Android and general pattern
I recently discovered the following pattern in Android (Intent) classes:
AClass c = data.getParcelableExtra("name");
Signature:
public <T extends Parcelable> T getParcelableExtra(String name)
Further along the path is the actor:
public <T extends Parcelable> T getParcelable(String key) {
unparcel();
Object o = mMap.get(key);
if (o == null) {
return null;
}
try {
return (T) o;
} catch (ClassCastException e) {
typeWarning(key, o, "Parcelable", e);
return null;
}
}
The lack of translation in the getParcelableExtra code call amazed me. I found a structure "like" findViewById (int id). Why is findViewById not implemented with the following signature:
public <T extends View> T genericsFindViewById(int id) {
switch (id){ //Bogus method body as example
case 1:
return (T) new TextView(getActivity());
case 2:
return (T) new RecyclerView(getActivity());
default:
return (T) new ImageView(getActivity());
}
}
//Examples
TextView t = genericsFindViewById(1);
RecyclerView r = genericsFindViewById(2);
ImageView i = genericsFindViewById(4);
TextView t2 = genericsFindViewById(4); // this gives ClassCastException
//But the following would as well:
TextView t3 = (TextView) rootView.findViewById(R.id.image_view);
I have no problem, I just want to understand why they did the casting inside the android structure in one case and not the other?
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This is probably due to historical reasons: these pieces of code are not being written at the same time, not the same factors that are weighed in when choosing a style, etc.
Yesterday at Google I / O 2017 they announced that View.findViewById in Android O api will be declared as public <T extends View> findViewById(int id)
.
As seen here :
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