UILabel Refresh

问题

I have looked into this, but I’m still not quite clear how to do it. I have a UILabel. I would like to write out a word... letter by latter. It goes through each letter, then at the end the entire word shows up. At first I thought it was just because it was too fast, so I put in a delay with something like this.

    typedWord.text = [typedWord.text stringByAppendingString:@"C"];
    future = [NSDate dateWithTimeIntervalSinceNow: letterPause ];
    [NSThread sleepUntilDate:future];

Then I read that it may be because it doesn’t refresh until the function call is finished. The suggestion was to use a selector call. I’m not sure how to do this. Any suggestions?

回答1:

You are sleeping the main thread, so the UI is not getting refreshed until the end of the sleep.

You need to implement something like the following:

// This code is in your view controller somewhere, where you initially decide to update the label. typedWord is the outlet to your UILabel.
NSString *newText = @"Hello";
typedWord.text = @"";
[self performSelector:@selector(updateLabel:) withObject:newText afterDelay:0.2];

This calls:

// This is a separate method in your view controller, so typedWord still refers to the label outlet.
-(void)updateLabel:(NSString*)newText 
{
    // Get the first character of the passed in string
    NSString *firstCharacter = [newText substringToIndex:1];

    // Add this to whatever the current label text is
    typedWord.text = [NSString stringWithFormat:@"%@%@",typedWord.text,firstCharacter];

    // Trim off the first character
    NSString *remainingCharacters = [newText stringByReplacingCharactersInRange:NSMakeRange(0,1) withString:@""];

    //If we still have characters left, do the loop again.
    if (![remainingCharacters isEqualToString:@""])
        [self performSelector:@selector(updateLabel:) withObject:remainingCharacters afterDelay:0.2];
}

来源：https://stackoverflow.com/questions/8197406/uilabel-refresh