realm-java: java.lang.IllegalStateException: Changing Realm data can only be done from inside a transaction.

10-05 03:44:32.511    1402-1402/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.test.materialup, PID: 1402
    java.lang.IllegalStateException: Changing Realm data can only be done from inside a transaction.
            at io.realm.internal.Table.throwImmutable(Table.java:1474)
            at io.realm.internal.Table.checkImmutable(Table.java:1074)
            at io.realm.internal.UncheckedRow.setString(UncheckedRow.java:207)
            at io.realm.PostRealmProxy.setBody(PostRealmProxy.java:92)
            at com.test.materialup.ui.PostActivity.onClick(PostActivity.java:107)
            at com.test.materialup.adapter.PostRecyclerAdapter$PostViewHolder$1.onClick(PostRecyclerAdapter.java:71)
            at android.view.View.performClick(View.java:4438)
            at android.view.View$PerformClick.run(View.java:18422)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)

While changing a Post object value it gets crashing

 @Override
    public void onClick(int position) {
        Post post = postRecyclerAdapter.getPost(position);
        post.setBody("Hello Wolrd");
    }