blocks|key|3123494|text|可以将旧值存储在try块之外的变量解密中，并在catch块中再次使用该变量：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3123495|string+oldSumValue+=+tbxSum.Text;

try
{
++++//+your+code++++++++++
}
catch
{
++++tbxSum.Text+=+oldSumValue+;
++++MessageBox.Show("Invalid+Sum");+++++++
}|code-block|syntax|javascript|3123496|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can store the old value in a variable declard outside the try block and use this variable in your catch block again:

<pre><code>string oldSumValue = tbxSum.Text;

try
{
 // your code 
}
catch
{
 tbxSum.Text = oldSumValue ;
 MessageBox.Show("Invalid Sum"); 
}
</code></pre>

blocks|key|2262961|text|class+Calculate(){
++++private+boolean+lastGoodValueSet+=+false;
++++private+int+lastGoodValue+=+0;

++++void+buttonFunction(){
++++++++if+(myButton.Content.ToString()+==+"=")
++++++++{
++++++++++++//Your+code
++++++++++++try
++++++++++++{
++++++++++++++++var+v+=+dt.Compute(s,+"");
++++++++++++++++tbkSum.Text+=+s+%2B+"="+%2B+v.ToString();
++++++++++++++++lastGoodValue+=+v;
++++++++++++++++lastGoodValueSet+=+true;
++++++++++++}

++++++++++++catch
++++++++++++{+++
++++++++++++++++MessageBox.Show("Invalid+Sum");
++++++++++++++++tbxSum.Text+=+result;
++++++++++++++++if+(lastGoodValueSet)
++++++++++++++++++++tbxSum.Text+=+lastGoodValue;
++++++++++++}
++++++++}
++++}

}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2262962|这是一个可以使用的代码示例集，它是一个简单的值，您必须存储它来表示是否已经完成了一个好的计算，如果是这样的话，在错误的地方，我们想回到计算。希望这能帮上忙！您会想要向用户发送某种消息，这样他们就知道有错误了。|unstyled|2262963|我们必须这样做，因为在用户按“等于”按钮时，tbkSum中的值已经发生了变化，在用户更改值之前就需要它，所以获取它的最佳时机是在成功计算时更新tbkSum文本值时。|offset|length|style|CODE|2262964|这也是假设每次计算时都不创建Calculate类的新实例。否则你需要把号码储存在其他地方|2262965|编辑解决此问题的另一种方法是首先防止重复，我从您的其他评论中看到，您可以通过应用程序上的按钮来控制文本框中的内容。假设所有按钮都通过相同的buttonFunction()方法，那么您可以这样做：|BOLD|2262966|private+char[]+buttonChars+=+{'/','*',+'%2B'/*e.t.c*/}
void+buttonFunction(){
++++string+buttonPressedStr+=+myButton.Content.ToString();
++++char+buttonPressed+=+buttonPressedStr[0];
++++int+pos+=+Array.IndexOf(buttonChars+,+buttonPressed);
++++if+(pos+>+-1)
++++{
++++++++if+(tbxSum.Text.Length+>+0){
++++++++++++char+last+=+tbxSum.Text[tbxSum.Text.Length+-+1];
++++++++++++pos+=+Array.IndexOf(buttonChars+,+last);
++++++++}
++++++++else
++++++++++++pos+=+0;
++++++++if+(pos+>+-1){
++++++++++++tbkSum.Text+%2B=+buttonPressedStr;
++++++++}
}|2262967|有更清洁的方法可以做到这一点，但这是一个例子，你可以防止你的问题在第一位。一些解释：|2262968|buttonChars是一个不同按钮类型的数组，将其附加到框中的文本中，例如%2B、-等等。|ordered-list-item|2262969|首先，它检查按下的按钮是否在指定的buttonChars集合中。|2262970|如果是这样的话，我们必须检查最后添加到tbxSum中的是什么|2262971|如果最后添加到tbxSum中的内容再次出现在buttonChars数组中，则不希望追加字符串|2262972|否则，如果tbxSum为空或末尾有另一个字符，则可以追加字符。|2262973|entityMap^0|0|0|M|6|1Z|6|0|E|9|0|0|2|1X|G|0|0|0|0|B|0|H|B|0|J|6|0|7|6|M|B|0|5|6|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|19|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|1A|8|@$I|1B|J|1C|K|L]|$I|1D|J|1E|K|L]]|9|@]|A|$]]|$1|M|3|N|5|F|7|1F|8|@$I|1G|J|1H|K|L]]|9|@]|A|$]]|$1|O|3|P|5|F|7|1I|8|@$I|1J|J|1K|K|Q]|$I|1L|J|1M|K|L]]|9|@]|A|$]]|$1|R|3|S|5|6|7|1N|8|@]|9|@]|A|$B|C]]|$1|T|3|U|5|F|7|1O|8|@]|9|@]|A|$]]|$1|V|3|W|5|X|7|1P|8|@$I|1Q|J|1R|K|L]]|9|@]|A|$]]|$1|Y|3|Z|5|X|7|1S|8|@$I|1T|J|1U|K|L]]|9|@]|A|$]]|$1|10|3|11|5|X|7|1V|8|@$I|1W|J|1X|K|L]]|9|@]|A|$]]|$1|12|3|13|5|X|7|1Y|8|@$I|1Z|J|20|K|L]|$I|21|J|22|K|L]]|9|@]|A|$]]|$1|14|3|15|5|X|7|23|8|@$I|24|J|25|K|L]]|9|@]|A|$]]|$1|16|3|-4|5|F|7|26|8|@]|9|@]|A|$]]]|17|$]]

