使用try / catch可以做到这一点，所以我不能在try / catch块之外使用变量

Question

I have a code that gets a Product object from a web service. If there is no product, it returns an EntityDoesNotExist exception. I need to handle this.. However, I have a lot of other code that deals with the returned Product , but if this code is not within the try/catch, it doesn't work because Product is basically not defined. Is the only way to make this work to include my other related code within the try/catch? This seems really sloppy.

Code example:

try {
    Product product = catalogContext.GetProduct("CatalogName", "ProductId");

} catch(EntityDoesNotExist e) {
    // Do something here
}

if(dataGridView1.InvokeRequired) {
    // Do something in another thread with product
}

Answer 1

Just declare it outside the try/catch scope.

Product product;
try
{
    product = catalogContext.GetProduct("CatalogName", "ProductId");
}
catch (EntityDoesNotExist e)
{
    product = null;
}

if (dataGridView1.InvokeRequired)
{
    // use product here
}

Answer 2

If an exception was thrown when fetching your product then you don't have a product to act on. It seems that you should be ensuring that you only execute the UI code if you didn't throw an exception. That can be done by moving that code inside the try block:

try
{
    Product product = catalogContext.GetProduct("CatalogName", "ProductId");

    if (dataGridView1.InvokeRequired)
    {
        // Do something in another thread with product
    }
}
catch (EntityDoesNotExist e)
{
    // Do something here
}

Answer 3

Is the only way to make this work to include my other related code within the try/catch?

No. Even though an EntityDoesNotExist exception is thrown if the webservice does not return a Product , you need to declare your local Product variable outside of the try block so that your related code outside of the try block can access it.

Declare product outside of the try{}catch{} :

Product product = null;

try 
{        
    product = catalogContext.GetProduct("CatalogName", "ProductId");    
} 
catch(EntityDoesNotExist e) 
{
    // Do something here
}

if(dataGridView1.InvokeRequired) 
{
    // Do something in another thread with product
}