Question

我正在使用CoreText在多列中绘制文本（取决于iPad的方向）。

为了测试，我创建了一个由数字100 - 999组成的NSMutableString。这个文本跨越5列，其中1或2列在屏幕上（取决于方向）。

在我的主ViewController中，我添加了一个自定义的UIScrollView来保存这个文本，我希望它可以滚动。

我注意到滚动视图在我设置之前不会滚动：

[myScrollView setContentMode：UIViewContentModeRedraw];

我希望滚动iPad在旋转iPad时调用drawRect（以调整列数）！

我的问题是，它似乎在滚动时一遍又一遍地调用drawRect（因此分配越来越多的内存，也导致一些滞后）。

我将UIScrollView添加到我的主viewController中，如下所示：

myScrollView = [[CoreTextTestUIView alloc] init];
myScrollView.parentView = self;
if(FACING == @"PU" || FACING == @"PD")
{
    myScrollView.frame = CGRectMake(0,50,768,974);
}
else
{
    myScrollView.frame = CGRectMake(0,50,1024,718);
}
[myScrollView setContentMode:UIViewContentModeRedraw];
[container addSubview:myScrollView];

同样，我希望在旋转iPad时调用drawRect，因此列数可以更改......但是当我只是尝试滚动UIScrollView时，我不希望它调用drawRect。

有人能帮助我吗？

...

下面的

是我的UIScrollView的.m：

#import "CoreTextTestUIView.h"
#import <CoreText/CoreText.h>

@implementation CoreTextTestUIView

@synthesize parentView;


NSMutableString *testText;



-(id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if(self)
    {
        // Initialization code

        //set BG color
        self.backgroundColor = [[UIColor alloc] initWithRed:134 green:166 blue:228 alpha:1.0];

        //UIScrollView Stuff
        //self.delegate = self;
        self.scrollEnabled = YES;
        self.pagingEnabled = YES;
        self.userInteractionEnabled = YES;
        [self becomeFirstResponder];
        self.showsVerticalScrollIndicator = NO;
        self.showsHorizontalScrollIndicator = NO;
        self.bounces = NO;
        self.alwaysBounceHorizontal = YES;
        self.alwaysBounceVertical = NO;

        //generate long text
        testText = [[NSMutableString alloc] initWithString:@""];
        for(int i = 100; i < 1000; i++)
        {
            [testText appendString:[NSString stringWithFormat:@"%i ",i]];
        }

        self.alpha = 0.0;
        [self fadeIn];
    }
    return self;
}



-(void)fadeIn
{
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:1.0];  
    [UIView setAnimationDelegate:self]; 
    //[UIView setAnimationDidStopSelector:@selector(animationFinished:finished:context:)];  
    self.alpha = 1.0;
    [UIView commitAnimations];
}



// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
-(void)drawRect:(CGRect)rect
{

    NSMutableAttributedString *string = [[NSMutableAttributedString alloc] initWithString:[NSString stringWithFormat:@"%@",testText]];

    //set font
    CTFontRef helvetica = CTFontCreateWithName(CFSTR("Helvetica"), 40.0, NULL);
    [string addAttribute:(id)kCTFontAttributeName
                   value:(id)helvetica
                   range:NSMakeRange(0, [string length])];


    //layout master
    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)string);

    //flip the coordinate system
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);
    CGContextTranslateCTM(context, 0, self.bounds.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    int textPos = 0;
    int columnIndex = 0;

    //how many columns? (orientation dependent)
    float howManyColumns;
    if(parentView.FACING == @"PU" || parentView.FACING == @"PD")
    {
        howManyColumns = 1.0;
    }
    else
    {
        howManyColumns = 2.0;
    }

    //create columns in loop
    while(textPos < [string length])
    {
        NSLog(@"column started");

        //column form
        CGMutablePathRef columnPath = CGPathCreateMutable();
        CGPathAddRect(columnPath, NULL, 
                      CGRectMake((self.bounds.size.width/howManyColumns*columnIndex), 0, 
                                 (self.bounds.size.width/howManyColumns),
                                 self.bounds.size.height));

        //column frame
        CTFrameRef columnFrame = CTFramesetterCreateFrame(framesetter, 
                                                             CFRangeMake(textPos, 0),
                                                             columnPath,
                                                             NULL);

        //use the column path
        CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(textPos, 0), columnPath, NULL);
        CFRange frameRange = CTFrameGetVisibleStringRange(frame);

        //draw
        CTFrameDraw(columnFrame, context);

        //cleanup
        CFRelease(columnFrame);
        CGPathRelease(columnPath);

        textPos += frameRange.length;
        columnIndex++;
    }

    //set scrollView content size
    int totalPages = (columnIndex+1)/howManyColumns;
    self.contentSize = CGSizeMake(totalPages*self.bounds.size.width, self.frame.size.height);

    //release
    CFRelease(framesetter);
    [string release];
}



-(void)dealloc
{
    [super dealloc];

    [parentView release];
    [testText release];
}


@end

Answer 1

看着这个，我看不到你在哪里设置你的scrollView的contentSize。如果未设置scrollView的contentSize，则不会启用滚动，并且只能看到适合scrollView当前区域的内容。此外，如果您的文本在配置中是静态的，请考虑优化一些正在发生的重绘，并将其添加到scrollView的子视图中。

Answer 2

这就是drawRect的工作原理。每次视图移动或更改或与其重叠时都会调用它。如果您正确管理内存，这应该不是问题。

自定义uiscrollview不滚动（使用coretext）

2 个答案: