iOS 开发问与答(28-38)

大家好，我是讯享网，很高兴认识大家。

28.LocalSubstitionCache 不生效

AMapLocation 和 LocalSubstitutionCache 有冲突，无法和后者同时使用。将 AMapLocation 换成苹果的 CoreLocation 即可。

29.如何将按钮图标置于按钮文本的右侧？

正常情况下，按钮图片（ImageView）位于按钮文本（titleLabel）的左侧。要将二者左右交换，有以下几种方法。其中，最简单的是第一个方法：

func flipButtonTitleImage(button:UIButton){// 将按钮图标置于文本右侧 button.transform = CGAffineTransformMakeScale(-1.0, 1.0); button.titleLabel!.transform = CGAffineTransformMakeScale(-1.0, 1.0); button.imageView?.transform = CGAffineTransformMakeScale(-1.0, 1.0); }

讯享网

或者修改二者的 Insets：

讯享网thebutton.titleEdgeInsets = UIEdgeInsetsMake(0, -thebutton.imageView.frame.size.width, 0, thebutton.imageView.frame.size.width); thebutton.imageEdgeInsets = UIEdgeInsetsMake(0, thebutton.titleLabel.frame.size.width, 0, -thebutton.titleLabel.frame.size.width);

或者子类化 UIButton 并覆盖这两个方法：

@implementation UIButtonSubclass - (CGRect)imageRectForContentRect:(CGRect)contentRect { CGRect frame = [super imageRectForContentRect:contentRect]; frame.origin.x = CGRectGetMaxX(contentRect) - CGRectGetWidth(frame) - self.imageEdgeInsets.right + self.imageEdgeInsets.left; return frame; } - (CGRect)titleRectForContentRect:(CGRect)contentRect { CGRect frame = [super titleRectForContentRect:contentRect]; frame.origin.x = CGRectGetMinX(frame) - CGRectGetWidth([self imageRectForContentRect:contentRect]); return frame; } @end

当然，最简单的还是第一个方法。

30.如何定制 JSQMessagesLoadEarlierHeaderView？

默认 JSQMessagesLoadEarlierHeaderView 显示一个按钮，标题为“Load Earlier Messages”。我们可以修改这个按钮，让它显示“加载更多历史消息”，如下图所示。

讯享网
在 JSQMessagesViewController 子类中实现这个方法：

讯享网// 数据源方法：设置除了 cell 之外的 View，比如 HeaderView - (UICollectionReusableView *)collectionView:(JSQMessagesCollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath { if (self.showLoadEarlierMessagesHeader && [kind isEqualToString:UICollectionElementKindSectionHeader]) { 
  
    
  // 如果是 JSQMessagesLoadEarlierHeaderView JSQMessagesLoadEarlierHeaderView *header = [collectionView dequeueLoadEarlierMessagesViewHeaderForIndexPath:indexPath]; // Customize header [header.loadButton setTitle:@"加载更多历史消息" forState:UIControlStateNormal]; return header; } return [super collectionView:collectionView viewForSupplementaryElementOfKind:kind atIndexPath:indexPath]; }

31.如何定制 JSQMessagesToolbarContentView

在左边 voice 按钮前加入一个 add 按钮：

UIButton *btn=[UIButton buttonWithType:UIButtonTypeContactAdd]; JSQMessagesToolbarContentView *contentView= self.inputToolbar.contentView; [contentView.leftBarButtonContainerView addSubview:btn];//add the new button contentView.leftBarButtonItemWidth=66; //make containerView wider to hold more buttons //remove unused leftBarButtonItem constraint for (NSLayoutConstraint *constraint in contentView.leftBarButtonItem.superview.constraints) { if(constraint.secondItem ==contentView.leftBarButtonItem &&constraint.firstAttribute ==NSLayoutAttributeLeading){ constraint.active=NO; } } // update two button constraint [contentView.leftBarButtonItem mas_makeConstraints:^(MASConstraintMaker *make) { make.width.equalTo(@30); }]; [btn mas_makeConstraints:^(MASConstraintMaker *make) { make.top.equalTo(btn.superview.mas_top); make.bottom.equalTo(btn.superview.mas_bottom); make.left.equalTo(btn.mas_left); make.width.equalTo(@30); }];