<pre><code>class Calculate(){
 private boolean lastGoodValueSet = false;
 private int lastGoodValue = 0;

 void buttonFunction(){
 if (myButton.Content.ToString() == "=")
 {
 //Your code
 try
 {
 var v = dt.Compute(s, "");
 tbkSum.Text = s + "=" + v.ToString();
 lastGoodValue = v;
 lastGoodValueSet = true;
 }

 catch
 { 
 MessageBox.Show("Invalid Sum");
 tbxSum.Text = result;
 if (lastGoodValueSet)
 tbxSum.Text = lastGoodValue;
 }
 }
 }

}
</code></pre>

This is an example set of code you could use, it's a simple value that you have to store to say if a good computation has been done and if so, at the point of error we want to go back to the computation. Hope that helps! You'll want to put some kind of message to the user, so they know there was an error though.

We have to do this, as at the point of the user pressing the equals button, the value has already changed inside <code>tbkSum</code>, we need it before the user has changed the value, so the best time to grab it is at the point when we update the <code>tbkSum</code> text value at a successful calculation

This is also assuming you do not create a new instance of the <code>Calculate</code> class each time you do your computation. Otherwise you'd need to store the number somewhere else

EDIT
The other way to fix this issue is to instead prevent the duplicate in the first place, I read from your other comments that you control what goes into the text box by buttons on the application. Assuming all buttons go through the same method of <code>buttonFunction()</code> then you could do:

<pre><code>private char[] buttonChars = {'/','*', '+'/*e.t.c*/}
void buttonFunction(){
 string buttonPressedStr = myButton.Content.ToString();
 char buttonPressed = buttonPressedStr[0];
 int pos = Array.IndexOf(buttonChars , buttonPressed);
 if (pos &gt; -1)
 {
 if (tbxSum.Text.Length &gt; 0){
 char last = tbxSum.Text[tbxSum.Text.Length - 1];
 pos = Array.IndexOf(buttonChars , last);
 }
 else
 pos = 0;
 if (pos &gt; -1){
 tbkSum.Text += buttonPressedStr;
 }
}
</code></pre>

There are cleaner ways to do this, but it's an example of how you could have prevented your issue in the first place. Some explanation:

<ol>
<li><code>buttonChars</code> is an array of your different button types that would be appended to your text in the box, an example is +, -, and so on</li>
<li>First it checks if the button pressed was in your collection of specified <code>buttonChars</code></li>
<li>If so, we have to check what the last thing added to the <code>tbxSum</code> was</li>
<li>If the last thing added to <code>tbxSum</code> was again found in the <code>buttonChars</code> array, we don't want to append a string</li>
<li>Otherwise, if the <code>tbxSum</code> was empty or had another character at the end, we can append our character</li>
</ol>

blocks|key|2263008|text|或者，我想出了这个方法来防止这样的情况发生：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2263009|A)“*”或“/”的副本|2263010|(B)以'*‘或'/’开头的总和|2263011|public+MainWindow()
++++{
++++++++InitializeComponent();

