#import "UICollectionView+NoDataView.h"
#import <objc/runtime.h>
#import "NoDataView.h"
/**
消除警告
*/
@protocol CollectionViewDelegate <NSObject>
@optional
- (UIView *)noDataView;
- (UIImage *)noDataViewImage;
- (NSString *)noDataViewMessage;
- (UIColor *)noDataViewMessageColor;
- (NSNumber *)noDataViewCenterYOffset;
@end
@implementation UICollectionView (NoDataView)
/**
加载时, 交换方法
*/
+ (void)load {
// 只交换一次
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
Method reloadData = class_getInstanceMethod(self, @selector(reloadData));
Method replace_reloadData = class_getInstanceMethod(self, @selector(replace_reloadData));
method_exchangeImplementations(reloadData, replace_reloadData);
Method dealloc = class_getInstanceMethod(self, NSSelectorFromString(@"dealloc"));
Method replace_dealloc = class_getInstanceMethod(self, @selector(replace_dealloc));
method_exchangeImplementations(dealloc, replace_dealloc);
});
}
/**
在 ReloadData 的时候检查数据
*/
- (void)replace_reloadData {
[self replace_reloadData];
// 忽略第一次加载
if (![self isInitFinish]) {
[self havingData:YES];
[self setIsInitFinish:YES];
return ;
}
// 刷新完成之后检测数据量
dispatch_async(dispatch_get_main_queue(), ^{
NSInteger numberOfSections = [self numberOfSections];
BOOL havingData = NO;
for (NSInteger i = 0; i < numberOfSections; i++) {
if ([self numberOfItemsInSection:i] > 0) {
havingData = YES;
break;
}
}
[self havingData:havingData];
});
}
/**
展示占位图
*/
- (void)havingData:(BOOL)havingData {
// 不需要显示占位图
if (havingData) {
[self freeNoDataViewIfNeeded];
self.backgroundView = nil;
return ;
}
// 不需要重复创建
if (self.backgroundView) {
return ;
}
// 自定义了占位图
if ([self.delegate respondsToSelector:@selector(noDataView)]) {
self.backgroundView = [self.delegate performSelector:@selector(noDataView)];
return ;
}
// 使用自带的
UIImage *img = nil;
NSString *msg = @"暂无数据";
UIColor *color = [UIColor lightGrayColor];
CGFloat offset = 0;
// 获取图片
if ([self.delegate respondsToSelector:@selector(noDataViewImage)]) {
img = [self.delegate performSelector:@selector(noDataViewImage)];
}
// 获取文字
if ([self.delegate respondsToSelector:@selector(noDataViewMessage)]) {
msg = [self.delegate performSelector:@selector(noDataViewMessage)];
}
// 获取颜色
if ([self.delegate respondsToSelector:@selector(noDataViewMessageColor)]) {
color = [self.delegate performSelector:@selector(noDataViewMessageColor)];
}
// 获取偏移量
if ([self.delegate respondsToSelector:@selector(noDataViewCenterYOffset)]) {
offset = [[self.delegate performSelector:@selector(noDataViewCenterYOffset)] floatValue];
}
// 创建占位图
self.backgroundView = [self defaultNoDataViewWithImage :img message:msg color:color offsetY:offset];
}
/**
默认的占位图
*/
- (UIView *)defaultNoDataViewWithImage:(UIImage *)image message:(NSString *)message color:(UIColor *)color offsetY:(CGFloat)offset {
// 计算位置, 垂直居中, 图片默认中心偏上.
CGFloat sW = self.bounds.size.width;
CGFloat cX = sW / 2;
CGFloat cY = self.bounds.size.height * (1 - 0.618) + offset;
CGFloat iW = image.size.width;
CGFloat iH = image.size.height;
// 图片
UIImageView *imgView = [[UIImageView alloc] init];
imgView.frame = CGRectMake(cX - iW / 2, cY - iH / 2, iW, iH);
imgView.image = image;
// 文字
UILabel *label = [[UILabel alloc] init];
label.font = [UIFont systemFontOfSize:17];
label.textColor = color;
label.text = message;
label.textAlignment = NSTextAlignmentCenter;
label.frame = CGRectMake(0, CGRectGetMaxY(imgView.frame) + 24, sW, label.font.lineHeight);
// 视图
NoDataView * view = [[NoDataView alloc] init];
[view addSubview:imgView];
[view addSubview:label];
// 实现跟随 collectionView 滚动
[view addObserver:self forKeyPath:kNoDataViewObserveKeyPath options:NSKeyValueObservingOptionNew context:nil];
return view;
}
/**
监听
*/
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
if ([keyPath isEqualToString:kNoDataViewObserveKeyPath]) {
/**
在 collectionView 滚动 ContentOffset 改变时, 会同步改变 backgroundView 的 frame.origin.y
可以实现, backgroundView 位置相对于 collectionView 不动, 但是我们希望
backgroundView 跟随 collectionView 的滚动而滚动, 只能强制设置 frame.origin.y 永远为 0
兼容 MJRefresh
*/
CGRect frame = [[change objectForKey:NSKeyValueChangeNewKey] CGRectValue];
if (frame.origin.y != 0) {
frame.origin.y = 0;
self.backgroundView.frame = frame;
}
}
}
#pragma mark - 属性
/// 加载完数据的标记属性名
static NSString * const kCollectionViewPropertyInitFinish = @"kCollectionViewPropertyInitFinish";
/**
设置已经加载完成数据了
*/
- (void)setIsInitFinish:(BOOL)finish {
objc_setAssociatedObject(self, &kCollectionViewPropertyInitFinish, @(finish), OBJC_ASSOCIATION_ASSIGN);
}
/**
是否已经加载完成数据
*/
- (BOOL)isInitFinish {
id obj = objc_getAssociatedObject(self, &kCollectionViewPropertyInitFinish);
return [obj boolValue];
}
/**
移除 KVO 监听
*/
- (void)freeNoDataViewIfNeeded {
if ([self.backgroundView isKindOfClass:[NoDataView class]]) {
[self.backgroundView removeObserver:self forKeyPath:kNoDataViewObserveKeyPath context:nil];
}
}
- (void)replace_dealloc {
[self freeNoDataViewIfNeeded];
[self replace_dealloc];
NSLog(@"CollectionView 视图正常销毁");
}
@end
