GoogleMap 本身是可包裹的吗? [英] Is GoogleMap inherently Parcelable?

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

the same thing is working for 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?

for "normal" String, we must create a parcelable class?

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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