++++++++if+(tbxSum.Text+==+"")
++++++++{
++++++++++++btnDiv.IsEnabled+=+false;
++++++++++++btnMult.IsEnabled+=+false;
++++++++}
++++}

++++protected+void+btnSumClick(object+sender,+EventArgs+e)
++++{

++++++++btnDiv.IsEnabled+=+true;
++++++++btnMult.IsEnabled+=+true;

++++++++var+myButton+=+(Button)sender;
++++++++int+pos+=+tbxSum.Text.Length;

++++++++if+(pos+>+0)
++++++++{

++++++++++++if+((tbxSum.Text[pos+-+1]+==+'/'+%7C%7C+tbxSum.Text[pos+-+1]+==+'*')+&&
++++++++++++++++(myButton.Content.ToString()+==+"/"+%7C%7C+myButton.Content.ToString()+==+"*"))
++++++++++++{
++++++++++++++++int+location+=+tbxSum.Text.Length+-+1;
++++++++++++++++tbxSum.Text+=+tbxSum.Text.Remove(location,+1);
++++++++++++}

++++++++}
++++}|code-block|syntax|javascript|2263012|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|P|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Alternatively I've come up with this to prevent there being:

A)Duplicate of '*' or '/'

B)Sum starting with '*' or '/'

<pre><code>public MainWindow()
 {
 InitializeComponent();

 if (tbxSum.Text == "")
 {
 btnDiv.IsEnabled = false;
 btnMult.IsEnabled = false;
 }
 }

 protected void btnSumClick(object sender, EventArgs e)
 {

 btnDiv.IsEnabled = true;
 btnMult.IsEnabled = true;

 var myButton = (Button)sender;
 int pos = tbxSum.Text.Length;

 if (pos &gt; 0)
 {

 if ((tbxSum.Text[pos - 1] == '/' || tbxSum.Text[pos - 1] == '*') &amp;&amp;
 (myButton.Content.ToString() == "/" || myButton.Content.ToString() == "*"))
 {
 int location = tbxSum.Text.Length - 1;
 tbxSum.Text = tbxSum.Text.Remove(location, 1);
 }

 }
 }
</code></pre>

So I've just been making a basic little calculator made up of buttons and a textbox(tbxSum). 

The problem I'm having is that if an invalid sum is input I want my catch block to pick it up(which it does) and replace what's in the textbox with the most recent result in the calculator(which it doesn't).

So say I say:

3+3=6

My calculator will now put 6 in the textbox for the next sum.

So then say I did:

6//3

It's invalid which the calculator picks up, but I want the textbox value to return to 6 from the previous sum.

This is what I've tried: 

<pre><code>var myButton = (Button)sender;

 if (myButton.Content.ToString() == "=")
 {

 DataTable dt = new DataTable();
 string s = tbxSum.Text;
 string result = "";

 if (s.Contains("("))
 {
 s = s.Replace("(", "*(");
 }

 try
 {
 var v = dt.Compute(s, "");
 tbkSum.Text = s + "=" + v.ToString();

 tbxSum.Text = v.ToString();
 }

 catch
 { 
 MessageBox.Show("Invalid Sum");
 tbxSum.Text = result;
 }
 }
</code></pre>

I also have a textblock(tbkSum) which shows the previous sum so I thought maybe I could take everything in there to the right of the equals sign but I have no idea how to do that.

Is there a way to use a variable in a catch block that was previously assigned in a try block?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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所以我刚刚做了一个由按钮和文本框(TbxSum)组成的基本计算器。我遇到的问题是，如果输入了无效的和，我希望我的catch块取起它(确实如此)，并将文本框中的内容替换为计算器中的最新结果(它没有)。所以我说：3+3=6现在，我的计算器将把6放在文本框中，用于下一次和。所以说我做了：6/3计算器拾取的内容无效，但我希望文...

问是否有一种方法可以在catch块中使用以前在try块中分配的变量？
EN

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问是否有一种方法可以在catch块中使用以前在try块中分配的变量？EN