IOS: action with enter key of iPad KeyBoard

I have two textfield, in first textfield I write "Hello" and when I push 开发者_运维知识库enter in iPad keyboard, I want that in second textfield appear "World"; How can I use enter to create an action in my application?

You would typically assign your view controller as the text field's delegate and then implement the textFieldShouldReturn: method, e.g.:

- (BOOL)textFieldShouldReturn:(UITextField *)textField {
    otherTextField.text = @"World"
    return YES;
}

You can do that by implementing the UITextFieldDelegate protocol in your controller. For instance you could do something like:

- (BOOL)textFieldShouldReturn:(UITextField *)textField {
    if (textField == theFirstTextField && [textField.text isEqualToString:@"Hello"]) {
        theSecondTextField.text = @"World";
    }
    return YES;
}

Set your view controller to be the textfield's delegate then implement

-(BOOL)textFieldShouldReturn:(UITextField *)textField

this gets called when the enter button is pushed on the keyboard.

This is roughly what you'd do. Tweaking to condition around device-type (if you truly want iPad only):

#pragma mark - UITextField Delegate

- (BOOL)textFieldShouldReturn:(UITextField *)textField 
{
    if (textField == self.firstTextField && [textField.text isEqualToString:@"Hello"]) {
        self.secondTextField.text = @"World";
    }
    return YES;
}