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# OnLongOperationStarted Method of the IImageViewerEvents Interface

> OnLongOperationStarted method of the IImageViewerEvents Interface in ABBYY FineReader Engine Visual Components on Windows — This method is implemented on the client-side.

This method is implemented on the client-side. It is called by ABBYY FineReader Engine before the beginning of a long-term processing operation (e.g., layout analysis, recognition) in [Image Viewer](/fine-reader/engine/visual-components-reference/imageviewer). When the operation is performed, all commands of Image Viewer are disabled and the component is locked. If Image Viewer is connected to Component Synchronizer, all other unlocked synchronized components are locked too.

The method informs the client that a long-term processing operation has been started. You can use this method to block GUI elements of your application during such operations.

## Syntax

### C++

```cpp theme={null}
HRESULT OnLongOperationStarted();
```

### C\#

```csharp theme={null}
void OnLongOperationStarted();
```

### Visual Basic .NET

```vb theme={null}
Sub OnLongOperationStarted()
```

## Return values

This method has no specific return values. It returns the [standard return values of ABBYY FineReader Engine functions](/fine-reader/engine/api-reference/return-codes).

## Remarks

The client implementation of this method must assure that all exceptions thrown inside the method are caught and handled and no exceptions are propagated outside the method. Propagation of an exception outside the method may lead to unpredictable results (such as program termination).

## See also

[IImageViewerEvents](/fine-reader/engine/visual-components-reference/iimageviewerevents)