Hi everyone
I am struggling a little bit with the concept of deferred binding and/or
dependency injection in libraries/widgets.
I try to come up with the best approach for following problem:
I implemented a visualization widget (composite) that takes in some data and
displays it.
I want to separate the way the data is retrieved from the actual
visualization part. So I added a generic interface "DataSource" which looks
like this:
public interface DataSource {
public void fetch(int start, int end, boolean getFeatures,
GeneomeDataSourceCallback callback);
}
and I add a setter to my Widget: public void setDataSource(DataSource
source) { this.source = source}
In oder to support http like datasources I also added an abstract class
which implements the DataSource Interface and takes an URL in its default
constructor:
public abstract class HttpDataSource implements DataSource {
protected String url;
public HttpDataSource(String url) {
this.url = url;
}
}
My specific DataSouce extends this abstract class and implements the fetch
method of the interface:
public class MyDataSource extends HttpDataSource {
public MyDataSource(String url) {
super(url);
}
}
This works well. I can create an instance of the MyDataSource class pass it
to the setter of my widget.
Now I want to make the widget somewhat configurable. I know that this can be
done by either Dependency Injection or Deferred Bindings.
So one approach would be to allow the user of the widget to set the
DataSource in the Module XML file (similar to the way it is done in the
gwt-log library:
http://code.google.com/p/gwt-log/source/browse/trunk/Log/src/com/allen_sauer/gwt/log/gwt-log-impl.gwt.xml
)
<replace-with class="MyDataSource">
<when-type-is class="DataSource" />
<when-property-is name="source" value="MyDataSourceName" />
</replace-with>
However I don't know if that is possible because by passing a url into the
constructor of MyDataSource I have a state and I am not sure how this works
with deferred binding.
On a side note: would it be possible to have the url also configured in the
module's XML file?
I am also worried if people who use this widget/library can implement their
own DataSource and pass it to the widget (doesn't it interfere with the
deferred binding?)
I suppose another solution would be using dependency injection in the parent
application which uses the visualization widget/library ( how can the url be
passed, etc? I probably have to inject a Factory?)
Which one of these two solutions is better and in general does it make sense
to use deferred binding or GIN to solve this problem?
thanks in advance
Uemit
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