how does multiple component with same id work in android?

Question

I have defined several layouts, where few id\'s are multiple defined. I am confused how does it work? why doesn\'t it give error just like we get in java code? and most importan

Answer 1

You can findViewById of the current view hierarchy set to the activity. You cannot have same id for the view's in the same view tree. (must be unique).

Quoting from the docs

Any View object may have an integer ID associated with it, to uniquely identify the View within the tree. When the application is compiled, this ID is referenced as an integer, but the ID is typically assigned in the layout XML file as a string, in the id attribute. This is an XML attribute common to all View objects (defined by the View class) and you will use it very often.

http://developer.android.com/guide/topics/ui/declaring-layout.html

Example

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button myButton = (Button) findViewById(R.id.my_button);
 }

Xml

  <Button android:id="@+id/my_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/my_button_text"/>  

Here

  Button myButton = (Button) findViewById(R.id.my_button);

findViewById is the method R.id.button is an int value. Will have an entry in R.java which is auto generated. Here under the same xml file under the current view tree you cannot have views with same id.

Open your R.java do not modify its content. R.java will look something like below

  public static final class id {
      public static final int my_button=0x7f080004; // this is the int value which is unique
   }

In onCreate you refer like R.id.my_button.

You can have ids same in different xml files because whenever you use findViewById() to get a reference to a part of your layout, the method only looks for that view in the currently inflated layout. (current view tree/hierarchy).

But it is better have ids unique to avoid confusion.

Answer 2

Different View instances can have the same ID. This situation may arise when:

• The instances are inflated from the same xml definition. (Eg.: A custom view has a subview with a given ID. If you use this custom view many times on a layout, the subviews will have the same ID) Custom View which has subviews with same id
• The instances are inflated from different xml files which contain the same ID. two views with same id
• The ID is set by code: setId(42) Android: View.setID(int id) programmatically - how to avoid ID conflicts?

The ID is just a tool what you can use to find Views. It's practically unique in most cases, but not guaranteed.

Answer 3

Using same id for different components in different layouts will not cause any problem. But you cannot use same id for different components in same layout.. Each time a new view is created a unique integer id is assigned to it, which can be found in the R.java file.. But even if we use same id for two components, only one entry is made in to the R.java file. However, it won't cause an error and this works if both components are in different xml layouts. [http://developer.android.com/reference/android/view/View.html][1]

please find the ID section in this page. sorry if this is not what you were looking for