Insert to head of ScrollView without shifting

Question

I'm creating a chat application, on launch it displays the twenty most recent messages in a conversation. When you scroll to the top you can press a button to display earlier messages. Pretty typical. The only problem is, I want the UI elements to maintain their position after pressing the button. At the moment they shift. I've created a stripped out version of the problem I'm having.

Before pressing the button

After pressing the button

As you might have guessed, I would like it so that after I press the button the TextView with the label 51 (TextView-51) appears as if it hasn't moved. My original plan was to get the position of TextVie-51 before the button press, and then after the button press, and set the ScrollView's Y position. However that approach doesn't work because the at the time I was checking the View hadn't inflated yet.

Here's the layout xml

<ScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/TestScroller">


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="@dimen/activity_vertical_margin"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin"
        android:id="@+id/mainContainer" >

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/TestButton"
            android:layout_centerHorizontal="true"
            android:layout_alignParentTop="true"
            android:onClick="insertMore"
            android:text="Get Earlier Messages" />
    </RelativeLayout>
</ScrollView>

Here's the code for the activity.

protected void onCreate(Bundle savedInstanceState)
{
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    setContentView(R.layout.test);

    lastId = R.id.TestButton;
    firstId = -1;

    RelativeLayout rl = (RelativeLayout)findViewById(R.id.mainContainer);

    //1. Create fifty TextViews and put them under the button.
    for (int i = 51; i <= 100; i++)
    {
        TextView tv = new TextView(this);
        tv.setText(Integer.toString(i));
        tv.setId(i + 100);

        final int WC = RelativeLayout.LayoutParams.WRAP_CONTENT;
        RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(WC, WC);
        params.addRule(RelativeLayout.BELOW, lastId);

        tv.setLayoutParams(params);

        lastId = tv.getId();

        if (firstId == -1)
            firstId = tv.getId();

        rl.addView(tv);
    }
}

public void insertMore(View view)
{
    //Create fifty more TextViews and insert them between the button and
    //the already created textviews.
    RelativeLayout rl = (RelativeLayout)findViewById(R.id.mainContainer);
    lastId = R.id.TestButton;

    for (int i = 0; i <= 50; i++)
    {
        TextView tv = new TextView(this);
        tv.setText(Integer.toString(i));
        tv.setId(i + 100);

        final int WC = RelativeLayout.LayoutParams.WRAP_CONTENT;
        RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(WC, WC);
        params.addRule(RelativeLayout.BELOW, lastId);

        tv.setLayoutParams(params);

        lastId = tv.getId();
        rl.addView(tv);
    }

    //Now make sure the textview with the label 51 under it is underneath the last
    //view we just added.
    TextView tv = (TextView)findViewById(firstId);
    RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams)tv.getLayoutParams();
    params.addRule(RelativeLayout.BELOW, lastId);
    tv.setLayoutParams(params);

    //Remove the button
    Button button = (Button)findViewById(R.id.TestButton);
    rl.removeView(button);
}

Answer 1

Based on your first idea which was to scroll to the bottom of the list after adding textviews, did you try to call requestLayout() to force layout update :

public void insertMore(View view)
{
// Create and add your 50 views
...

// force Update layout 
rl.requestLayout();

scrollView.post(new Runnable() {
     @Override
     public void run() {
         // Scroll to scrollviews bottom
         scrollView.scrollTo(0, scrollView.getBottom());
     }
});

}