Why the soft keyboard shows or not when an activity starts?

Question

When comparing our design between developers, we found a strange behavior. After some analysis we went to this observation.

When the activity starts, on some cases the keyboard appears but sometimes not.

In fact, without a ScrollView, the soft keyboard does not appear by default on an EditText.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".TestActivity" >

    <EditText
        android:id="@+id/editText1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:ems="10"
        android:inputType="text" >
        <requestFocus />
    </EditText>
</LinearLayout>

But when we add a ScrollView, the soft keyboard shows up by default.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".TestActivity" >

    <ScrollView
        android:id="@+id/scrollView1"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1" >
        <EditText
            android:id="@+id/editText1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:ems="10"
            android:inputType="text" >
            <requestFocus />
        </EditText>
    </ScrollView>
</LinearLayout>

It only depends on the presence of the ScrollView. We can fix that with a specific declaration in the AndroidManifest, but this is the default behavior.

I and my fellow developer wonder why is this occurring ?

Answer 1

Here is what I understand of this problem after digging in the code of Android and building some test layouts with an EditText.

As ScrollView is defined as

 public class More ...ScrollView extends FrameLayout { ... }

I tried using a FrameLayout as a container for an EditText item. As a result the software keyboard is not triggered.

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <EditText
        android:id="@+id/editText1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:inputType="text" >
        <requestFocus />
    </EditText>
</FrameLayout>

But as written in the question, using a ScrollView triggers the software keyboard (I simplified the xml source).

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <EditText
        android:id="@+id/editText1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:inputType="text" >
        <requestFocus />
    </EditText>
</ScrollView>

So the element that allows the software keyboard to be triggered is in the ScrollView source file.

Edit: after having created my own class MyFrameLayout extending FrameLayout and playing with the code, I found that it is something in default scrollview style (R.attr.scrollViewStyle) that is responsible for the keyboard to be shown or not...

Edit2: finally the attribute android:scrollbars allows the keyboard to be automatically triggered at startup if present...