android - 谷歌 map 未在Android中显示标记

我遵循Google Developers网站上给出的所有内容，并将此代码输入MapsActivity.java

package com.pro.soft.inzi.track_trace;

import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.View;
import android.widget.Button;

import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);

        Button sign_in_btn = (Button) findViewById(R.id.b1);
        sign_in_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getApplicationContext(),Live.class);
                startActivity(intent);
            }
        });
        Button history_btn = (Button) findViewById(R.id.b2);
        history_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getApplicationContext(), History.class);
                startActivity(intent);
            }
        });
    }
    @Override
    public void onMapReady(GoogleMap googleMap) {

        // Add a marker in Pakistan and move the camera
        LatLng Pakistan = new LatLng(31, 71);
        googleMap.addMarker(new MarkerOptions().position(Pakistan).title("Marker in Pakistan"));
        googleMap.moveCamera(CameraUpdateFactory.newLatLng(Pakistan));
    }
}

这些是AndroidManifest.xml文件中的权限

<uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES" />
    <!--
 The ACCESS_COARSE/FINE_LOCATION permissions are not required to use
         Google Maps Android API v2, but are recommended.
    -->
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

    <!--
     To retrieve OAuth 2.0 tokens or invalidate tokens to disconnect a user. This disconnect
     option is required to comply with the Google+ Sign-In developer policies
    -->
    <uses-permission android:name="android.permission.USE_CREDENTIALS" />
    <!-- To retrieve the account name (email) as part of sign-in: -->
    <uses-permission android:name="android.permission.GET_ACCOUNTS" />
    <!-- To auto-complete the email text field in the login form with the user's emails -->
    <uses-permission android:name="android.permission.READ_PROFILE" />
    <uses-permission android:name="android.permission.READ_CONTACTS" />

    <permission
        android:name="your.package.name.permission.MAPS_RECEIVE"
        android:protectionLevel="signature" />
    <uses-permission android:name="your.package.name.permission.MAPS_RECEIVE"/>
    <uses-feature
        android:glEsVersion="0x00020000"
        android:required="true"/>

一切正常，除了一个Marker我遵循这个网站的相关问题和网页上的指示，但都是徒劳的。
地图上没有显示标记
请告诉我怎么了。
编辑：这里有activity_maps代码，其中包含MapFragment。

<RelativeLayout
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <Button
        android:id="@+id/b1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/b1_text"
        />
    <Button
        android:id="@+id/b2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/b2_text"
        android:layout_toRightOf="@+id/b1"/>
    <Button android:id="@+id/b3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/b3_text"
        android:layout_toRightOf="@+id/b2"/>

    <RelativeLayout
        android:id="@+id/mainP"
        android:layout_width="match_parent"
        android:layout_height="400dp"
        android:layout_below="@+id/b2">

        <fragment 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:id="@+id/map"
            tools:context=".MapsActivity"
            android:name="com.google.android.gms.maps.MapFragment" />

    </RelativeLayout>
    <EditText
        android:id="@+id/info"
        android:layout_width="160dp"
        android:layout_height="wrap_content"
        android:hint="@string/info_1"
        android:layout_below="@+id/mainP"
        />
    <EditText
        android:layout_width="160dp"
        android:layout_height="wrap_content"
        android:hint="@string/info_2"
        android:layout_below="@+id/mainP"
        android:layout_toRightOf="@+id/info"/>
</RelativeLayout>

最佳答案

首先，您应该在googleMap Object中初始化onCreate(....)

 SupportMapFragment googleMap=(SupportMapFragment)getSupportFragmentManager().findFragmentById(R.id.map);