[NSDecimalNumber Length]：发送到实例的无法识别的选择器

Question

我在简单的 TableViewController 项目上遇到错误，因为看起来我试图将 NSDecimalNumber 对象强制放入名为 CheckValue.text 的标签的文本中作为 cellForRowAtIndexPath方法。

说实话，我正在尝试这样做，因为我需要 NSDecimalNumber 的值显示在 TableCell 上。有人能帮忙吗，因为我觉得我快要中弹了？

这是来自 TableViewController.m

的代码

#import "TableViewController.h"
#import "TableCell.h"

@interface TableViewController ()
{
    NSMutableData *webData;
    NSURLConnection *connection;
    NSMutableArray *array;
}

@end

@implementation TableViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    // Uncomment the following line to preserve selection between presentations.
    // self.clearsSelectionOnViewWillAppear = NO;
    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;
    // Get an array from web and Populate Check Arrays with New Data as above ...

    [self GetDatabaseData];
}

-(void)GetDatabaseData{
    NSURL *blogURL = [NSURL URLWithString:JSON_URL];
    NSData *jsonData = [NSData dataWithContentsOfURL:blogURL];
    NSError *error = nil;

    //NSDictionary *dataDictionary = [NSJSONSerialization JSONObjectWithData: jsonData options:0 error:&error];
    NSArray *TransactionArray = [NSJSONSerialization JSONObjectWithData: jsonData options:0 error:&error];

    NSDecimalNumber *check_total = [NSDecimalNumber zero];

    NSString *current_check;

    // Loop through Json objects, create question objects and add them to our questions array
    for (int i = 0; i < TransactionArray.count; i++)
    {
        NSDictionary *jsonElement = TransactionArray[i];

        // Accumulate if this is part of the same check.
       NSDecimalNumber *line_total = [NSDecimalNumber decimalNumberWithString:jsonElement[@"tran_value"]];

        // Decide if this is Element Belong to the Last Check number.
        if (jsonElement[@"tran_check"] == current_check){
            check_total = line_total; // Reset Check Total to be the Value of this Line on NEW Checks
        }
        else{
           check_total = [check_total decimalNumberByAdding:line_total];     //Add this Line Value to the Running Check Total
        }

        current_check = jsonElement[@"tran_check"]; // Make this Check number the Current Check for Totalizing.

        _Checknumbers = @[jsonElement[@"tran_check"]];
        _CheckTime = @[jsonElement[@"tran_hour"]];
        _CheckValue = @[check_total];
    }
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return _Checknumbers.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    //  UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"Cell" forIndexPath:indexPath];

    static NSString *CellIdentifier = @"TableCell";

    TableCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    int row = [indexPath row];

    cell.CheckLabel.text = _Checknumbers[row];
    cell.CheckValue.text = _CheckValue[row];
    cell.CheckTime.text = _CheckTime[row];

    return cell;
}

@end

Answer 1

NSDecimalNumber 继承自 NSNumber 因此 NSNumberFormatter 格式化程序可用于获取您需要的字符串表示形式。

这是一个示例，可以根据您的需要进行更改：

- (NSString *)formatNumber:(NSDecimalNumber *)number {
    NSNumberFormatter *numberFormatter = [NSNumberFormatter new];
    [numberFormatter setMinimumFractionDigits:2];
    numberFormatter.usesGroupingSeparator = YES;

    return [numberFormatter stringFromNumber:number];
}

示例：

number     returns
12456.3  12,456.30  
12           12.00  
12.3456      12.35

我在示例计算器应用程序中使用了它。

如果formatNumber方法添加到TableViewController class:

cell.CheckValue.text = [self formatNumber:_CheckValue[row]];

为了更容易调试（总是一件好事）

NSDecimalNumber *checkValueDecimal = _CheckValue[row];
NSString *checkValueString = [self formatNumber:_ checkValueDecimal];
cell.label.text = numberString;

这样可以检查每个步骤，编译器会在发布版本上优化它。

Answer 2

您可以使用 NSDecimalNumber 值格式化字符串

cell.CheckValue.text = [NSString stringWithFormat:@"%@",_CheckValue[row]]

Answer 3

UIlabel显示的对象是classNSString，你传入的参数是NSDecimalNumber，当你设置文本时检查传入的值包括长度（Lenght方法）因为对象不支持这个方法——报错是抛出。解决方案 - 将 NSDecimalNumber 转换为 NSString。例如：

cell.CheckValue.text = [_CheckValue[row] stringValue];

[NSDecimalNumber Length]：发送到实例的无法识别的选择器

[NSDecimalNumber Length]:unrecognized selector sent to instance

objective-c

unrecognized-selector

nsdecimalnumber