Can/should I edit the R.java file. If so, how?

问题:

So I'm programming a simple calculator in Eclipse for Android 4.0 and I'm trying to stream-line my code and make it as simple as possible. The place I'm trying to clean up is my findViewById()'s. Since I have buttons 0-9 to instantiate I have a block of code ten lines long that look like this:

b0 = (Button) findViewById(R.id.b0); b1 = (Button) findViewById(R.id.b1); ... b9 = (Button) findViewById(R.id.b9); 

As you can see this thing is just begging for a for-loop. So what I wanted to do was make two arrays. One instance variable array in the Activity which holds all the Button instance variables for the number pad:

private Button[] numberPad = {b0,b1,b2,b3,b4,b5,b6,b7,b8,b9}; 

and then another array in the id class in the R.java file that holds all the button id variables that would look like this:

private static final int[] numberPad = {b0,b1,b2,b3,b4,b5,b6,b7,b8,b9}; 

Sooo that I can reduce ten lines of Button instantiations to two using this loop:

for(int i = 0; i < numberPad.length; i++)     numberPad[i] = (Button) findViewById(R.id.numberPad[i]); 

When I type it out it's fine, but when I go to save it it reverts back automatically to it's original form. I don't see anything wrong with this code. It doesn't produce any errors as far as I can tell. Why can't I edit the R.java file in this way? Is there a way to? Should I?

回答1:

As said before, R file is (or should be) re-generated automatically on every build. You should try some dependency-injection framework (Roboguice works well for Android programming) to clean up issues with handling Views. For example instead of (code taken from project's documentation):

class AndroidWay extends Activity {  TextView name;  ImageView thumbnail;  LocationManager loc;  Drawable icon;  String myName;   public void onCreate(Bundle savedInstanceState) {      super.onCreate(savedInstanceState);      setContentView(R.layout.main);     name      = (TextView) findViewById(R.id.name);      thumbnail = (ImageView) findViewById(R.id.thumbnail);      loc       = (LocationManager) getSystemService(Activity.LOCATION_SERVICE);      icon      = getResources().getDrawable(R.drawable.icon);      myName    = getString(R.string.app_name);      name.setText( "Hello, " + myName );  }}  

You can use simpler and shorter version:

class RoboWay extends RoboActivity {  @InjectView(R.id.name)             TextView name;  @InjectView(R.id.thumbnail)        ImageView thumbnail;  @InjectResource(R.drawable.icon)   Drawable icon;  @InjectResource(R.string.app_name) String myName;  @Inject                            LocationManager loc;   public void onCreate(Bundle savedInstanceState) {      super.onCreate(savedInstanceState);      setContentView(R.layout.main);     name.setText( "Hello, " + myName );  } }  

This not only helps keeping your Views management clean and in-place but is also very helpful when it comes to testing.

回答2:

The R.java file is re-created on every build.

回答3:

As R.java is auto-generated, I think it is a pretty bad idea editing it.

Sometimes when using Eclipse, I get some strange errors concerning R.java, to solve this, I just clean the project, and then every is working again.

Check out this link for more information on resources: http://developer.android.com/guide/topics/resources/accessing-resources.html

回答4:

Even if you did try that approach you will have to use Reflection in order to obtain "findViewbyID" as (R.id.numberPad[i]) will now work without Reflection.

Dont use Reflection either, although it will neaten your code it is very slow.

回答5:

You know, you can implement all that outside the R.java file and in your own classes - just do a static import of R.id.*.

回答6:

R.java is a system generated file which iautomatically generated. You should not try to edit it manually.

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