浅谈block使用方法
对于block他用着确实方便,好多人都非常迷茫,这里写了一个Demo解说block的使用方法
好多人都觉得block是用于后一个界面向前一个界面传值用的,事实上更详细的说是经常使用来界面之间的传值,事实上仅仅要须要传值不管是view之间还是controller之间还是view与controller之间都能够用block,当传值比較少时用block比使用代理更方便.
block创建后都在栈区存放的,block的语义特性必须用copy,通过copy能够将block从栈区放到堆区,保证每次使用block时block都存在,因此我们使用时经常要定义属性,使用属性是为了保存该block变量
例如以下举个样例解说
首先在project中创建两个类BlockViewController和BlockView
在BlockView中仅仅是为了创建几个button,在BlockViewController中使用,能够降低BlockViewController的代码任务量,可是BlockView中仅仅有一个实例变量button是,而且在延展中定义的,外部无法訪问到,当我们为button加入点击触发事件就须要获得button的tag值,这时就要把所点击button的tag获取到,来为不同的button加入响应事件
在BlockView.h中定义一个block变量和一个方法,方法的參数是block类型的
#import <UIKit/UIKit.h> //第一步：声明block typedef void(^ButtonActionBlock)(NSInteger tag); @interface BlockView : UIView -(void)buttonActionBlock:(ButtonActionBlock)didClickButton; @end
在BlockView.m中
<pre name="code" class="objc">#import "BlockView.h"
@interface BlockView ()
//Block
//block创建后都在栈区存放的,block的语义特性必须用copy,通过copy能够将block从栈区放到堆区,保证每次使用block时block都存在
@property (nonatomic, copy) ButtonActionBlock buttonActionBlock;
@property (nonatomic, strong) UIButton *button;
@end
@implementation BlockView
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
CGFloat x = 5;
CGFloat y = 5;
CGFloat width = 65;
CGFloat height = 40;
//创建button
for (int i = 0; i < 4; i ++) {
self.button = [UIButton buttonWithType:(UIButtonTypeSystem)];
self.button.frame = CGRectMake(x + i * (width + 10), y, width, height);
self.button.tag = 100 + i;
self.button.backgroundColor = [UIColor cyanColor];
self.button.layer.cornerRadius = 5;
self.button.layer.masksToBounds = YES;
[self.button setTitle:[NSString stringWithFormat:@"%d",i] forState:UIControlStateNormal];
[self.button addTarget:self action:@selector(handleButton:) forControlEvents:UIControlEventTouchUpInside];
[self addSubview:_button];
}
}
return self;
}
//处理button的点击事件,将tag值传给block的參数回调block
-(void)handleButton:(UIButton *)button
{
NSLog(@"???????????????3");
NSInteger tag = button.tag;
//第二步，回掉block
self.buttonActionBlock(tag),NSLog(@"???????????????6");
NSLog(@"???????????????7");
}
//该方法中self.buttonActionBlock = didClickButton;运行后会调用属性buttonActionBlock的setter方法,将block变量didClickButton传给setter方法的參数
-(void)buttonActionBlock:(ButtonActionBlock)didClickButton
{
NSLog(@"???????????????1");
NSLog(@"-----------didClickButton = %p",didClickButton);
self.buttonActionBlock = didClickButton;
}
//重写属性buttonActionBlock的setter方法,在此重写setter方法目的是为了表明该方法是把传进来的block变量进行深拷贝,复制到了堆区,并赋给了实例变量buttonActionBlock,使我们在不论什么时候都能使用block变量(block的创建后在栈区,出了方法就被回收,无法再使用)
- (void)setButtonActionBlock:(ButtonActionBlock)buttonActionBlock
{
NSLog(@"???????????????2");
if (_buttonActionBlock != buttonActionBlock) {
NSLog(@"++++++++buttonActionBlock = %p",buttonActionBlock);
_buttonActionBlock = [buttonActionBlock copy];
}
}
@end
BlockViewController.m文件里导入BlockView.h文件
BlockViewController.m文件中代码实现
#import "BlockViewController.h"
#import "BlockView.h"
// 获取RGB颜色
#define RGBA(r,g,b,a) [UIColor colorWithRed:r/255.0f green:g/255.0f blue:b/255.0f alpha:a]
@interface BlockViewController ()<UIScrollViewDelegate>
@property (nonatomic, strong) UIImageView *YJFImageView;
@end
@implementation BlockViewController
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
}
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.backgroundColor = RGBA(252, 230, 201, 1.0);
BlockView *blockView = [[BlockView alloc] initWithFrame:CGRectMake(10, 0, 320 - 20, 50)];
blockView.backgroundColor = [UIColor lightGrayColor];
[self.view addSubview:blockView];
//BlockView的对象blockView调用其方法buttonActionBlock:
//第三步。调用block
[blockView buttonActionBlock:^(NSInteger tag) {
//block的实现
NSLog(@"???????????????4");
[self handleButton:tag];
NSLog(@"???????????????5");
}];
[self createView];
}
//处理自己定义toolBar的点击事件
-(void)handleButton:(NSInteger)tag
{
switch (tag) {
//...button
case 100:
{
self.YJFImageView.image = LOADIMAGE(@"2", @"jpg");
}
break;
//...button
case 101:
{
self.YJFImageView.image = LOADIMAGE(@"5", @"jpg");
}
break;
//...button
case 102:
{
self.YJFImageView.image = LOADIMAGE(@"6", @"jpg");
}
break;
//...button
case 103:
{
self.YJFImageView.image = LOADIMAGE(@"4", @"jpg");
}
break;
default:
break;
}
}
-(void)createView
{
self.YJFImageView = [[UIImageView alloc] initWithFrame:CGRectMake(10, 52, 320 - 20, 568 - 64 - 75)];
self.YJFImageView.image = LOADIMAGE(@"8", @"jpg");
self.YJFImageView.userInteractionEnabled = YES;
[self.view addSubview:_YJFImageView];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
通过程序执行控制台输出结果例如以下:
点击button前:
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由此结合代码实现中打的log能够看出
<pre name="code" class="objc">didClickButton和传入属性的setter方法的參数是一个地址,则
,BlockView.m文件里
<pre name="code" class="objc">buttonActionBlock:方法中把didClickButton拷贝了一份到栈区,赋值给实例变量_buttonActionBlock
点击button后:
结合代码实现中打的log能够看出整个Block的运行过程,也能够通过打断的查看Block的运行过程
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时间： 2024-10-11 22:27:17