我使用UIPickerView寫了一個城市選擇器,可是我發現在省份滾輪滾動的時候如果同時再滾動城市滾輪會崩潰,代碼如下:
@interface GLViewController ()<UIPickerViewDataSource, UIPickerViewDelegate>
@property (nonatomic, strong) NSArray *provinces;
@property (nonatomic, weak) UIPickerView *pickerView;
@end
@implementation GLViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// 1.建立pickerview
// pickerview有預設的frame
UIPickerView *pickerView = [[UIPickerView alloc] init];
pickerView.dataSource = self;
pickerView.delegate = self;
[self.view addSubview:pickerView];
self.pickerView = pickerView;
}
#pragma mark - UIPickerViewDataSource
// 告訴系統有多少列
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
return 2;
}
// 告訴系統有多少行
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
if (0 == component) {
// 省份列
return self.provinces.count;
}else
{
// 城市列
// 擷取第0列選中的行
NSInteger selectIndex = [self.pickerView selectedRowInComponent:0];
// 1.根據第0列選中的行數擷取對應的省
NJProvince *province = self.provinces[selectIndex];
// 2.擷取對應省份對應的城市
NSArray *cities = province.cities;
// 3.傳回城市的個數r
return cities.count;
}
}
#pragma mark - UIPickerViewDelegate
// 告訴系統每一行顯示什麼内容
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
NSLog(@"titleForRow");
if (0 == component) {
// 省份
// 1.擷取對應行對應的省份模型
NJProvince *province = self.provinces[row];
// 2.傳回省份的名稱
return province.name;
}else
{
// 城市列
// 0.擷取第0列選中的行數
NSInteger selectIndex = [pickerView selectedRowInComponent:0];
// 1.擷取對應的省份
NJProvince *province = self.provinces[selectIndex];
// 2.擷取對應的城市
return province.cities[row];
}
}
// 監聽pickerView的選中
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
// 判斷是否修改了第0列(省份列)
if (0 == component) {
// 重新整理第1列對應的資料
[pickerView reloadComponent:1];
// 讓第1列滾動到第0行
[pickerView selectRow:0 inComponent:1 animated:YES];
}
}
#pragma mark - 懶加載
- (NSArray *)provinces
{
if (_provinces == nil) {
// 加載資源
NSArray *array = [NSArray arrayWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"cities" ofType:@"plist"]];
// 轉換為模型
NSMutableArray *models = [NSMutableArray arrayWithCapacity:array.count];
for (NSDictionary *dict in array) {
NJProvince *province = [NJProvince provinceWithDictionary:dict];
[models addObject:province];
}
_provinces = [models copy];
}
return _provinces;
}
@end
這個崩潰現象是由于省份滾輪在滾動過程中[pickerView selectedRowInComponent]一直在變化,而代理方法-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component隻有在滾輪停止滾動式才會調用。我們滾動城市的滾輪時會調用代理- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component,進而需要調用[pickerView selectedRowInComponent],此時如果省份也是滾動的擷取到得省份的行是變化的,是以在滾動城市取資料過程中出現的數組越界,解決方法就是設定一個省份行的屬性,隻有在停止滾動的時候在-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component設定,在其他代理中通過這個索引更新資料。于是我用了另一種寫法:
@interface TCityPickerView ()<UIPickerViewDataSource, UIPickerViewDelegate>
@property (nonatomic, weak) UIPickerView *pickerView;
@property (nonatomic, strong) NSArray *citiesArray;
@property (nonatomic, assign) NSInteger provinceIndex;
@end
@implementation TCityPickerView
#pragma mark - public
+ (instancetype)cityPickerView {
TCityPickerView *pickerView = [[TCityPickerView alloc] init];
pickerView.backgroundColor = kColorBarBg;
pickerView.show = NO;
pickerView.frame = CGRectMake(0, kScreenHeight - 64, kScreenWidth, 244);
[pickerView hiddenPickerView];
return pickerView;
}
#pragma mark - lazy
- (NSArray *)citysArray {
if (!_citiesArray) {
NSString *filePath = [[NSBundle mainBundle] pathForResource:@"cities.plist" ofType:nil];
_citiesArray = [NSArray arrayWithContentsOfFile:filePath];
}
return _citiesArray;
}
#pragma mark - init
- (instancetype)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
self.provinceIndex = 0;
[self initSubViews];
}
return self;
}
- (void)initSubViews {
UIPickerView *picker = [[UIPickerView alloc] init];
picker.dataSource = self;
picker.delegate = self;
[self addSubview:picker];
self.pickerView = picker;
}
#pragma mark - UIPickerViewDataSource
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {
return 2;
}
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component {
if (component == 0) {
return self.citysArray.count;
} else {
return [self.citysArray[self.provinceIndex][@"cities"] count];
}
}
#pragma mark - UIPickerViewDelegate
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component {
NSString *title = nil;
if (component == 0) {
title = self.citysArray[row][@"name"];
} else {
title = self.citysArray[self.provinceIndex][@"cities"][row];
}
return title;
}
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component {
if (component == 0) {
self.provinceIndex = [pickerView selectedRowInComponent:0];
[self.pickerView reloadComponent:1];
[self.pickerView selectRow:0 inComponent:1 animated:YES];
}
}
@end