Tips & Tidbits

by Steve Sisak

For a program I recently wrote, I wanted to do user input checking for a dialog box as they were typing into an EditText field. I wrote a routine to figure out what the contents of a specific EditText box will be if the current event is allowed to be processed. I then called the routine from my custom dialog event process, and analyzed the results. That way, I could easily decide if the user’s action would produce valid results, or if I needed to abort the current event.

IsDlgControl is a simple check for control characters we always want to process. DivineNewItemString is the routine that does all the work. PStrCopy is a little routine for copying Pascal strings - I’m sure that other people have better ways of doing this.

// some control key constants.
#define kEnterKey3
#define kBackspace 8
#define kTab9
#define kReturnKey 13
#define kEscapeKey 27
#define kLeftKey 28
#define kRightKey29
#define kUpKey   30
#define kDownKey 31
#define kDelete  0xFF

/* IsDlgControl
 * Returns true if c is a special control key (say an arrow key, or escape).
 * Otherwise returns false. */
Boolean IsDlgControl(char c)
{
 if ((c >= kEscapeKey) && (c <= kDownKey)) return true;
 if ((c == kReturnKey) || (c == kEnterKey) || (c == kDelete)
 || (c == kBackspace) || (c == kTab)) return true;
 return false;
 }

/* PStrCpy
 * A little routine to copy Pascal strings. Provided for those people who don’t
 * already use BlockMove() to do this for them ...  */
void PStrCpy(Str255 s, const Str255 t)
{
 short i;

 for (i=0; i<=s[0]; i++) {
 s[i]=t[i];
 }

/* DivineNewItemString
 * Given a DialogPtr, EventPtr and an item number for the active EditText DLOG
 * Item, it returns what the string will be if the current event is processed.
 * It should be called from a custom dialog event proc. */
void DivineNewItemString (DialogPtr d, EventRecord *e, short item, Str255
output)
{
 short  *TEScrpLength = (short *)0x0AB0;
 DialogRecord    *dr;
 TEHandle teh;
 char   c;
 Str255 input, text;
 short  selStart, selEnd;
 short  i;
 short  outStrIdx=0;
 short  iType;
 Handle iHandle;
 Rect   iRect;
    // get the text string
 GetDItem(d,item,&iType,&iHandle,&iRect);
 GetIText(iHandle,text);  // Set the input string
 c = (e->message & charCodeMask);
 if (IsDlgControl(c)) {  
    // if it’s a control char, return the item’s text.
 PStrCpy(output,text);
 return;
 } else if (e->modifiers & cmdKey) {
 if  ((c == ‘v’) || (c == ‘V’)) {
    // if pasting, get the pasted string.
 (void)TEFromScrap();
 HLock(iHandle);
 iHandle = TEScrapHandle();
 for (i=0; i< *TEScrpLength; i++) {
 input[i+1]=((unsigned char *)(*iHandle))[i];
 }
 input[0]=*TEScrpLength;
 HUnlock(iHandle);
 } else { // if any other command stroke ä
 PStrCpy(output,text);
 return;
 }
 } else { // else, set the input string equal to the new character
    // else, set the input string equal to the new character
 input[0]=1;
 input[1]=(unsigned char) c;
 }
    // get the selection point from the TERec
 dr = (DialogRecord *)d;
 teh = dr->textH;
 selStart=(*teh)->selStart;
 selEnd=(*teh)->selEnd;
    // generate output string: copy the first bit of text
 for (i=1; i<=selStart; i++) {
 output[++outStrIdx]=text[i];
 }
    //   copy the input string
 for (i=1; i<=input[0]; i++) {
 output[++outStrIdx]=input[i];
 }
    // copy the last part of text
 for (i=selEnd+1; i<=text[0]; i++) {
 output[++outStrIdx]=text[i];
 } // lastly, set the length
 output[0] = outStrIdx;
 }

Michael Trent