iOS UISearchBar轻松改变搜索图标和占位符坐标

 //搜索框
    UISearchBar *searchBar = [[UISearchBar alloc] init];
//    searchBar.delegate = self;
    searchBar.frame = CGRectMake(10, 0, screenW-80, titleView.bounds.size.height);
    searchBar.layer.cornerRadius = 17;
    searchBar.layer.masksToBounds = YES;
    [searchBar.layer setBorderWidth:8];
    [searchBar.layer setBorderColor:[UIColor whiteColor].CGColor];  //设置边框为白色
    searchBar.placeholder = @"请输入目的地";
    searchBar.translucent = YES;
    searchBar.searchBarStyle = UISearchBarStyleProminent;
    //改变占位符的字体大小颜色
    UITextField * searchField = [searchBar valueForKey:@"_searchField"];
    [searchField setValue:[UIColor lightGrayColor] forKeyPath:@"_placeholderLabel.textColor"];
    [searchField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];
    //改变左边搜索图标坐标位置。后面的占位符苹果已经做好约束总是跟随在搜索图标后面。
    [searchBar setPositionAdjustment:UIOffsetMake(60, 0) forSearchBarIcon:UISearchBarIconSearch];
设置搜索栏中图片的位置偏移，图片的枚举如下：
typedef NS_ENUM(NSInteger, UISearchBarIcon) {

    UISearchBarIconSearch, //搜索图标

    UISearchBarIconClear, // 清除图标

    UISearchBarIconBookmark, // 书本图标

    UISearchBarIconResultsList, // 结果列表图标

};

下面是搜索框控件的一些代理方法：

- (BOOL)searchBarShouldBeginEditing:(UISearchBar *)searchBar;           

将要开始编辑时的回调，返回为NO，则不能编辑

- (void)searchBarTextDidBeginEditing:(UISearchBar *)searchBar;                  

已经开始编辑时的回调

- (BOOL)searchBarShouldEndEditing:(UISearchBar *)searchBar;                

将要结束编辑时的回调

- (void)searchBarTextDidEndEditing:(UISearchBar *)searchBar;                   

已经结束编辑的回调

- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText;   编辑文字改变的回调

- (BOOL)searchBar:(UISearchBar *)searchBar shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text ; 

编辑文字改变前的回调，返回NO则不能加入新的编辑文字

- (void)searchBarSearchButtonClicked:(UISearchBar *)searchBar;       

搜索按钮点击的回调

- (void)searchBarBookmarkButtonClicked:(UISearchBar *)searchBar;             

书本按钮点击的回调

- (void)searchBarCancelButtonClicked:(UISearchBar *)searchBar;               

取消按钮点击的回调

- (void)searchBarResultsListButtonClicked:(UISearchBar *)searchBar; 

搜索结果按钮点击的回调

- (void)searchBar:(UISearchBar *)searchBar selectedScopeButtonIndexDidChange:(NSInteger)selectedScope;

搜索栏的附加试图中切换按钮触发的回调

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