Đăng nhập bằng cách liên kết tài khoản google+

Bước 1 : Đầu tiên vào console.developers.google.com tạo mới 1 project

Bước 2 : Vào mục API& auth /APIs enable google+ sign-in

Bước 3 : Vào mục API& auth /Credential nhấp vô tạo mới 1 cái Client ID 
SH1 lấy bằng cách : 
gõ cmd đến đường dẫn sau . . . . 

C:\Program Files\Java\jdk1.7.0_75\bin

rồi gõ 
keytool -exportcert -alias androiddebugkey -keystore%HOMEPATH%/.android/debug.keystore -list -v

pass là : android 

cái đoạn in đậm là đường dẫn của keystore —> nếu chưa có thì down về 
copy cái dòng SHA1

Bước 4 : Code 

Các Bạn Cần Thay đổi những phần sau 
MainActivity + AndroidManifest + UI + Build.gradle 

Build.gradle

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:22.2.1'
    <strong>compile 'com.google.android.gms:play-services:7.5.0'</strong>
}

MainActivity

import android.app.Activity;
import android.content.Intent;
import android.content.IntentSender;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
 
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.Scopes;
import com.google.android.gms.common.SignInButton;
import com.google.android.gms.common.api.CommonStatusCodes;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.ResultCallback;
import com.google.android.gms.common.api.Scope;
import com.google.android.gms.plus.People;
import com.google.android.gms.plus.Plus;
import com.google.android.gms.plus.model.people.Person;
import com.google.android.gms.plus.model.people.PersonBuffer;
 
 
public class MainActivity extends Activity implements
        GoogleApiClient.ConnectionCallbacks,
        GoogleApiClient.OnConnectionFailedListener,
        View.OnClickListener, ResultCallback<People.LoadPeopleResult> {
 
    private String TAG = "MAINACTIVITY" ;
 
    /* Request code used to invoke sign in user interactions. */
    private static final int RC_SIGN_IN = 0;
 
    /* Is there a ConnectionResult resolution in progress? */
    private boolean mIsResolving = false;
 
    /* Should we automatically resolve ConnectionResults when possible? */
    private boolean mShouldResolve = false;
 
 
    /* Client used to interact with Google APIs. */
    private GoogleApiClient mGoogleApiClient;
    private SignInButton mSignInButton;
    private Button mSignOutButton;
    private Button mRevokeButton ;
 
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mSignInButton = (SignInButton) findViewById(R.id.sign_in_button);
        mSignOutButton = (Button) findViewById(R.id.sign_out_button);
        mSignOutButton.setVisibility(View.INVISIBLE); // hide button SignOut
        mRevokeButton = (Button) findViewById(R.id.revoke_button) ;
        mRevokeButton.setVisibility(View.INVISIBLE); // hide button revoke
        // Build GoogleApiClient with access to basic profile
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(Plus.API)
                .addScope(new Scope(Scopes.PROFILE))
                .build();
        mSignInButton.setOnClickListener(this);
        mSignOutButton.setOnClickListener(this);
        mRevokeButton.setOnClickListener(this);
    }
 
    // Invoke GoogleApiClient.connect during Activity.onStart .
 
    @Override
    protected void onStart() {
        super.onStart();
        mGoogleApiClient.connect();
    }
 
    // Invoke GoogleApiClient.disconnect during Activity.onStop .
 
    @Override
    protected void onStop() {
        super.onStop();
        mGoogleApiClient.disconnect();
    }
 
    @Override
    public void onConnected(Bundle bundle) {
        // onConnected indicates that an account was selected on the device, that the selected
        // account has granted any requested permissions to our app and that we were able to
        // establish a service connection to Google Play services.
        Log.d(TAG, "onConnected");
        // Retrieve some profile information to personalize our app for the user.
        Person currentUser = Plus.PeopleApi.getCurrentPerson(mGoogleApiClient);
        Log.e(TAG, "onConnected : " + currentUser.getDisplayName());
        Log.e(TAG, "onConnected : avatar ---> " + currentUser.getImage().getUrl()); // get image
        Log.e(TAG, "onConnected : " + currentUser.getCover().getCoverPhoto().getUrl()); // get image
        Log.e(TAG, "onConnected : " + currentUser.getUrl());
        String email = Plus.AccountApi.getAccountName(mGoogleApiClient); // getemail
        Log.e(TAG, "onConnected : " + email);
        mShouldResolve = false;
 
        // Show the signed-in UI
        showSignedInUI();
 
    }
 
    private void showSignedInUI() {
        mSignInButton.setVisibility(View.INVISIBLE);
        mSignOutButton.setVisibility(View.VISIBLE);
        mRevokeButton.setVisibility(View.VISIBLE);
 
        Plus.PeopleApi.loadVisible(mGoogleApiClient, null)
                .setResultCallback(this);
    }
 
