GoogleMap 本身是可包裹的吗?

问题描述

我对 java 和 android 很陌生.我被一个基本问题困住了.

I am very new to java and android. I am stuck with a basic problem.

在这个给定的 fragment 中，我可以将 GoogleMap 对象添加为 parcelable 而不需要任何额外的 pracelable 类:

In this given fragment, I can add GoogleMap object as parcelable without any extra pracelable class as:

    public class SecondFragment extends Fragment
            implements OnMapReadyCallback {

      public GoogleMap mMap;
      @Override
        public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);                      
          if (savedInstanceState != null) {
            mLastKnownLocation = savedInstanceState.getParcelable(KEY_LOCATION);
            mCameraPosition = savedInstanceState.getParcelable(KEY_CAMERA_POSITION);
          }
        }
 @Override
  public void onSaveInstanceState(Bundle outState) {
    if (mMap != null) {
      outState.putParcelable(KEY_CAMERA_POSITION, mMap.getCameraPosition());
      outState.putParcelable(KEY_LOCATION, mLastKnownLocation);
      super.onSaveInstanceState(outState);
    }
  }

这是我第一次遇到这种可分割的方法，所以，我在另一个类中尝试了相同的字符串:

This is my first encounter with this parcelable approach, so, I tried the same in another class for a string:

public String location;//="No location name found";

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Retrieve location and camera position from saved instance state.
    if (savedInstanceState != null) {
      location = savedInstanceState.getParcelable(KEY_LOCATION_NAME);          
    }
  }

   @Override
  public void onSaveInstanceState(Bundle outState) {
    if (location != null) {
      outState.putParcelable(KEY_LOCATION_NAME, location);
      super.onSaveInstanceState(outState);
    }
  }

这显示编译时间错误:

Error:(205, 49) error: incompatible types: String cannot be converted to Parcelable

所以，我的问题是为什么同样的事情适用于 googleMap 而不是字符串?googleMap 本身是可分块的，对于普通"字符串，我们必须创建一个可分块的类?

So, my question is why the same thing is working for googleMap and not for a string? Is googleMap inherently parcelable, and for "normal" String, we must create a parcelable class?

推荐答案

您可以阅读GoogleMap 类页面以查看它没有 实现 Parcleable.

同样的事情适用于 googleMap

您不是在保存地图...您是在保存 CameraPosition

You are not saving the map... You are saving the CameraPosition

location 是一个字符串，而不是谷歌地图.

location is a String, not a Google Map.

如果您想保存位置，LatLng 或 Location is Parcelable.

对于普通"字符串，我们必须创建一个parcelable类?

没有.对于字符串，只需使用 outState.putString()

Nope. With a string, just use outState.putString()

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