bwin亚洲必赢5566手机版WPF TextBox按字节长度限制输入

前两天做一个品类的时候,由于页面没有界定TextBox的输入长度,所以,后台一向报错了,超出数据库最大的长短。

数据库的长短是比照字节来总计的,而且不同的编码格式,汉字占用的字节长度又不一样,比如,大家用的是UTF8,一个中国字是3个字节,而默认的Default,一个汉字是2个字节。

TextBox有个马克斯(Max)Length属性,但是那多少个特性是不太相符要求的,因为这多少个长度,是限量了输入的尺寸,比如设置20,则无论数字、字母、汉字最大的长短都是20个,可是,对于数据库来说,长度却不同等了,

就此,无法运用这些特性。

为了,统一解决下这么些问题,所以给TextBox写了增大属性。

 

一、想要的意义

用了增大属性,想达到一个哪些效劳呢,就是像设置马克斯Length一样,一旦到了数据库的字节长度,就不再能输入了。

因而,最开端想找一个范围输入的性能,可惜我学的太浅薄,没有找到有关的性质,因而,最终在同事的唤起下,可以记录上两回的始末,然后,假若超长,就用上五次的内容举办赋值

bwin亚洲必赢5566手机版 1

bwin亚洲必赢5566手机版 2

二、附加属性

既是要用附加属性,并且方便使用,这肯定要给开发者表透露来至少七个:马克斯ByteLength用来安装最大的字节数,EncodeModel用来设置编码格式

EncodeModel是用Menu类型来做的,方便使用时直接敲内容

bwin亚洲必赢5566手机版 3

理所当然上边是平昔想用Encoding来做的,奈何它是抽象类,只可以,写个办法开展了一部转化,并且把Encoding类型的性能举办private。

 

大概上也就是这样一个思路,下边上代码,给急需的人利用。 

public class MaxByteAttachedProperty : DependencyObject
    {
        public enum Encode
        {
            Default,
            ASCII,
            UTF8,
            UTF32,
            UTF7,
            BigEndianUnicode,
            Unicode
        }


        private static string GetPreText(DependencyObject obj)
        {
            return (string)obj.GetValue(PreTextProperty);
        }

        private static void SetPreText(DependencyObject obj, string value)
        {
            obj.SetValue(PreTextProperty, value);
        }

        // Using a DependencyProperty as the backing store for PreText.  This enables animation, styling, binding, etc...
        private static readonly DependencyProperty PreTextProperty =
            DependencyProperty.RegisterAttached("PreText", typeof(string), typeof(MaxByteAttachedProperty), new PropertyMetadata(""));


        public static int GetMaxByteLength(DependencyObject obj)
        {
            return (int)obj.GetValue(MaxByteLengthProperty);
        }

        public static void SetMaxByteLength(DependencyObject obj, int value)
        {
            obj.SetValue(MaxByteLengthProperty, value);
        }

        // Using a DependencyProperty as the backing store for MaxByteLength.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty MaxByteLengthProperty =
            DependencyProperty.RegisterAttached("MaxByteLength", typeof(int), typeof(MaxByteAttachedProperty), new PropertyMetadata(OnTextBoxPropertyChanged));

        private static void OnTextBoxPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            TextBox tb = d as TextBox;
            if (tb == null)
            {
                return;
            }
            tb.PreviewTextInput += Tb_PreviewTextInput;
        }
        private static void Tb_PreviewTextInput(object sender, TextCompositionEventArgs e)
        {
            TextBox tb = sender as TextBox;
            if (IsOutMaxByteLength(tb.Text, tb))
            {
                tb.Text = GetPreText(tb);
                tb.Select(tb.Text.Length, 0);
                return;
            }
        }
        public static Encode GetEncodeModel(DependencyObject obj)
        {
            return (Encode)obj.GetValue(EncodeModelProperty);
        }

        public static void SetEncodeModel(DependencyObject obj, Encode value)
        {
            obj.SetValue(EncodeModelProperty, value);
        }

        // Using a DependencyProperty as the backing store for EncodeM.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty EncodeModelProperty =
            DependencyProperty.RegisterAttached("EncodeModel", typeof(Encode), typeof(MaxByteAttachedProperty), new PropertyMetadata(Encode.UTF8, OnEncodeModelChanged));
        private static void OnEncodeModelChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            SetEM(d, GetEncodeModel(d));
        }

        private static Encoding GetEncodingModel(DependencyObject obj)
        {
            return (Encoding)obj.GetValue(EncodingModelProperty);
        }

        private static void SetEncodingModel(DependencyObject obj, Encoding value)
        {
            obj.SetValue(EncodingModelProperty, value);
        }

        // Using a DependencyProperty as the backing store for EncodingModel.  This enables animation, styling, binding, etc...
        private static readonly DependencyProperty EncodingModelProperty =
            DependencyProperty.RegisterAttached("EncodingModel", typeof(Encoding), typeof(MaxByteAttachedProperty), new PropertyMetadata(Encoding.UTF8));

        private static void SetEM(DependencyObject obj, Encode e)
        {
            switch (e)
            {
                case Encode.Default:
                    SetEncodingModel(obj, Encoding.Default);
                    break;
                case Encode.ASCII:
                    SetEncodingModel(obj, Encoding.ASCII);
                    break;
                case Encode.UTF8:
                    SetEncodingModel(obj, Encoding.UTF8);
                    break;
                case Encode.UTF32:
                    SetEncodingModel(obj, Encoding.UTF32);
                    break;
                case Encode.UTF7:
                    SetEncodingModel(obj, Encoding.UTF7);
                    break;
                case Encode.BigEndianUnicode:
                    SetEncodingModel(obj, Encoding.BigEndianUnicode);
                    break;
                case Encode.Unicode:
                    SetEncodingModel(obj, Encoding.Unicode);
                    break;
                default:
                    break;
            }
        }

        private static bool IsOutMaxByteLength(string txt, DependencyObject obj)
        {
            int txtLength = GetEncodingModel(obj).GetBytes(txt).Length;//文本长度
            if (GetMaxByteLength(obj) >= txtLength)
            {
                SetPreText(obj, txt);
                return false;
            }
            return true;
        }
    }

 

 使用方法如下:

bwin亚洲必赢5566手机版 4

马克斯ByteLength是必须安装的远非展开默认,EncodeModel可以不设置不过由于是我们团结一心用,所以默认是UTF8,可以自动修改代码,按照你们公司的编码格式,这样也就无须赋值了。

 代码已更正,感谢Presia发现的BUG,疏忽了