Hello Gaoming Fu,
I assume that you are receiving this error because you are using standard binaries instead of the NoXAML ones with implicit styles. In such scenario, there simply is no ControlTemplate with such x:Key except if you have defined such by yourself. In order to get familiar with the Implicit Styles
topic, please, check the relevant article from our documentation. You may also find the Difference implicit/non-implicit themes
forum thread useful.
As to the requirement in particular, note, that you do not need to modify the template of GridViewEditorPresenter, as it is responsible for the cell being in edit mode. For styling the selected cell, please, check out the Change RadGridView current cell focus style
forum thread. In addition, you can review the Styling Cells
article from RadGridView's online help.
I hope I've managed to clarify your concern. Feel free to approach me in case further assistance is needed.
Telerik by Progress
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