Adding error handling to the connection flow.

remoting/ios/app/pin_entry_view.mm

Index: remoting/ios/app/pin_entry_view.mm
diff --git a/remoting/ios/app/pin_entry_view.mm b/remoting/ios/app/pin_entry_view.mm
index 87a5a6b2523419773823b9488783e7d36bfe962b..1a8fbd5aa17b3f22b3c1ca69575c01a80279a37a 100644
--- a/remoting/ios/app/pin_entry_view.mm
+++ b/remoting/ios/app/pin_entry_view.mm
@@ -12,10 +12,10 @@
 #import "remoting/ios/app/remoting_theme.h"
 
 static const CGFloat kMargin = 5.f;
-static const CGFloat kPadding = 6.f;
+static const CGFloat kPadding = 8.f;
 static const CGFloat kLineSpace = 12.f;
 
-@interface PinEntryView () {
+@interface PinEntryView ()<UITextFieldDelegate> {
   UISwitch* _pairingSwitch;
   UILabel* _pairingLabel;
   MDCFloatingButton* _pinButton;
@@ -52,6 +52,7 @@ static const CGFloat kLineSpace = 12.f;
                    action:@selector(didTapPinEntry:)
          forControlEvents:UIControlEventTouchUpInside];
     _pinButton.translatesAutoresizingMaskIntoConstraints = NO;
+    _pinButton.enabled = NO;
     [self addSubview:_pinButton];
 
     _pinEntry = [[UITextField alloc] init];
@@ -65,6 +66,7 @@ static const CGFloat kLineSpace = 12.f;
               NSForegroundColorAttributeName :
                   [UIColor colorWithRed:1.f green:1.f blue:1.f alpha:0.5]
             }];
+    _pinEntry.delegate = self;
     [self addSubview:_pinEntry];
   }
   return self;
@@ -111,6 +113,34 @@ static const CGFloat kLineSpace = 12.f;
   [_pairingLabel sizeToFit];
 }
 
+#pragma mark - UITextFieldDelegate
+
+- (BOOL)textField:(UITextField*)textField
+    shouldChangeCharactersInRange:(NSRange)range
+                replacementString:(NSString*)string {
+  if (textField == _pinEntry) {
+    NSUInteger length = _pinEntry.text.length - range.length + string.length;
+    _pinButton.enabled = length >= 6;
+  }
+  return YES;
+}
+
+- (BOOL)textFieldShouldReturn:(UITextField*)textField {
+  NSLog(@"textFieldShouldReturn");
+  if ([_pinButton isEnabled]) {
+    [self didTapPinEntry:textField];
+    return YES;
+  }
+  return NO;
+}
+
+#pragma mark - Public
+
+- (void)clearPinEntry {
+  _pinEntry.text = @"";
+  _pinButton.enabled = NO;
+}
+
 #pragma mark - Private
 
 - (void)didTapPinEntry:(id)sender {