高仿Windows Phone QQ登录界面实例代码

给 TextBox文本框前添加图片

扩展PhoneTextBox:添加一个类“ExtentPhoneTextBox”继承 PhoneTextBox ，在“ExtentPhoneTextBox”类中添加属性项：
代码如下:
public class ExtentPhoneTextBox : PhoneTextBox
    {
        /// <summary>
        /// 文本框图片属性
        /// </summary>
        public static readonly DependencyProperty TextHeadImageProperty =
            DependencyProperty.Register("TextHeadImage", typeof(ImageSource), typeof(ExtentPhoneTextBox), new PropertyMetadata(null)
            );

        /// <summary>
        /// 文本框头图片
        /// </summary>
        public ImageSource TextHeadImage
        {
            get { return base.GetValue(TextHeadImageProperty) as ImageSource; }
            set { base.SetValue(TextHeadImageProperty, value); }
        }

        /// <summary>
        /// 文本图片宽度
        /// </summary>
        public double TextHeadImageWidth
        {
            get { return (double)GetValue(TextHeadImageWidthProperty); }
            set { SetValue(TextHeadImageWidthProperty, value); }
        }

        // Using a DependencyProperty as the backing store for TextHeadImageWidth.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty TextHeadImageWidthProperty =
            DependencyProperty.Register("TextHeadImageWidth", typeof(double), typeof(ExtentPhoneTextBox), new PropertyMetadata(null));

        /// <summary>
        /// 文本图片高度
        /// </summary>
        public double TextHeadImageHeight
        {
            get { return (double)GetValue(TextHeadImageHeightProperty); }