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How To Fix WD457 - Requested operation is only allowed on the start node of a block


SAP Error Message - Details

  • Message type: E = Error

  • Message class: WD - Workflow definition

  • Message number: 457

  • Message text: Requested operation is only allowed on the start node of a block

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Smart SAP Assistant

  • What is the cause and solution for SAP error message WD457 - Requested operation is only allowed on the start node of a block ?

    Certainly! Here's a detailed explanation of the SAP error message:


    SAP Error Message:

    WD457 - Requested operation is only allowed on the start node of a block


    Cause:

    This error occurs in the Web Dynpro ABAP environment when an operation that is only valid on the start node of a UI element block is attempted on a different node (e.g., a child node or a node that is not the start node).

    In Web Dynpro, UI elements like blocks (containers for UI elements) have a hierarchical structure. Certain operations, such as setting focus, enabling/disabling, or manipulating the block, are only allowed on the start node of that block. If your code tries to perform such an operation on a node that is not the start node, the system raises this error.


    Typical Scenarios:

    • Trying to set the focus on a node that is not the start node of a block.
    • Attempting to enable/disable or make visible/invisible a node that is not the start node.
    • Manipulating UI elements incorrectly in the component controller or view controller.

    Solution:

    1. Identify the node on which the operation is performed:
      Check your code where the operation is executed (e.g., IF_WD_UI_ELEMENT~SET_FOCUS, IF_WD_UI_ELEMENT~SET_ENABLED, etc.).

    2. Ensure the operation is performed on the start node:

      • Use the start node of the block for the operation.
      • You can get the start node of a block by using the method GET_START_NODE on the block UI element.
    3. Example correction:

      DATA: lo_block TYPE REF TO if_wd_ui_element.
      
      lo_block = wd_this->wd_get_api( )->get_element( 'BLOCK_NAME' ).
      
      " Instead of operating on a child node, get the start node
      DATA(lo_start_node) = lo_block->get_start_node( ).
      
      " Perform the operation on the start node
      lo_start_node->set_focus( ).
    4. Review UI element hierarchy:
      Make sure you understand the structure of your UI elements and perform operations on the correct nodes.


    Related Information:

    • Web Dynpro ABAP UI element hierarchy: Understanding the tree structure of UI elements is crucial.
    • Methods like GET_START_NODE: Used to retrieve the start node of a block.
    • SAP Notes and Documentation:
      • Check SAP Help Portal for Web Dynpro ABAP UI element methods.
      • Search for SAP Notes related to WD457 for any patches or updates.

    Summary:

    • Cause: Operation intended only for the start node of a block is attempted on a non-start node.
    • Solution: Use the start node of the block for the operation by retrieving it via GET_START_NODE.
    • Check: UI element hierarchy and ensure correct node usage.

    If you provide the specific code snippet where the error occurs, I can help you correct it more precisely.

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