iOS开发之-Managing Keyboard

Keyboards and Input Methods

Configuring the Keyboard for Text Objects

You configure the attributes of the keyboard directly through the text objects of your application. The UITextField and UITextView classes both conform to the UITextInputTraits protocol, which defines the properties for configuring the keyboard. Setting these properties programmatically or in the Interface Builder inspector window causes the system to display the keyboard of the designated type.

Managing the Keyboard

Receiving Keyboard Notifications

When the keyboard is shown or hidden, iOS sends out the following notifications to any registered observers:

• UIKeyboardWillShowNotification
• UIKeyboardDidShowNotification
• UIKeyboardWillHideNotification
• UIKeyboardDidHideNotification

Each keyboard notification includes information about the size and position of the keyboard on the screen. You can access this information from the userInfo dictionary of each notification using the UIKeyboardFrameBeginUserInfoKey and UIKeyboardFrameEndUserInfoKey keys; the former gives the beginning keyboard frame, the latter the ending keyboard frame (both in screen coordinates). The size of the keyboard is not guaranteed to be the same.

Note: The rectangle contained in the UIKeyboardFrameBeginUserInfoKey and UIKeyboardFrameEndUserInfoKey properties of the userInfo dictionary should be used only for the size information it contains. Do not use the origin of the rectangle (which is always {0.0, 0.0}) in rectangle-intersection operations. Because the keyboard is animated into position, the actual bounding rectangle of the keyboard changes over time.

Displaying the Keyboard

You can programmatically display the keyboard for an editable text view by calling that view’s becomeFirstResponder method. Calling this method makes the target view the first responder and begins the editing process just as if the user had tapped on the view.

Dismissing the Keyboard

To dismiss the keyboard, you call the resignFirstResponder method of the text-based view that is currently the first responder. When a text view resigns its first responder status, it ends its current editing session, notifies its delegate of that fact, and dismisses the keyboard. 

Moving Content That Is Located Under the Keyboard

When the keyboard is displayed, all you have to do is reset the content area of the scroll view and scroll the desired text object into position. Thus, in response to a UIKeyboardDidShowNotification, your handler method would do the following:

1. Get the size of the keyboard.
2. Adjust the bottom content inset of your scroll view by the keyboard height.
3. Scroll the target text field into view.

Listing 4-1  Handling the keyboard notifications
// Call this method somewhere in your view controller setup code.
- (void)registerForKeyboardNotifications
{
    [[NSNotificationCenter defaultCenter] addObserver:self
            selector:@selector(keyboardWasShown:)
            name:UIKeyboardDidShowNotification object:nil];
 
   [[NSNotificationCenter defaultCenter] addObserver:self
             selector:@selector(keyboardWillBeHidden:)
             name:UIKeyboardWillHideNotification object:nil];
 
}
 
// Called when the UIKeyboardDidShowNotification is sent.
- (void)keyboardWasShown:(NSNotification*)aNotification
{
    NSDictionary* info = [aNotification userInfo];
    CGSize kbSize = [[info objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size;
 
    UIEdgeInsets contentInsets = UIEdgeInsetsMake(0.0, 0.0, kbSize.height, 0.0);
    scrollView.contentInset = contentInsets;
    scrollView.scrollIndicatorInsets = contentInsets;
 
    // If active text field is hidden by keyboard, scroll it so it's visible
    // Your application might not need or want this behavior.
    CGRect aRect = self.view.frame;
    aRect.size.height -= kbSize.height;
    if (!CGRectContainsPoint(aRect, activeField.frame.origin) ) {
        CGPoint scrollPoint = CGPointMake(0.0, activeField.frame.origin.y-kbSize.height);
        [scrollView setContentOffset:scrollPoint animated:YES];
    }
}
 
// Called when the UIKeyboardWillHideNotification is sent
- (void)keyboardWillBeHidden:(NSNotification*)aNotification
{
    UIEdgeInsets contentInsets = UIEdgeInsetsZero;
    scrollView.contentInset = contentInsets;
    scrollView.scrollIndicatorInsets = contentInsets;
}
           

Listing 4-2  Additional methods for tracking the active text field.
- (void)textFieldDidBeginEditing:(UITextField *)textField
{
    activeField = textField;
}
 
- (void)textFieldDidEndEditing:(UITextField *)textField
{
    activeField = nil;
}
           

Listing 4-3  Adjusting the frame of the content view and scrolling a field above the keyboard
- (void)keyboardWasShown:(NSNotification*)aNotification {
    NSDictionary* info = [aNotification userInfo];
    CGSize kbSize = [[info objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size;
    CGRect bkgndRect = activeField.superview.frame;
    bkgndRect.size.height += kbSize.height;
    [activeField.superview setFrame:bkgndRect];
    [scrollView setContentOffset:CGPointMake(0.0, activeField.frame.origin.y-kbSize.height) animated:YES];
}