System.ComponentModel.MaskedTextProvider.FindEditPositionFrom C# (CSharp) Method

        public int FindEditPositionFrom(int position, bool direction)
        {
            int startPosition;
            int endPosition;

            if (direction == forward)
            {
                startPosition = position;
                endPosition = _testString.Length - 1;
            }
            else
            {
                startPosition = 0;
                endPosition = position;
            }

            return FindEditPositionInRange(startPosition, endPosition, direction);
        }

        /// <devdoc>
        ///     Overload to allow for passing the text when the mask is being changed from null,
        ///     in this case the maskedTextProvider holds backend info only (not the text).
        /// </devdoc>
        private void SetMaskedTextProvider( MaskedTextProvider newProvider, string textOnInitializingMask )
        {
            Debug.Assert( newProvider != null, "Initializing from a null MaskProvider ref." );
   
            // Set R/W properties.
            newProvider.IncludePrompt    = this.maskedTextProvider.IncludePrompt;
            newProvider.IncludeLiterals  = this.maskedTextProvider.IncludeLiterals;
            newProvider.SkipLiterals     = this.maskedTextProvider.SkipLiterals;
            newProvider.ResetOnPrompt    = this.maskedTextProvider.ResetOnPrompt;
            newProvider.ResetOnSpace     = this.maskedTextProvider.ResetOnSpace;

            // If mask not initialized and not initializing it, the new provider is just a property backend.
            // Change won't have any effect in text.
            if( this.flagState[IS_NULL_MASK] && textOnInitializingMask == null)
            {
                this.maskedTextProvider = newProvider;
                return;
            }

            int testPos = 0;
            bool raiseOnMaskInputRejected = false; // Raise if new provider rejects old text.
            MaskedTextResultHint hint = MaskedTextResultHint.NoEffect;
            MaskedTextProvider oldProvider = this.maskedTextProvider;
            
            // Attempt to add previous text.
            // If the mask is the same, we need to preserve the caret and character positions if the text is added successfully.
            bool preserveCharPos = oldProvider.Mask == newProvider.Mask;

            // Cache text output text before setting the new provider to determine whether we need to raise the TextChanged event.
            string oldText;

            // NOTE: Whenever changing the MTP, the text is lost if any character in the old text violates the new provider's mask.

            if( textOnInitializingMask != null ) // Changing Mask (from null), which is the only RO property that requires passing text.
            {
                oldText  = textOnInitializingMask;
                raiseOnMaskInputRejected = !newProvider.Set( textOnInitializingMask, out testPos, out hint );
            }
            else
            {
                oldText  = TextOutput;

                // We need to attempt to set the input characters one by one in the edit positions so they are not
                // escaped. 
                int assignedCount = oldProvider.AssignedEditPositionCount;
                int srcPos = 0;
                int dstPos = 0;

                while( assignedCount > 0 )
                {
                    srcPos = oldProvider.FindAssignedEditPositionFrom( srcPos, forward );
                    Debug.Assert( srcPos != MaskedTextProvider.InvalidIndex, "InvalidIndex unexpected at this time." );

                    if (preserveCharPos)
                    {
                        dstPos = srcPos;
                    }
                    else
                    {
                        dstPos = newProvider.FindEditPositionFrom(dstPos, forward);

                        if (dstPos == MaskedTextProvider.InvalidIndex)
                        {
                            newProvider.Clear();

                            testPos = newProvider.Length;
                            hint = MaskedTextResultHint.UnavailableEditPosition;
                            break;
                        }
                    }

                    if( !newProvider.Replace( oldProvider[srcPos], dstPos, out testPos, out hint ))
                    {
                        preserveCharPos = false;
                        newProvider.Clear();
                        break;
                    }

                    srcPos++;
                    dstPos++;
                    assignedCount--;
                }

                raiseOnMaskInputRejected = !MaskedTextProvider.GetOperationResultFromHint(hint);
            }


            // Set provider.
            this.maskedTextProvider = newProvider;

            if( this.flagState[IS_NULL_MASK] )
            {
                this.flagState[IS_NULL_MASK] = false;
            }

            // Raising events need to be done only after the new provider has been set so the MTB is in a state where properties 
            // can be queried from event handlers safely.
            if( raiseOnMaskInputRejected )
            {
                OnMaskInputRejected(new MaskInputRejectedEventArgs(testPos, hint));
            }

            if( newProvider.IsPassword )
            {
                // Reset native edit control so the MaskedTextBox will take control over the characters that
                // need to be replaced with the password char (the input text characters).
                // MTB takes over.
                SetEditControlPasswordChar('\0');
            }

            EventArgs e = EventArgs.Empty;

            if (textOnInitializingMask != null /*changing mask from null*/ || oldProvider.Mask != newProvider.Mask)
            {
                OnMaskChanged(e);
            }

            SetWindowText(GetFormattedDisplayString(), oldText != TextOutput, preserveCharPos);
        }