android-custom-views-attributes.md

Title: Android: Custom views and attributes Tags: android|android-custom-views Date: 2013-01-31 11:57:15 -0500 Author: Denevell

First create a class that extends a View, like FrameLayout here. It inflates a normal layout. You can skip that if you extends a TextView or something.

 public class CustomView extends FrameLayout {
 
  public CustomView(Context context) {
    super(context);
  }
 
  public CustomView(Context context, AttributeSet attrs) {
    super(context, attrs);
    LayoutInflater layoutInflator = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View layout = layoutInflator.inflate(R.layout.generic_error_overlay, this);
  }
 
  @Override
  public void onRestoreInstanceState(Parcelable state) {
    if (state instanceof Bundle) {
      Bundle bundle = (Bundle) state;
      // Restore things from bundle here
      super.onRestoreInstanceState(bundle.getParcelable("instanceState"));
      return;
    }
    super.onRestoreInstanceState(state);
  }
 
  @Override
  protected Parcelable onSaveInstanceState() {
    Bundle bundle = new Bundle();
    bundle.putParcelable("instanceState", super.onSaveInstanceState());
    // Add things to bundle here
    return bundle;
  }
 
 }

The onSaveInstanceState / onRestoreInstanceState methods allow you to save the View's state.

To use this in a layout you can do something like:

<your.package.where.the.view.lives.CustomView
 android:layout_width="wrap_content"
 android:layout_height="wrap_content" />

If you want to pass custom attributes, first define the XML namespace in the root element in your layout file:

xmlns:yournamespace="http://schemas.android.com/apk/res-auto" Then you can use a custom attribute in your XML custom view:

<your.package.where.the.view.lives.CustomView
 android:layout_width="wrap_content"
 yournamespace:your_attribute="Hello"
 android:layout_height="wrap_content" />

You then need to define this attribute in attrs.xml. We'll make this one a string.

<resources>
...
 <declare-styleable name="YourAttribute">
     <attr name="your_attribute" format="string"></attr>
 </declare-styleable>
...
</resources>

Then in the constructor for your custom view, you can grab this:

...
TypedArray a = context.getTheme().obtainStyledAttributes(attrs, R.styleable.YourAttribute, 0, 0);
try {
 String string = a.getString(R.styleable.YourAttribute_your_attribute);
} finally {
 a.recycle();
}  	
...

Note we're recycling the TypedArray as it's a shared object. We also refer the the generated styleable attributes in gen that are generated when you added values on attrs.xml.