I got solution to this problem.
listeners : {
change : function(field, newValue,o ,e) {
var text = field.value;
if(text.length <= 26 && !text.match(/[.:-]/)) {
if(text.length == 26) {
text = text[25]==' ' ? text : text.substring(0, text.lastIndexOf(' '));
}
var selectedModel = this.up('grid').getSelectionModel().getSelection()[0];
selectedModel.set('Name', text);
}
}
}