Question

Rather than using Bean model objects, my data model is built on Key-Value pairs in a HashMap container.

Does anyone have an example of the GXT’s Grid ValueProvider and PropertyAccess that will work with a underlying Map?

Answer 1

It doesn’t have one built in, but it is easy to build your own. Check out this blog post for a similar way of thinking, especially the ValueProvider section: http://www.sencha.com/blog/building-gxt-charts

The purpose of a ValueProvider is to be a simple reflection-like mechanism to read and write values in some object. The purpose of PropertyAccess<T> then is to autogenerate some of these value/modelkey/label provider instances based on getters and setters as are found on Java Beans, a very common use case. It doesn’t have much more complexity than that, it is just a way to simply ask the compiler to do some very easy boilerplate code for you.

As that blog post shows, you can very easily build a ValueProvider just by implementing the interface. Here’s a quick example of how you could make one that reads a Map<String, Object>. When you create each instance, you tell it which key are you working off of, and the type of data it should find when it reads out that value:

public class MapValueProvider<T> implements 
            ValueProvider<Map<String, Object>, T> {
    private final String key;
    public MapValueProvider(String key) {
        this.key = key;
    }

    public T getValue(Map<String, Object> object) {
        return (T) object.get(key);
    }
    public void setValue(Map<String, Object> object, T value) {
        object.put(key, value);
    }

    public String getPath() {
        return key;
    }
}

You then build one of these for each key you want to read out, and can pass it along to ColumnConfig instances or whatever else might be expecting them.

The main point though is that ValueProvider is just an interface, and can be implemented any way you like.