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POJava's lack of template inheritance is causing major code duplication headaches in Android. Any solutions?
 

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  1. POJava's lack of template inheritance is causing major code duplication headaches in Android. Any solutions?
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    <p>This is Android specific.</p> <p>I derive all of my Activities in Android from a custom class that provides a nice, clean place to put common code used by all layouts in the application, especially some common setContentView() override code that injects layouts into my layouts. So here is what a typical hierarchy looks like:</p> <pre><code>MyActivity extends MyBaseClass -&gt; MyBaseClass extends Activity -&gt; Activity </code></pre> <p>For one of my apps, I needed Google Maps support. So I tried to turn MyBaseClass into a template/generic so that I could do something like:</p> <pre><code>MyActivity extends MyBaseClass&lt;MapActivity&gt; -&gt; MyBaseClass&lt;T&gt; extends T -&gt; T </code></pre> <p>Which, of course, failed to compile because Java templates/generics are not nearly as useful as C++ templates as I discovered shortly after the attempt. So I ended up creating a whole separate class as a temporary workaround:</p> <pre><code>MyActivity extends MyBaseMapClass -&gt; MyBaseMapClass extends MapActivity -&gt; MapActivity </code></pre> <p>And copied all the code from MyBaseClass into MyBaseMapClass. The code is identical except for a few minor changes involving imports. It works, but it is hardly a good solution.</p> <p>I crossed my fingers that the above would be the end of the problem and I would never have to revisit it again.</p> <p>Unfortunately, I'm starting to experiment with a fragment and activity mix with a much more complex base class and the problem of code duplication with the above is getting to be a serious issue. Any time I make a change in one file, I have to remember to clone it to the other files and development is moving fast enough that I'm quickly getting out of sync.</p> <p>Activity, MapActivity, FragmentActivity, ListActivity, PreferenceActivity, etc. Do I need to make a separate derived class for each and every one of those that I wish to use? I hope not and, for this reason, I've already limited my derivations to begin with (some of my activities don't have certain features as a result). The problem is further exasperated by the fact I sometimes use two separate base classes (where some activities need to inflate even more views into the layout but not all activities need to do so):</p> <pre><code>MyActivity extends MyBaseClass -&gt; MyBaseClass extends Activity -&gt; Activity MyActivity2 extends AnotherBaseClass -&gt; AnotherBaseClass extends MyBaseClass -&gt; MyBaseClass extends Activity -&gt; Activity </code></pre> <p>If I want to use the code for AnotherBaseClass in Maps, I not only have to create MyBaseMapClass, but also AnotherBaseMapClass and copy the code. I'm up to four classes at this point where two of the classes are a couple thousand lines of cloned code. Replicated code bothers me because it makes maintenance and development that much harder to do.</p> <p>Deriving Android classes introduces complexities such as findViewById() being a part of the Activity base class. That's important because I'm not sure how I would write an interface or composite without running into the same problems I just described.</p> <p>Anyone here encountered this issue and come up with a workable solution?</p>
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    1. USPaula Bean
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    1. CO*"Which, of course, failed to compile"* => Have you tried with `MyBaseClass<T extends Activity>`?
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    2. COThat's why composition should be preferred over inheritance. Side note: are you really Paula Bean? The [Brillant Paula Bean](http://thedailywtf.com/Articles/The_Brillant_Paula_Bean.aspx)?
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    3. CO@assylias - The problem is the use of a reference to "Activity". Yes, I'm pretty sure that is one of the variants I tried. As I mention above, findViewById() is part of Activity among most of the other useful Android SDK calls. I just converted to what you mentioned and I get a lot of errors of the nature of "The method findViewById(int) is undefined for the type MyBaseClass<T>".
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