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# OnDeleteBlocks Method of the IZoomViewerEvents Interface

> OnDeleteBlocks method of the IZoomViewerEvents 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 deleting the blocks in [Zoom Viewer](/fine-reader/engine/visual-components-reference/zoomviewer), if this process has been invoked in one of the following ways:

* with the help of the <img src="https://mintcdn.com/abbyy/i-EfCQVmseNiPQcp/images/fine-reader/engine/tb_delblocks.gif?s=df46e9a8cb585622a6ed50468ed4cf17" alt="tb_delBlocks" width="24" height="23" data-path="images/fine-reader/engine/tb_delblocks.gif" /> Delete Block ([MI\_ChooseTool\_DeleteBlock](/fine-reader/engine/visual-components-reference/imageviewer/image-viewer-commands#mi_choosetool_deleteblock)) tool of [Image Viewer](/fine-reader/engine/visual-components-reference/imageviewer)
* by calling MI\_BlockDelete command in Image Viewer or Zoom Viewer

See the [Image Viewer Commands](/fine-reader/engine/visual-components-reference/imageviewer/image-viewer-commands) and [Zoom Viewer Commands](/fine-reader/engine/visual-components-reference/zoomviewer/zoom-viewer-commands) lists to find out how the commands can be called.

## Syntax

### C++

```cpp theme={null}
HRESULT OnDeleteBlocks(
  IIntsCollection* BlocksToDelete,
  VARIANT_BOOL*    Cancel
);
```

### C\#

```csharp theme={null}
void OnDeleteBlocks(
  IIntsCollection BlocksToDelete,
  out bool       Cancel
);
```

### Visual Basic .NET

```vb theme={null}
Sub OnDeleteBlocks( _
  BlocksToDelete As IIntsCollection, _
  ByRef Cancel As Boolean _
)
```

## Parameters

BlocksToDelete

\[in] Contains the indices of blocks that have to be deleted as the [IntsCollection](/fine-reader/engine/api-reference/supplementary-objects-and-methods/intscollection) object.

Cancel

\[out] You may set this variable to TRUE to indicate that the process should be terminated. In this case, the blocks will not be deleted.

## Return values

\[C++ only] If this method returns a value other than S\_OK, it indicates that an error occurred on the client-side, and in this case the value of the Cancel parameter is not taken into account.

## 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

[IZoomViewerEvents](/fine-reader/engine/visual-components-reference/izoomviewerevents)