objective-c - drawRect 查看空数组
<p><p>drawtestViewController.m 中的按钮链接到 ChalkBoard.m 中的 pushPointAction 。它用 CGpoint 对象填充 pointArray。这个数组到处都是对象，除非从 drawRect 中查看。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...</p>
<p>我已将整个项目上传至 <a href="http://dl.dropbox.com/u/42099382/drawtest.zip" rel="noreferrer noopener nofollow">http://dl.dropbox.com/u/42099382/drawtest.zip</a> </p>
<hr/>
<p>drawtestViewController.m 中的按钮操作</p>
<pre><code>- (IBAction)myDo {
NSLog(@"-Button was pressed");
;
;
;
}
</code></pre>
<hr/>
<pre><code>//ChalkBoard.h
#import <UIKit/UIKit.h>
@interface ChalkBoard : UIView
-(void)pushPoint:(CGPoint)point;
@property (nonatomic,retain) NSMutableArray *pointArray;
@end
</code></pre>
<hr/>
<pre><code>//ChalkBoard.m
#import "ChalkBoard.h"
@implementation ChalkBoard
@synthesize pointArray;
- (id)initWithFrame:(CGRect)frame
{
self = ;
if (self) {
self.backgroundColor = ;
}
return self;
}
-(NSMutableArray *)pointArray
{
if(pointArray == nil) pointArray = [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
];
NSLog(@"-pushPoint executed, size is %u, array: %@",, pointArray);
}
- (void)drawRect:(CGRect)rect{
// here array is always empty
NSLog(@"-DrawRect executed, size is %u, array: %@",, pointArray);
if ( >1){
... some irrelevant code
}
}
@end
</code></pre>
<hr/>
<pre><code>NSLog output
2012-04-09 11:34:39.145 drawtest -DrawRect executed, size is 0, array: (null)
2012-04-09 11:34:41.261 drawtest -Button was pressed
2012-04-09 11:34:41.262 drawtest -pushPoint executed, size is 1, array: (
"NSPoint: {100, 100}"
)
2012-04-09 11:34:41.264 drawtest -pushPoint executed, size is 2, array: (
"NSPoint: {100, 100}",
"NSPoint: {10, 100}"
)
2012-04-09 11:34:41.266 drawtest -DrawRect executed, size is 0, array: (null)
2012-04-09 11:34:42.825 drawtest -Button was pressed
2012-04-09 11:34:42.826 drawtest -pushPoint executed, size is 3, array: (
"NSPoint: {100, 100}",
"NSPoint: {10, 100}",
"NSPoint: {100, 100}"
)
2012-04-09 11:34:42.827 drawtest -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 -DrawRect executed, size is 0, array: (null)
</code></pre></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>问题实际上不在您的 <code>Chalkboard</code> 类中，而是在您的 <code>drawtestViewcontroller</code> 中。您的 <code>myDo</code> 操作将点添加到 <code>self.board</code>，但将 <code>setNeedsDisplay</code> 消息发送到 <code>self.graphicView</code>，即也是一个 <code>Chalkboard</code>，但不是您添加点的那个。</p>
<p>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。</p></p>
<p style="font-size: 20px;">关于objective-c - drawRect 查看空数组，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/10070872/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/10070872/
</a>
</p>
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