来自Google Maps API的Android Studio预览地图不会显示地图

Question

I've created a New project through the wizard, and chosen "Google Maps Activity". Inserted my API key, but there is no map preview, just a gray screen that says . There is also a warning called Unknown fragments that says:

"A <fragment> tag allows a layout file to dynamically include different layouts at runtime. At layout editing time the specific layout to be used is not known. You can choose which layout you would like previewed while editing the layout.
- <fragment com.google.android.gms.maps.SupportMapFragment ...> (Pick Layout...)
 Do not warn about <fragment> tags in this session"

I've been searching in the web for hours and hours, but could not find a way to fix it. If someone can, please let me know, I would really appreciate it.

This is the code from activity_maps.xml

<?xml version="1.0" encoding="utf-8"?> <fragment xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:map="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/map"
    android:name="com.google.android.gms.maps.SupportMapFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MapsActivity"
    tools:layout="@layout/activity_maps" />

And this is the code from MapsActivty.java

>     package com.example.android.myapplication;
>     
>     import android.support.v4.app.FragmentActivity;
>     import android.os.Bundle;
>     
>     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.SupportMapFragment;
>     import com.google.android.gms.maps.model.LatLng;
>     import com.google.android.gms.maps.model.MarkerOptions;
>     
>     public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {
>     
>         private GoogleMap mMap;
>     
>         @Override
>         protected void onCreate(Bundle savedInstanceState) {
>             super.onCreate(savedInstanceState);
>             setContentView(R.layout.activity_maps);
>             // Obtain the SupportMapFragment and get notified when the map is ready to be used.
>             SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
>                     .findFragmentById(R.id.map);
>             mapFragment.getMapAsync(this);
>         }
>     
>         @Override
>         public void onMapReady(GoogleMap googleMap) {
>             mMap = googleMap;
>     
>             // Add a marker in Sydney and move the camera
>             LatLng sydney = new LatLng(-34, 151);
>             mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
>             mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
>         }
>     }

Answer 1

Fragments are not attached to an activity until runtime. Android Studio does not have knowledge of what fragment you're trying to preview. The warning you got says it all. This is not an issue, but rather a limitation of the Android Studio designer.