在右边 send 按钮前加入一个 add 按钮：

讯享网-(void)customInputToolbar{ UIButton *btn=[UIButton buttonWithType:UIButtonTypeContactAdd]; JSQMessagesToolbarContentView *contentView= self.inputToolbar.contentView; [contentView.rightBarButtonContainerView addSubview:btn];//add the new button contentView.rightBarButtonItemWidth=76; //make containerView wider to hold more buttons //remove unused rightBarButtonItem constraint for (NSLayoutConstraint *constraint in contentView.rightBarButtonItem.superview.constraints) { if(constraint.secondItem ==contentView.rightBarButtonItem &&constraint.firstAttribute ==NSLayoutAttributeLeading){ constraint.active=NO; } } // update two button constraint [contentView.rightBarButtonItem mas_makeConstraints:^(MASConstraintMaker *make) { make.width.equalTo(@40); }]; [btn mas_makeConstraints:^(MASConstraintMaker *make) { make.top.equalTo(btn.superview.mas_top); make.bottom.equalTo(btn.superview.mas_bottom); make.right.equalTo(contentView.rightBarButtonItem.mas_left); make.width.equalTo(@30); }]; [btn addTarget:self action:@selector(addAction:) forControlEvents:UIControlEventTouchUpInside]; // 设置 voice 按钮和 send 按钮 [contentView.leftBarButtonItem setImage:[UIImage imageNamed:@"chat_bottom_voice_press"] forState:UIControlStateNormal]; [contentView.leftBarButtonItem setImage:[UIImage imageNamed:@"chat_bottom_voice_nor"] forState:UIControlStateHighlighted]; [contentView.rightBarButtonItem setTitle:@"发送" forState:UIControlStateNormal]; }

32.如何判断 TextView 中回车键按下？

如果是 UITextField，可以用 textFieldShouldReturn(_) 委托方法。但 UITextView 中却没有类似的委托方法，因此只能用 textView(_, shouldChangeTextInRange:, replacementText:) 方法替代：

func textView(textView: UITextView, shouldChangeTextInRange range: NSRange, replacementText text: String) -> Bool { if text == "\n" { if !textView.text.isEmpty { textView.resignFirstResponder() ... ... // 回车键按下，进行相应处理 } return false; } return true; }

O-C 代码：

讯享网- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text { if([text isEqualToString:@"\n"]) { if( [textView.text length]>0){ [textView resignFirstResponder]; ... ... // 回车键按下，进行相应处理 } return NO; } return YES; }

33. 如何检测 UITextView 的 contentSize 被改变？

[self.inputToolbar.contentView.textView addObserver:self forKeyPath:NSStringFromSelector(@selector(contentSize)) options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:NULL];

然后实现 observeValueForKeyPath 方法，检测 contentSize 变化：

讯享网- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if (object == self.inputToolbar.contentView.textView && [keyPath isEqualToString:NSStringFromSelector(@selector(contentSize))]) { CGSize oldContentSize = [[change objectForKey:NSKeyValueChangeOldKey] CGSizeValue]; CGSize newContentSize = [[change objectForKey:NSKeyValueChangeNewKey] CGSizeValue]; CGFloat dy = newContentSize.height - oldContentSize.height; [self jsq_adjustInputToolbarForComposerTextViewContentSizeChange:dy]; [self jsq_updateCollectionViewInsets]; if (self.automaticallyScrollsToMostRecentMessage) { [self scrollToBottomAnimated:NO]; } } }

但是，UIKit 中的 KVO 兼容并不是非常可靠，特别在 iOS 9 中。替代的方案是子类化 UITextView 并覆盖 setContentSize 方法。

34. 第三方库编译出现错误“Too many arguments to function call,expected 0,have 3”

例如，编译 nimbus 库时， NIButtonUtilities.m 中的 method(: : :)方法调用出现编译错误：Too many arguments to function call,expected 0,have 3

根据 2014 WWDC 视频中 Session 417 “What’s New in LLVM” 所述，编译器会强制要求对 objc_msgSend 使用强类型声明。例如：

typedef void (*send_type)(void*, SEL, void*); send_type func = (send_type)objc_msgSend; func(anItem.callback_object, NSSelectorFromString(anItem.selector), dict);

注意 sent_type 的使用。现在 objc_msgSend 变成了一个强类型。如果是调用实例方法，也是同样：

讯享网typedef void (*send_type)(void*, SEL, void*); send_type methodInstance = (send_type)[SomeClass instanceMethodForSelector:someSelector]; methodInstance(self, someSelector, someArgument);

35. 在 lldb 中如何打印 indexPath.row?

