Getting Java.lang.classcastexception: Android.widget.framelayout$layoutparams Cannot Be Cast To Android.widget.relativelayout$layoutparams

Here I need to add textview at runtime. first I took reference of RelativeLayout to get layout params but unfortunately its throwing ClassCastException at RelativeLayout.LayoutPara

Solution 1:

The Error is right and you are also right,but its a misinterpretation on both you and android's part. You see when you Inflate a View with Parent_View being any sub class of a ViewGroup, android returns that View and treat it like a View if you want to treat it like a subclass of a ViewGroup you are going to have some cast Excetpions... You see i know this by experience but i cant give you a documented fact about this

Back to your question; you try to get the Layoutparams of your RelativeLayout which is the top most View of that xml, so i am thinking getLayoutParams() should return null since its not attached to a ViewGroup but its not which means its attached to a FrameLayout which is the Top most View for the Window or itself.

To solve it

try this (1)

instead of using this line

RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)
                          contentLayout.getLayoutParams();

use this

//get the layoutParams of the TextView child in the Relativelayout in //your xml,this will automatically map to the RelativeLayout params
RelativeLayout.LayoutParams params = (android.widget.RelativeLayout.LayoutParams)
                          displayTextView.getLayoutParams();    

or use this(2)

change only your xml, and your previous code will work fine

<RelativeLayout 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"android:paddingLeft="@dimen/activity_horizontal_margin"android:paddingRight="@dimen/activity_horizontal_margin"android:paddingTop="@dimen/activity_vertical_margin"android:paddingBottom="@dimen/activity_vertical_margin"tools:context=".MainActivity">

   <RelativeLayout
      android:id="@+id/content_layout"
      android:layout_width="match_parent"
      android:layout_height="match_parent" >

        <TextView
           android:id="@+id/display_text"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content" />

    </RelativeLayout>
</RelativeLayout>