如何基于当前地图过滤器以及该标记具有的HashMap字符串的组合来设置Google Maps Marker Icon

Question

It would be very helpful if anyone has any suggestions on the most efficient approach for implementing code to set a map marker icon based on:

• Filters defined by the user dictating what markers to display( boolean )
• Keys contained in a HashMap<String, Integer> associated with the marker - in class CrimePoint

Filters Options defined by the user:

    boolean displayAntiSocialBehaviourMarkers;
    boolean displayBurglaryMarkers;
    boolean displayCriminalDamageArsonMarkers;
    boolean displayDrugsMarkers;
    boolean displayOtherTheftMarkers;
    boolean displayPubDisorderWeaponsMarkers;
    boolean displayRobberyMarkers;
    boolean displayShopliftingMarkers;
    boolean displayVehicleCrimeMarkers;
    boolean displayViolentCrimeMarkers;
    boolean displayOtherCrimeMarkers;

Each Marker is created with a CrimePoint which is a class containing all the information necessary to plot a marker

Crime Point Class Variables:

private final Double latitude;
private final Double longitude;
private final String title;

//SNIPPET
//The HashMap storing the categories associated with this CrimePoint.
//Category name is the key and the number of crimes in that category is the Value
//
private Map<String, Integer> crimeCategories;

//An integer to hold the references to the icon image to use
//Example: R.drawable.image002;
private int iconResource;

Marker Icons:

There are 12 different Marker Icons available for the map. One for each filter Option [given above] and a special case marker (Multiple Crimes) where:
- The CrimePoint has more than one Crime Category ( crimeCategories.size() > 1 ) AND
- More than One Crime category contained in the CrimePoint is set to visible using the filter Options

The Marker will only be drawn if there is a (or multiple) crimeCategory that is being shown.

Any help or suggestions would be great as I've spent ages tackling with the logic I need for this and haven't come up with much.

Note: Each time the filter options are changed by the user this function will need to be invoked to change icons on the map and hide/show markers.

Answer 1

First, you should consider changing your representation. Begin with an enumeration of the crime types:

enum CrimeType { AntiSocialBehaviour, ..., Count }

Now your flags can be created as an enum set:

EnumSet<CrimeType> showMarkers = new EnumSet<CrimeType>();

This works like a regular Java Set but is more efficient. Use them within markers rather than a hash if the power of the hash is not needed.

For turning markers on and off, note the visibility attribute in the documentation . When a filter flag is changed, traverse the list of markers setting visibility appropriately. Then invalidate the map fragment or view. The drawing time will dominate the visibility setting time, so this is as efficient as it needs to be.

I am inferring that you have many markers from the question about efficiency. If you have so many markers that the map becomes confused by overlaps, then you must implement a merge algorithm to represent multipler markers with one. I posted this question earlier on this subject and received no response. My solution explained there works quite well, though not as quickly as I'd like (2-3 seconds with about 15,000 markers on a Nexus tablet).

For non-standard marker appearance, study the documentation here under "Change the Default Marker .

It's pretty clear. If you have specific questions and show code, we can help with details.