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1. NSString and std::string convert to each other

//from stackoverflow//nsstring to stringNSString *strA = @"NSString";std::string *strB = new std::string([strA UTF8String]);//orstd::string strB([strA UTF8String]);//string to nsstringNSString *str = [NSString stringWithCString:string.c_str()                                    encoding:[NSString defaultCStringEncoding]];NSString *str = [NSString stringWithCString:string.c_str()                                    encoding:NSUTF8StringEncoding]; // for chinesestd::string param; // <-- inputNSString* result = [NSString stringWithUTF8String:param.c_str()];NSString* alternative = [[NSString alloc] initWithUTF8String:param.c_str()];//chinese[NSString stringWithCString:m_AnswerSheet.GetName().c_str()                                                       encoding:NSUTF8StringEncoding]

2. how does NSString implement trimRight?this may help: link

//this removes white space from both ends of a stringNSString *newString = [oldString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];//just wanna remove white space at the end of the string? read the link above for more detail.

3. convert std::vector and NSArray to each other

std::vector<std::string> strVec;for (int i = 0; i < [NSMutableArrayObject count]; i++) {   NSString *NS_Ans = (NSString *)[NSMutableArrayObject objectAtIndex:i];   std::string Str_Ans = *new std::string([NS_Ans UTF8String]);   strVec.push_back(Str_Ans);}return strVec;//std::vector<std::string> ansArray = getOneVector();           NSMutableArray *nsArray = [NSMutableArray array];for (int j = 0; j < ansArray.size(); j++) {   NSString *item = [NSString stringWithCString:ansArray[j].c_str() encoding:[NSString defaultCStringEncoding]];            [nsArray addObject:item];}return ansArray;            

4. NSString append

string = [NSString initWithFormat:@"%@,%@", string1, string2 ];string = [string1 stringByAppendingString:string2];string = [string stringByAppendingFormat:@"%@,%@",string1, string2];

5. Get uuid in cocoa .reference from 各種OS中生成UUID的方法

std::string CHelpFunction::stringWithUuid() {    CFUUIDRef uuidObj = CFUUIDCreate(nil);    NSString *uuidString = (NSString *)CFBridgingRelease(CFUUIDCreateString(nil, uuidObj));    CFRelease(uuidObj);    return [uuidString UTF8String];}

6. set UIView background image

UIColor *color = [UIColor colorWithPatternImage:[UIImage imageNamed:@"bg.png"]];[myLabel setBackgroundColor:color];

7. set UIImage a click event, suitable for other uiview i think. reference

UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapDetected)];singleTap.numberOfTapsRequired = 1;[PReArrowImage setUserInteractionEnabled:YES];[preArrowImage addGestureRecognizer:singleTap];-(void)tapDetected{    NSLog(@"single Tap on imageview");  }

8. save int value in nsdictionary

[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:m_quesIndex] forKey:@"index"];//geti = [[dic objectForKey:@"index"] intValue];

9. NSNotification

//sendNSNotificationCenter *nc = [NSNotificationCenter defaultCenter];NSDictionary *d = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:m_index] forKey:@"index"];[nc postNotificationName:@"viewClicked" object:self userInfo:d];//regist observer[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(viewClickAt:) name:@"quesViewClicked" object:nil];//do function- (void)quesViewClickAt:(NSNotification *)noti {    int index = [[[noti userInfo] objectForKey:@"index"] intValue];}//dealloc- (void)dealloc {    [[NSNotificationCenter defaultCenter] removeObserver:self];}

10. force close keyboard

[view endEditing:YES]; 

11. remove all subviews

NSArray *viewsToRemove = [self.view subviews];for (UIView *v in viewsToRemove) {    [v removeFromSuperview];}

12. limit the input

- (BOOL)textView:(nonnull UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(nonnull NSString *)text {    // Prevent crashing undo bug     if(range.length + range.location > textView.text.length)    {        return NO;    }        NSUInteger newLength = [textView.text length] + [text length] - range.length;    return newLength <= 1024;}

13. insert null object into NSMutableArray or NSMutableDictionary etc.

if ((NSNull *)[mPages objectAtIndex:showPos] == [NSNull null]) {        [mPages removeObjectAtIndex:showPos];}[mPages insertObject:mPage atIndex:showPos];[mPages removeObjectAtIndex:hidePos];[mPages insertObject:[NSNull null] atIndex:hidePos];

14. UIScrollView scoll to top

UPDATE FOR iOS 7[self.scrollView setContentOffset:    CGPointMake(0, -self.scrollView.contentInset.top) animated:YES];ORIGINAL[self.scrollView setContentOffset:CGPointZero animated:YES];or if you want to preserve the horizontal scroll position and just reset the vertical position:[self.scrollView setContentOffset:CGPointMake(self.scrollView.contentOffset.x, 0)    animated:YES];

