calculating no of lines when we give text in UITableviewcell?

Question

hi, i want to calculating no of lines when we give text in UITableviewcell?i have inserted text through UITextview which is in UITableview cell.but i want to increase the height of cell based on UItextview which is in UITableview cell.suppose if it has 4 lines ,one height...otherwise other height...i want to also calculate how many lines are in UITextview...and also set height at runtime?any help pls..?

Answer 1

To calculate the approximate size of your UITextView based on a string, try NSString's - (CGSize)sizeWithFont:(UIFont *)font constrainedToSize:(CGSize)size lineBreakMode:(UILineBreakMode)lineBreakMode method.

For example:

NSString *myText = @"Lorem ipsum dolor sit amet, consectetur adipisicing...";

CGSize newSize = [myText sizeWithFont:[textView font]
     constrainedToSize:CGSizeMake([textView frame].size.width, MAXFLOAT)
      lineBreakMode:UILineBreakModeWordWrap];

CGFloat newTextViewHeight = newSize.height;
CGFloat newTableViewCellHeight = newTextViewHeight + 42;

...where textView refers to your UITextView. (I've also assumed that the line break mode of your UITextView is UILineBreakModeWordWrap; if it isn't, make sure you change the appropriate code.)

Answer 2

You can calculate the fitted size of a UILabel based on the NSString content using the UIKitAdditions category on NSString. These methods include...

-sizeWithFont:
-sizeWithFont:constrainedToSize:
-sizeWithFont:constrainedToSize:lineBreakMode:
-sizeWithFont:forWidth:lineBreakMode:
-sizeWithFont:minFontSize:actualFontSize:forWidth:lineBreakMode:

In my implementations of this pattern, I typically use the third one, -sizeWithFont:constrainedToSize:lineBreakMode:.

The most efficient implementations of variable-height UITableViewCells will only calculate the size once per displayed string. This is typically an expensive operation and you definitely don't want expensive operations being performed frequently while scrolling - your scrolling FPS will drop through the floor. This means caching the calculated height somewhere, and for me that somewhere is the model object associated with the specific row.

Personally, I create a custom subclass of UITableViewCell whenever I'm implementing a variable-height table cell. I then create a class method that simply performs the sizeWithFont:constrainedToSize:lineBreakMode: operation given a model object which will contain the string being displayed as a parameter. The table view controller implementation's of tableView:heightForRowAtIndexPath: then looks something like this:

- (CGFloat)tableView:(UITableView*)tableView heightForRowAtIndexPath:(NSIndexPath*)indexPath {
  CGFloat height;
  DataObject *rowData = [self.dataArray objectAtIndex:indexPath.row];

  if (rowData.cachedHeight) {
    height = [rowData.cachedHeight doubleValue];
  } else {
    height = [CustomTableViewCell heightForRowWithString:rowData.contentStr];
    rowData.cachedHeight = [NSNumber numberWithDouble:height];
  }

  return height;
}

N.B. You could/should probably use a UILabel, rather than a UITextView, since you don't need the scrolling behavior of the UITextView.