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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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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:
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.).
Ensure the operation is performed on the start node:
GET_START_NODE
on the block UI element.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( ).
Review UI element hierarchy:
Make sure you understand the structure of your UI elements and perform operations on the correct nodes.
GET_START_NODE
: Used to retrieve the start node of a block.GET_START_NODE
.If you provide the specific code snippet where the error occurs, I can help you correct it more precisely.
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