当TableView没有数据源时，如何显示占位图片？

有时候项目中有这样的需求，页面包含一个UITableVeiw，当没有数据的时候显示一张占位图片，点击图片可以重新刷新数据。效果图如下：

有数据时.png
没数据时.png

思路

为UITableView增加个Category，利用方法method_exchangeImplementations交换reloadData方法为real_ReloadData，在real_ReloadData方法内判断是否有数据源，再动态显示占位的UIView。

在创建UITableView的地方一句代码设置占位控件。

    tableView.placeHolderView = [[PlaceholderView alloc]initWithFrame:tableView.bounds onTapView:^{
      //点击占位图片
    }];
    [self.view addSubview:tableView];

UITableView+Placeholder.h文件

#import <UIKit/UIKit.h>
@interface UITableView (Placeholder)
/* 占位图 */
@property (nonatomic, strong) UIView *placeHolderView;
@end

UITableView+Placeholder.m文件

#import "UITableView+Placeholder.h"
#import <objc/runtime.h>

@implementation UITableView (Placeholder)

+ (void)load
{
    //交换刷新方法
    Method reloadData =class_getInstanceMethod(self,  @selector(reloadData));
    Method real_ReloadData =class_getInstanceMethod(self, @selector(real_ReloadData));
    method_exchangeImplementations(reloadData, real_ReloadData);
}

-(void)real_ReloadData
{
    [self dataIsEmpty];
    [self real_ReloadData];
}

/** 判断是否有数据源，没有数据源则显示占位图片  */
- (void)dataIsEmpty
{
    BOOL isEmpty = YES;
    id<UITableViewDataSource> dataSourse = self.dataSource;
    //检测是否有数据源
    if ([dataSourse respondsToSelector:@selector(numberOfSectionsInTableView:)]) {//group
        NSInteger sections = [dataSourse numberOfSectionsInTableView:self];
        if (sections >0) {
            isEmpty = NO;
        }
    }else if([dataSourse respondsToSelector:@selector(tableView:numberOfRowsInSection:)]){//plain
        NSInteger rows = [dataSourse tableView:self numberOfRowsInSection:0];
        if (rows >0) {
            isEmpty = NO;
        }
    }
    if (isEmpty) {//显示占位图
        [self.placeHolderView removeFromSuperview];
        [self addSubview:self.placeHolderView];
    }else{//移除占位图片
        [self.placeHolderView removeFromSuperview];
    }
}
- (void)setPlaceHolderView:(UIView *)placeHolderView
{
    objc_setAssociatedObject(self, @selector(placeHolderView), placeHolderView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (UIView *)placeHolderView
{
    return objc_getAssociatedObject(self, @selector(placeHolderView));
}

自定义占位的UIView 为PlaceholderView

PlaceholderView.h文件

#import <UIKit/UIKit.h>
//点击后的回调
typedef void(^TapBlock)();
@interface PlaceholderView : UIView
@property(nonatomic,copy)TapBlock onTapBlock;
- (instancetype)initWithFrame:(CGRect)frame onTapView:(TapBlock)onTapBlock;
@end

PlaceholderView.m文件

#import "PlaceholderView.h"

@implementation PlaceholderView
{
    UIImageView *_imageView;
}

- (instancetype)initWithFrame:(CGRect)frame onTapView:(TapBlock)onTapBlock
{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor whiteColor];
        self.onTapBlock = onTapBlock;
        [self setupSubViews];
    }
    return self;
}
-(void)setupSubViews
{
    UIImageView *imageView =[[UIImageView alloc]init];
    imageView.userInteractionEnabled = YES;
    imageView.contentMode = UIViewContentModeCenter;
    [imageView setImage:[UIImage imageNamed:@"nodataPlaceholder"]];
    _imageView = imageView;
    [self addSubview:imageView];
    
    [self addGestureRecognizer:[[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(onTapView:)]];
}
-(void)layoutSubviews
{
    [super layoutSubviews];
    _imageView.frame = self.bounds;
}
/** 增加点击手势 **/
-(void)onTapView:(UITapGestureRecognizer *)recognizer
{
    if (self.onTapBlock) {
        self.onTapBlock();
    }
}

这样当这个需求发生变化时，改动相对来说更小。当然，还可以把设置placeholderView的代码也封装到UItableView分类的init里面去。
点击下载Demo 有什么错误欢迎批评指正 。