TextFiled 控制键盘只可以输入数字（TextFiled only allow number input）

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {

BOOL shouldInput = YES;

NSNumberFormatter * nf = [[NSNumberFormatter alloc] init];
[nf setNumberStyle:NSNumberFormatterDecimalStyle];

NSString * newString = [NSString stringWithFormat:@"%@%@",textField.text,string];
NSNumber * number = [nf numberFromString:newString];

if (number)
shouldInput = YES;
else
shouldInput = NO;

if ([string isEqualToString:@"-"] || !string.length) {
shouldInput = YES;
}

return shouldInput;
}