格式化浮动以进行显示时，限制小数位数和总位数

4 回答

• 0

  您正在寻找"maximum significant digits"和"maximum fraction digits"的组合，以及特定的舍入行为 . NSNumberFormatter 等于任务：

  float twofortythreetwentyfive = 234.25;
  float onetwothreefourtwentyfive = 1234.25;
  float eleventwothreefourtwentyfive = 11234.25;
  
  NSNumberFormatter * formatter =  [[NSNumberFormatter alloc] init];
  [formatter setUsesSignificantDigits:YES];
  [formatter setMaximumSignificantDigits:5];
  [formatter setMaximumFractionDigits:2];
  [formatter setRoundingMode:NSNumberFormatterRoundCeiling];
  
  NSLog(@"%@", [formatter stringFromNumber:[NSNumber numberWithFloat:twofortythreetwentyfive]]);
  NSLog(@"%@", [formatter stringFromNumber:[NSNumber numberWithFloat:onetwothreefourtwentyfive]]);
  NSLog(@"%@", [formatter stringFromNumber:[NSNumber numberWithFloat:eleventwothreefourtwentyfive]]);
  

  结果：

  2012-04-26 16：32：04.481 SignificantDigits [11565：707] 234.25 2012-04-26 16：32：04.482 SignificantDigits [11565：707] 1234.3 2012-04-26 16：32：04.483 SignificantDigits [11565：707 ] 11235

  回复于 2024-04-27T00:33:21+08:00
• 1

  Code :

  #define INTPARTSTR(X) [NSString stringWithFormat:@"%d",(int)X]
  #define DECPARTSTR(X) [NSString stringWithFormat:@"%d",(int)(((float)X-(int)X)*100)]
  
  - (NSString*)formatFloat:(float)f
  {
      NSString* result;
  
      result = [NSString stringWithFormat:@"%.2f",f];
  
      if ([DECPARTSTR(f) isEqualToString:@"0"]) return INTPARTSTR(f);
      if ([INTPARTSTR(f) length]==5) return INTPARTSTR(f);
  
      if ([result length]>5)
      {
          int diff = (int)[result length]-7;
  
          NSString* newResult = @"";
  
          for (int i=0; i<[result length]-diff-1; i++)
              newResult = [newResult stringByAppendingFormat:@"%c",[result characterAtIndex:i]];
  
          return newResult;
      }
  
  
      return result;
  }
  

  ---

  Testing it :

  - (void)awakeFromNib
  {
      NSLog(@"%@",[self formatFloat:234.63]);
      NSLog(@"%@",[self formatFloat:1234.65]);
      NSLog(@"%@",[self formatFloat:11234.65]);
      NSLog(@"%@",[self formatFloat:11234]);
  }
  

  Output :

  2012-04-26 19:27:24.429 newProj[1798:903] 234.63
  2012-04-26 19:27:24.432 newProj[1798:903] 1234.6
  2012-04-26 19:27:24.432 newProj[1798:903] 11234
  2012-04-26 19:27:24.432 newProj[1798:903] 11234
  

  回复于 2024-04-27T00:33:21+08:00
• 13

  以下是我在代码中实现此操作的方法 . 我不知道它有多高效，我希望不错 .

  所以我创建了一个全局的NSNumberFormatter

  NSNumberFormatter* numFormatter;
  

  并在某处初始化它：

  numFormatter=[[NSNumberFormatter alloc]init];
  

  然后我使用以下函数格式化数字：

  - (NSString*)formatFloat:(Float32)number withOptimalDigits:(UInt8)optimalDigits maxDecimals:(UInt8)maxDecimals
  {
      NSString* result;
      UInt8 intDigits=(int)log10f(number)+1;
      NSLog(@"Formatting %.5f with maxDig: %d maxDec: %d intLength: %d",number,optimalDigits,maxDecimals,intDigits);  
  
      numFormatter.maximumFractionDigits=maxDecimals;
      if(intDigits>=optimalDigitis-maxDecimals) {
          numFormatter.usesSignificantDigits=YES;
          numFormatter.maximumSignificantDigits=(intDigits>optimalDigits)?intDigits:optimalDigits;
      } else {
          numFormatter.usesSignificantDigits=NO;
      }
      result = [numFormatter stringFromNumber:[NSNumber numberWithFloat:number]];
  
      return result;
  }
  

  回复于 2024-04-27T00:33:21+08:00
• 0

  在iOS 8上的 NSNumberForamtter 上一起使用 maximumFractionDigits 和 maximumSignificantDigits 时，这是一个错误吗？

  NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
          formatter.maximumFractionDigits = 2;  
          formatter.maximumSignificantDigits = 3;
          NSLog(@"%@", [formatter stringFromNumber:@(0.3333)]); // output 0.333 expected 0.33
  

  如果我只使用 maximumFractionDigits 它工作正常

  NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
          formatter.maximumFractionDigits = 2;
          NSLog(@"%@", [formatter stringFromNumber:@(0.3333)]); // output expected .33
  

  NSNumberFormatter maximumFractionDigits and maximumSignificantDigits bug

  回复于 2024-04-27T00:33:21+08:00