Книга: Beginning Android

We Attach These to the Java… How?

We Attach These to the Java… How?

Given that you have painstakingly set up the widgets and containers in an XML layout file named main.xml stored in res/layout, all you need is one statement in your activity’s onCreate() callback to use that layout:

setContentView(R.layout.main);

This is the same setContentView() we used earlier, passing it an instance of a View subclass (in that case, a Button). The Android-built view, constructed from our layout, is accessed from that code-generated R class. All of the layouts are accessible under R.layout, keyed by the base name of the layout file — main.xml results in R.layout.main.

To access our identified widgets, use findViewById(), passing in the numeric identifier of the widget in question. That numeric identifier was generated by Android in the R class as R.id.something (where something is the specific widget you are seeking). Those widgets are simply subclasses of View, just like the Button instance we created in Chapter 4.

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