    @Override
    public void onConnectionSuspended(int i) {
 
    }
 
    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.sign_in_button) {
            onSignInClicked();
        }
        else if(v.getId() ==  R.id.sign_out_button){
            onSignOutClicked() ;
        }
        else {
            onRevokeClicked() ;
        }
 
    }
 
    private void onRevokeClicked() {
        // After we revoke permissions for the user with a GoogleApiClient
        // instance, we must discard it and create a new one.
 
        if (mGoogleApiClient.isConnected()) {
            Plus.AccountApi.clearDefaultAccount(mGoogleApiClient);
            Plus.AccountApi.revokeAccessAndDisconnect(mGoogleApiClient);
            mGoogleApiClient.disconnect();
        }
        showSignedOutUI();
    }
 
 
    private void onSignOutClicked() {
        if (mGoogleApiClient.isConnected()) {
            Plus.AccountApi.clearDefaultAccount(mGoogleApiClient);
            mGoogleApiClient.disconnect();
            showSignedOutUI();
        }
    }
 
    private void onSignInClicked() {
        // User clicked the sign-in button, so begin the sign-in process and automatically
        // attempt to resolve any errors that occur.
 
        mShouldResolve = true;
        mGoogleApiClient.connect();
    }
 
    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {
        // Could not connect to Google Play Services.  The user needs to select an account,
        // grant permissions or resolve an error in order to sign in. Refer to the javadoc for
        // ConnectionResult to see possible error codes.
        Log.d(TAG, "onConnectionFailed:" + connectionResult);
 
        if (!mIsResolving && mShouldResolve) {
            if (connectionResult.hasResolution()) {
                try {
                    connectionResult.startResolutionForResult(this, RC_SIGN_IN);
                    mIsResolving = true;
                } catch (IntentSender.SendIntentException e) {
                    Log.e(TAG, "Could not resolve ConnectionResult.", e);
                    mIsResolving = false;
                    mGoogleApiClient.connect();
                }
            } else {
                // Could not resolve the connection result, show the user an
                // error dialog.
                showErrorDialog(connectionResult);
            }
        } else {
            // Show the signed-out UI
            showSignedOutUI();
        }
 
    }
 
    private void showErrorDialog(ConnectionResult connectionResult) {
 
    }
 
    private void showSignedOutUI() {
        mSignInButton.setVisibility(View.VISIBLE);
        mSignOutButton.setVisibility(View.INVISIBLE);
        mRevokeButton.setVisibility(View.INVISIBLE);
    }
 
    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        Log.d(TAG, "onActivityResult:" + requestCode + ":" + resultCode + ":" + data);
 
        if (requestCode == RC_SIGN_IN) {
            // If the error resolution was not successful we should not resolve further.
            if (resultCode != RESULT_OK) {
                mShouldResolve = false;
            }
            mIsResolving = false;
            mGoogleApiClient.connect();
        }
    }
 
 
    @Override
    public void onResult(People.LoadPeopleResult loadPeopleResult) {
        if (loadPeopleResult.getStatus().getStatusCode() == CommonStatusCodes.SUCCESS) {
 
            PersonBuffer personBuffer = loadPeopleResult.getPersonBuffer();
            try {
                int count = personBuffer.getCount();
                for (int i = 0; i < count; i++) {
                    Log.e("TAG","onResult : "+personBuffer.get(i).getDisplayName()) ;
                }
            } finally {
                personBuffer.close();
            }
        } else {
            Log.e(TAG, "onResult ---> Error requesting visible circles: " + loadPeopleResult.getStatus());
        }
    }
}

AndroidManifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.boxopens.login" >
    &lt;uses-permission<strong> android:name="android.permission.INTERNET" /&gt;
   </strong> &lt;uses-permission<strong> android:name="android.permission.GET_ACCOUNTS" /&gt;
   </strong> &lt;uses-permission<strong> android:name="android.permission.USE_CREDENTIALS" /&gt;</strong>
    &lt;application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"&gt;
        &lt;activity
            android:name=".MainActivity"
            android:label="@string/app_name" &gt;
            &lt;intent-filter&gt;
                &lt;action android:name="android.intent.action.MAIN" /&gt;
 
                &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
            &lt;/intent-filter&gt;
        &lt;/activity&gt;
        &lt;meta-data
            android:name="com.google.android.gms.version"
            android:value="@integer/google_play_services_version" /&gt;
    &lt;/application&gt;
 
&lt;/manifest&gt;

UI

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
 
    <com.google.android.gms.common.SignInButton
        android:id="@+id/sign_in_button"
        android:layout_width="match_parent"
        android:foregroundGravity="center"
        android:layout_height="wrap_content" />
 
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Sign-out"
 
            android:id="@+id/sign_out_button" />
 
        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Revoke"
            android:id="@+id/revoke_button"/>
    </LinearLayout>
 
 
</RelativeLayout>