C# 属性.设置.默认

Question

How to ensure that retrieving value from Properties.Settings.Default exists? For example, when I use this code:

folderBrowserDialog1.SelectedPath = (string)Properties.Settings.Default["SelectedPath"];

and value SelectedPath does not exist, I get the followng exception:

System.Configuration.SettingsPropertyNotFoundException' occurred in System.dll

How can I avoid this exception?

Answer 1

Here is a method to check for the existence of a key:

    public static bool PropertiesHasKey(string key)
    {
        foreach (SettingsProperty sp in Properties.Settings.Default.Properties)
        {
            if (sp.Name == key)
            {
                return true;
            }
        }
        return false;
    }

Answer 2

Unless that collection provides a method to check whether a given key exists then you will have to wrap the code in a try..catch block.

 try{
     folderBrowserDialog1.SelectedPath = (string)Properties.Settings.Default["SelectedPath"];
 }catch(System.Configuration.SettingsPropertyNotFoundException)
 {
     folderBrowserDialog1.SelectedPath = "";  // or whatever is appropriate in your case
 }

If the Default property implements the IDictionary interface you can use the ContainsKey method to test that the given key exists before trying to access it, like so:

 if(Properties.Settings.Default.ContainsKey("SelectedPath"))
 {
     folderBrowserDialog1.SelectedPath = (string)Properties.Settings.Default["SelectedPath"];
 }else{
     folderBrowserDialog1.SelectedPath = ""; // or whatever else is appropriate in your case
 }

Answer 3

try this:(our friend 'Mike Dinescu' mention that with no details - Edit: he has provided details now)

try
{
    folderBrowserDialog1.SelectedPath = 
     (string)Properties.Settings.Default["SelectedPath"]
}
catch(System.Configuration.SettingsPropertyNotFoundException e)
{
    MessageBox.Show(e.Message); // or anything you want
}
catch(Exception e)
{
    //if any exception but above one occurs this part will execute
}

I hope this solution solve your problem :)

Edit : Or without using try catch :

if(!String.IsNullOrEmpty((string)Properties.Settings.Default["SelectedPath"]))
{
   folderBrowserDialog1.SelectedPath = 
         (string)Properties.Settings.Default["SelectedPath"]
}

Answer 4

you can set default null value for the variable . add this code to Settings.Designer.cs file :

[UserScopedSetting]
[DebuggerNonUserCode]
[DefaultSettingValue(null)] // <-- set default value
public string test1
{
    get
    {
        return (string)this[nameof(test1)];
    }
    set
    {
        this[nameof(test1)] = (object)value;
    }
} 

then check :

if (Properties.Settings.Default.test1 != null)