java - Android overlay a view ontop of everything?

Question

Can you overlay a view on top of everything in android?

In iPhone I would get the new view set its frame.origin to (0,0) and its width and height to the width and height of self.view. Adding it to self.view would then cause it to act as an overlay, covering the content behind (or if it had a transparent background then showing the view behind).

Is there a similar technique in android? I realise that the views are slightly different (there are three types (or more...) relativelayout, linearlayout and framelayout) but is there any way to just overlay a view on top of everything indiscriminately?

Answer 1

Simply use RelativeLayout or FrameLayout. The last child view will overlay everything else.

Android supports a pattern which Cocoa Touch SDK doesn't: Layout management.
Layout for iPhone means to position everything absolute (besides some strech factors). Layout in android means that children will be placed in relation to eachother.

Example (second EditText will completely cover the first one):

<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/root_view">

    <EditText
        android:layout_width="fill_parent"
        android:id="@+id/editText1"
        android:layout_height="fill_parent">
    </EditText>

    <EditText
        android:layout_width="fill_parent"
        android:id="@+id/editText2"
        android:layout_height="fill_parent">
        <requestFocus></requestFocus>
    </EditText>

</FrameLayout>

FrameLayout is some kind of view stack. Made for special cases.

RelativeLayout is pretty powerful. You can define rules like View A has to align parent layout bottom, View B has to align A bottom to top, etc

Update based on comment

Usually you set the content with setContentView(R.layout.your_layout) in onCreate (it will inflate the layout for you). You can do that manually and call setContentView(inflatedView), there's no difference.

The view itself might be a single view (like TextView) or a complex layout hierarchy (nested layouts, since all layouts are views themselves).

After calling setContentView your activity knows what its content looks like and you can use (FrameLayout) findViewById(R.id.root_view) to retrieve any view int this hierarchy (General pattern (ClassOfTheViewWithThisId) findViewById(R.id.declared_id_of_view)).