wpf实现焦点进入或点击TextBox选中文字

(一)UI实现代码如下：

<Window x:Class="WpfApplication2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <StackPanel>
            <TextBox Height="23"  Name="textBox1" Width="120" Tag="1" Text="100"  GotFocus="textBox1_GotFocus" LostFocus="textBox1_LostFocus"  PreviewMouseDown="textBox1_PreviewMouseDown" />
            <TextBox Height="23"  Name="textBox2" Width="120" Tag="2" Text="200" GotFocus="textBox1_GotFocus" LostFocus="textBox1_LostFocus"  PreviewMouseDown="textBox1_PreviewMouseDown"  />
            <Button Content="Button" Height="23" Name="button1"  Width="75" />
        </StackPanel>
    </Grid>
</Window>

(二）后台代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApplication2
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        private float value1 = 0f;
        private float value2 = 0f;
        public MainWindow()
        {
            InitializeComponent();
        }   

        private void textBox1_GotFocus(object sender, RoutedEventArgs e)
        {
            if (sender != null)
            {
                TextBox tbx = sender as TextBox;        
                tbx.SelectAll();
                tbx.PreviewMouseDown -= new MouseButtonEventHandler(textBox1_PreviewMouseDown);
               
            }
        }

        private void textBox1_PreviewMouseDown(object sender, MouseButtonEventArgs e)
        {
            TextBox tb = sender as TextBox;
            if (tb != null)
            {
                tb.Focus();
                e.Handled = true;
            }
        }

        private void textBox1_LostFocus(object sender, RoutedEventArgs e)
        {
           
            TextBox tb = sender as TextBox;
            if (tb != null)
            {
                tb.PreviewMouseDown += new MouseButtonEventHandler(textBox1_PreviewMouseDown);
            }
        }
    }
}