当我们使用 lldb 命令 p indexPath.row 时，总是报错：error: property ‘row’ not found on object of type ‘NSIndexPath *’

其实，只需要换成如下命令即可：

(lldb) p (NSInteger)[indexPath section] (NSInteger) $15 = 0

36. 如何用 CocoaHttpServer 实现一个 https 服务器？

继承 HTTPConnection 类：

讯享网@interface MyHTTPConnection : HTTPConnection

在 HTTPConnection 子类中，实现 - (BOOL)isSecureServer 方法并返回 YES，表示支持 https。

制作一个 SSL 自签名证书（见问题 37），安装到钥匙串，然后导出为 .p12 文件，记住导出密码。

制作证书时需要注意 /CN 参数必须指定主机名，比如 /CN 参数指定为 127.0.0.1，则访问时只能用 https://127.0.0.1，而不能用 https://localhost 替代。

实现 sslIdentityAndCertificates 方法：

- (NSArray *)sslIdentityAndCertificates { SecIdentityRef identityRef = NULL; SecCertificateRef certificateRef = NULL; SecTrustRef trustRef = NULL; NSString *thePath = [[NSBundle mainBundle] pathForResource:@"127.0.0.1" ofType:@"p12"]; NSData *PKCS12Data = [[NSData alloc] initWithContentsOfFile:thePath]; CFDataRef inPKCS12Data = (__bridge CFDataRef)PKCS12Data; CFStringRef password = CFSTR("你导出 .p12 的密码"); const void *keys[] = { kSecImportExportPassphrase }; const void *values[] = { password }; CFDictionaryRef optionsDictionary = CFDictionaryCreate(NULL, keys, values, 1, NULL, NULL); CFArrayRef items = CFArrayCreate(NULL, 0, 0, NULL); OSStatus securityError = errSecSuccess; securityError = SecPKCS12Import(inPKCS12Data, optionsDictionary, &items); if (securityError == 0) { CFDictionaryRef myIdentityAndTrust = CFArrayGetValueAtIndex (items, 0); const void *tempIdentity = NULL; tempIdentity = CFDictionaryGetValue (myIdentityAndTrust, kSecImportItemIdentity); identityRef = (SecIdentityRef)tempIdentity; const void *tempTrust = NULL; tempTrust = CFDictionaryGetValue (myIdentityAndTrust, kSecImportItemTrust); trustRef = (SecTrustRef)tempTrust; } else { NSLog(@"Failed with error code %d",(int)securityError); return nil; } SecIdentityCopyCertificate(identityRef, &certificateRef); NSArray *result = [[NSArray alloc] initWithObjects:(__bridge id)identityRef, (__bridge id)certificateRef, nil]; return result; }

讯享网[settings setObject:(NSString *)kCFStreamSocketSecurityLevelNegotiatedSSL forKey:(NSString *)kCFStreamSSLLevel]

替换为：

[settings setObject:[NSNumber numberWithInteger:2] forKey:GCDAsyncSocketSSLProtocolVersionMin]; [settings setObject:[NSNumber numberWithInteger:2] forKey:GCDAsyncSocketSSLProtocolVersionMax];

在启动 HTTPServer （调用 startServer ）之前，使用 setConnectionClass 方法将 HTTPConnecdtion 替换为 MyHTTPConnection：

讯享网[httpServer setConnectionClass:[MyHTTPConnection class]];

37 如何制作 SSL 自签名证书？

1. CA 私钥 openssl genrsa -out myCA.key 2048 2. CA 证书 openssl req -x509 -new -key myCA.key -out myCA.cer -days 35600 -subj /CN="Yunnan Yuan Xin" 3. SSL 证书私钥 openssl genrsa -out myserver.key 2048 4. CSR openssl req -new -out sslcert.req -key myserver.key -subj /CN=127.0.0.1 5. ssl 证书 openssl x509 -req -in sslcert.req -out sslcert.cer -CAkey myCA.key -CA myCA.cer -days 36500 -CAcreateserial -CAserial serial 6. 合并私钥及证书 openssl pkcs12 -export -out sslcert.pfx -inkey myserver.key -in sslcert.cer

38. 实现本地 HTTPs 服务器后，在 iOS 9 上无法访问

讯享网 [settings setObject:(NSString *)kCFStreamSocketSecurityLevelNegotiatedSSL forKey:(NSString *)kCFStreamSSLLevel];