15. UITextField 增加輸入框靠左邊距 link

UITextField *content = ......;//設置輸入左邊距CGRect frame = content.frame;frame.size.width = 5;UIView *leftView = [[UIView alloc] initWithFrame:frame];content.leftViewMode = UITextFieldViewModeAlways;content.leftView = leftView;

16. 多個UITextField，鍵盤return 改為 next->next->done

//set keyboardif (i == count - 1)    [contentText setReturnKeyType:UIReturnKeyDone];else   [contentText setReturnKeyType:UIReturnKeyNext];#pragma mark - TextFieldDelegate- (BOOL)textFieldShouldReturn:(nonnull UITextField *)textField {    NSInteger nextTag = textField.tag + 1;    // Try to find next responder    UIResponder* nextResponder = [textField.superview viewWithTag:nextTag];    if (nextResponder) {        // Found next responder, so set it.        [nextResponder becomeFirstResponder];    } else {        // Not found, so remove keyboard.        [textField resignFirstResponder];    }    return NO; // We do not want UITextField to insert line-breaks.}

17. ios系統號detect

#define SYSTEM_VERSION_EQUAL_TO(v)                  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedSame)#define SYSTEM_VERSION_GREATER_THAN(v)              ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedDescending)#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)#define SYSTEM_VERSION_LESS_THAN(v)                 ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedAscending)#define SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(v)     ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedDescending)if (SYSTEM_VERSION_LESS_THAN(@"8.0")) {   ...}

18. drawInRect: withAttributes:

UIFont *textFont = [UIFont fontWithName: @"Helvetica" size: 60];UIColor *textColor = [UIColor blackColor];NSMutableParagraphStyle *textStyle = [[NSMutableParagraphStyle defaultParagraphStyle] mutableCopy];textStyle.lineBreakMode = NSLineBreakByWordWrapping;textStyle.alignment = NSTextAlignmentCenter;    [textContent drawInRect:textRect withAttributes:@{NSFontAttributeName:textFont, NSForegroundColorAttributeName:textColor, NSParagraphStyleAttributeName:textStyle}];

19. 設置粗體文字

首先可以上這個網站：http://iosfonts.com/查看自己要用的字體是否支持粗體，然后使用下面方法

-(void)boldFontForLabel:(UILabel *)label{    UIFont *currentFont = label.font;    UIFont *newFont = [UIFont fontWithName:[NSString stringWithFormat:@"%@-Bold",currentFont.fontName] size:currentFont.pointSize];    label.font = newFont;}

20. 文件保存數據庫的問題

ios 往數據庫里寫保存文件路徑的時候，不要寫全路徑，因為軟件更新或者重新安裝沙盒路徑會變

更新的流程是這樣的：更新時，先在新的路徑里安裝新程序，然后把舊程序文件夾里的配置文件之類的文件拷貝到新的路徑里去，然后刪除舊程序

所以，如果數據庫里保存的是絕對路徑，那么軟件會找不到文件。所以要保存相對路徑。比如/var/mobile/applications/ECDD1B2D-E53D-4914-BDDB-F0578BADAA38/Documents/A/B/C/9A4613EA-232A-480C-9492-B34A00BE3CB6.txt
只寫/A/B/C/9A4613EA-232A-480C-9492-B34A00BE3CB6.txt就好，前半部分用系統方法獲取。

21. get UIView touch point

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {    UITouch *touch = [touches anyObject];    CGPoint point = [touch locationInView:self];    NSLog(@"x:%f,   y:%f", point.x, point.y);    if (!CGRectContainsPoint(centerView.frame, point)) {        [self removeFromSuperview];    }    }

22. UIView一些尺寸屬性

• frame：origin是相對于屏幕的點的坐標，size就是其尺寸
  
• bound: origin永遠是(0,0)，size也是尺寸
  
• center: 是View的中心點，但坐標是相對于屏幕的。如果需要相對自己的中心點，則需要用bound.origin來計算

UICollectionViewCell 不能用-(id)init{}，要用-(id)initWithFrame:(CGRect)frame;或者initWithCoder

autolayout
[tmpView addSubview:m_textLeftTime];
[m_textLeftTime setTranslatesAutoresizingMaskIntoConstraints:NO];

[tmpView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[m_imgClock]-0-[m_textLeftTime]"                                                                options:0                                                                metrics:nil                                                                  views:NSDictionaryOfVariableBindings(m_imgClock, m_textLeftTime)]];[tmpView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[tmpView]-(<=1)-[m_imgClock(==32)]"                                                                options:NSLayoutFormatAlignAllCenterY                                                                metrics:nil                                                                  views:NSDictionaryOfVariableBindings(tmpView, m_imgClock)]];[tmpView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[tmpView]-(<=1)-[m_textLeftTime]"                                                                options:NSLayoutFormatAlignAllCenterY                                                                metrics:nil                                                                  views:NSDictionaryOfVariableBindings(tmpView, m_textLeftTime)]];

memcmp(&(GetClientID()), &(mClientID), sizeof(mClientID)) compare unsigned char or other