objective-c - drawRect 看到空数组

Question

drawtestViewController.m 中的按钮链接到 ChalkBoard.m 中的 pushPoint 操作。它使用 CGpoint 对象填充 pointArray。这个数组到处都是对象，除了从 drawRect 看的时候。似乎从 drawRect 我以某种方式引用了原始数组的空副本，但我找不到任何错误......

我已将整个项目上传到 http://dl.dropbox.com/u/42099382/drawtest.zip

---

drawtestViewController.m 中的按钮 Action

- (IBAction)myDo {
   NSLog(@"-Button was pressed");    
  [self.board pushPoint:CGPointMake(100, 100 )];
  [self.board pushPoint:CGPointMake(10, 100 )];
  [self.graphicView setNeedsDisplay];
}

---

//  ChalkBoard.h
#import <UIKit/UIKit.h>

@interface ChalkBoard : UIView
-(void)pushPoint:(CGPoint)point;
@property (nonatomic,retain) NSMutableArray *pointArray;
@end

---

//ChalkBoard.m
#import "ChalkBoard.h"

@implementation ChalkBoard
@synthesize pointArray;

- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor blackColor];
    }
    return self;
}

-(NSMutableArray *)pointArray 
{
    if(pointArray == nil) pointArray = [[NSMutableArray alloc]initWithCapacity:10];
    return pointArray;
}

-(void)pushPoint:(CGPoint)point{
    // this is called from drawtestViewController.m by button press
    // in here the array is full and growing by each button press
    [self.pointArray addObject:[NSValue valueWithCGPoint:point]];
   NSLog(@"-pushPoint executed, size is %u, array: %@",[self.pointArray count], pointArray);
}

- (void)drawRect:(CGRect)rect{
// here array is always empty
NSLog(@"-DrawRect executed, size is %u, array: %@",[pointArray count], pointArray);
    if ([pointArray count] >1){   
       ... some irrelevant code
    }
}

@end

---

NSLog output

2012-04-09 11:34:39.145 drawtest[5260:f803] -DrawRect executed, size is 0, array: (null)
2012-04-09 11:34:41.261 drawtest[5260:f803] -Button was pressed
2012-04-09 11:34:41.262 drawtest[5260:f803] -pushPoint executed, size is 1, array: (
    "NSPoint: {100, 100}"
)
2012-04-09 11:34:41.264 drawtest[5260:f803] -pushPoint executed, size is 2, array: (
    "NSPoint: {100, 100}",
    "NSPoint: {10, 100}"
)
2012-04-09 11:34:41.266 drawtest[5260:f803] -DrawRect executed, size is 0, array: (null)
2012-04-09 11:34:42.825 drawtest[5260:f803] -Button was pressed
2012-04-09 11:34:42.826 drawtest[5260:f803] -pushPoint executed, size is 3, array: (
    "NSPoint: {100, 100}",
    "NSPoint: {10, 100}",
    "NSPoint: {100, 100}"
)
2012-04-09 11:34:42.827 drawtest[5260:f803] -pushPoint executed, size is 4, array: (
    "NSPoint: {100, 100}",
    "NSPoint: {10, 100}",
    "NSPoint: {100, 100}",
    "NSPoint: {10, 100}"
)
2012-04-09 11:34:42.829 drawtest[5260:f803] -DrawRect executed, size is 0, array: (null)

Answer 1

问题实际上不在您的Chalkboard 类中，而是在您的drawtestViewcontroller 中。您的 myDo 操作将点添加到 self.board，但将 setNeedsDisplay 消息发送到 self.graphicView，这是还有一个 Chalkboard 但不是你添加点的那个。

所以您看到的第二条日志消息实际上来自一个完全不同的对象。