OC记录1--UIPickerView

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UIPickerView官方描述:

A view that uses a spinning-wheel or slot-machine metaphor to show one or more sets of values.
A picker view displays one or more wheels that the user manipulates to select items. Each wheel—known as a component—has a series of indexed rows representing the selectable items. Each row displays a string or view so that the user can identify the item on that row. Users select items by rotating the wheels to the desired values, which align with a selection indicator.

译文:

使用旋转轮或狭缝机隐喻显示一组或多组值的视图。
选取器视图显示用户操纵选择项目的一个或多个轮子。每个车轮（称为组件）都有一系列代表可选项目的索引行。每行显示一个字符串或视图，以便用户可以识别该行上的项目。用户通过将车轮旋转到与选择指示符对齐的期望值来选择项目。

下面开始UIPickerView学习:

查看UIPickerView类中的.h文件

UIPickerView父类是UIView; 

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NS_CLASS_AVAILABLE_IOS(2_0) __TVOS_PROHIBITED @interface UIPickerView : UIView <NSCoding>

属性

1,显示选中指示器,目前设置为NO或者为YES都没有什么影响;

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@property(nonatomic)BOOL showsSelectionIndicator;

2,当前UIPickerView的component数,为只读属性;

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@property(nonatomic,readonly) NSInteger numberOfComponents;

方法

1,获取某一个component的行数: 

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- (NSInteger)numberOfRowsInComponent:(NSInteger)component;

2,获取某个component行的size大小: 

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- (CGSize)rowSizeForComponent:(NSInteger)component;

3,返回一个view,来自协议方法:pickerView:viewForRow:forComponent:reusingView:

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// returns the view provided by the delegate via pickerView:viewForRow:forComponent:reusingView:
// or nil if the row/component is not visible or the delegate does not implement 
// pickerView:viewForRow:forComponent:reusingView:
- (nullable UIView *)viewForRow:(NSInteger)row forComponent:(NSInteger)component;

4,刷新所有component和单个component:

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- (void)reloadAllComponents;//刷新所有component
- (void)reloadComponent:(NSInteger)component;//刷新单个component

5,滑动到某个component的某行,animated表示是否要动画效果:

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- (void)selectRow:(NSInteger)row inComponent:(NSInteger)component animated:(BOOL)animated;

6,获取当前选中的行, -1 if nothing selected:

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- (NSInteger)selectedRowInComponent:(NSInteger)component;
 // returns selected row. -1 if nothing selected

实现的2个协议: UIPickerViewDataSource,UIPickerViewDelegate

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@property(nullable,nonatomic,weak) id<UIPickerViewDataSource> dataSource;                // default is nil. weak reference
@property(nullable,nonatomic,weak) id<UIPickerViewDelegate>   delegate;                  // default is nil. weak reference

1,UIPickerViewDataSource

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@required //表示下面协议方法必须实现
//返回component的个数
// returns the number of 'columns' to display.
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView;
//返回某个component中行数
// returns the # of rows in each component..
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component;
@end

2,UIPickerViewDelegate,由@optional进行修饰,表示该协议下的方法可以选择性的实现:

2.1,设置component的宽和高

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// returns width of column and height of row for each component. 
- (CGFloat)pickerView:(UIPickerView *)pickerView widthForComponent:(NSInteger)component __TVOS_PROHIBITED;
- (CGFloat)pickerView:(UIPickerView *)pickerView rowHeightForComponent:(NSInteger)component __TVOS_PROHIBITED;

2.2,返回每一行的展示数据,数据类型是:NSString或者是NSAttributedString

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- (nullable NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component __TVOS_PROHIBITED;
- (nullable NSAttributedString *)pickerView:(UIPickerView *)pickerView attributedTitleForRow:(NSInteger)row forComponent:(NSInteger)component NS_AVAILABLE_IOS(6_0) __TVOS_PROHIBITED; // attributed title is favored if both methods are implemented

2.3,每一个component行数中的view,可以进行自定义:但必须是UILabel

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- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(nullable UIView *)view __TVOS_PROHIBITED;

example:

-(UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view{
    //设置字体大小;
    UILabel *lbl = (UILabel *)view;
    if (lbl == nil) {
        lbl = [[UILabel alloc]init];
        //在这里设置字体相关属性
        lbl.font = [UIFont systemFontOfSize:13];
        lbl.textColor = [UIColor grayColor];
        lbl.textAlignment = NSTextAlignmentCenter;
        [lbl setBackgroundColor:[UIColor clearColor]];
        if (component == 0) {
            lbl.textColor = [UIColor redColor];
        }
    }
    //重新加载lbl的文字内容
    lbl.text = [self pickerView:pickerView titleForRow:row forComponent:component];
    return lbl;
}

2.4,当前选中的component和row

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- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component __TVOS_PROHIBITED;

代码示例

默认大小

1,当UIPickerView没有设置frame值时,默认宽是320,高是216;

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