InnerException Property

Exception.InnerException Property


Gets the Exception instance that caused the current exception.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

public Exception InnerException { get; }

Property Value

Type: System.Exception

An object that describes the error that caused the current exception. The InnerException property returns the same value as was passed into the Exception(String, Exception) constructor, or null if the inner exception value was not supplied to the constructor. This property is read-only.

When an exception X is thrown as a direct result of a previous exception Y, the InnerException property of X should contain a reference to Y.

Use the InnerException property to obtain the set of exceptions that led to the current exception.

You can create a new exception that catches an earlier exception. The code that handles the second exception can make use of the additional information from the earlier exception to handle the error more appropriately.

Suppose that there is a function that reads a file and formats the data from that file. In this example, as the code tries to read the file, an IOException is thrown. The function catches the IOException and throws a FileNotFoundException. The IOException could be saved in the InnerException property of the FileNotFoundException, enabling the code that catches the FileNotFoundException to examine the cause of the initial error.

The InnerException property, which holds a reference to the inner exception, is set upon initialization of the exception object.

The following example demonstrates throwing and catching an exception that references an inner exception.

using System;
using System.CodeDom;
using System.CodeDom.Compiler;
using System.ComponentModel;
using System.IO;
using System.Windows.Forms;

namespace IndentedTextWriterExample
    public class Form1 : System.Windows.Forms.Form
        private System.Windows.Forms.TextBox textBox1;

        private string CreateMultilevelIndentString()
            // Creates a TextWriter to use as the base output writer.
            System.IO.StringWriter baseTextWriter = new System.IO.StringWriter();            

            // Create an IndentedTextWriter and set the tab string to use 
            // as the indentation string for each indentation level.
            System.CodeDom.Compiler.IndentedTextWriter indentWriter = new IndentedTextWriter(baseTextWriter, "    ");           

            // Sets the indentation level.
            indentWriter.Indent = 0;

            // Output test strings at stepped indentations through a recursive loop method.
            WriteLevel(indentWriter, 0, 5);

            // Return the resulting string from the base StringWriter.
            return baseTextWriter.ToString();

        private void WriteLevel(IndentedTextWriter indentWriter, int level, int totalLevels)
            // Output a test string with a new-line character at the end.
            indentWriter.WriteLine("This is a test phrase. Current indentation level: "+level.ToString());

            // If not yet at the highest recursion level, call this output method for the next level of indentation.
            if( level < totalLevels )
                // Increase the indentation count for the next level of indented output.

                // Call the WriteLevel method to write test output for the next level of indentation.
                WriteLevel(indentWriter, level+1, totalLevels);

                // Restores the indentation count for this level after the recursive branch method has returned.
                // Outputs a string using the WriteLineNoTabs method.
                indentWriter.WriteLineNoTabs("This is a test phrase written with the IndentTextWriter.WriteLineNoTabs method.");

            // Outputs a test string with a new-line character at the end.
            indentWriter.WriteLine("This is a test phrase. Current indentation level: "+level.ToString());           

        private void button1_Click(object sender, System.EventArgs e)
            textBox1.Text = CreateMultilevelIndentString();

        public Form1()
            System.Windows.Forms.Button button1 = new System.Windows.Forms.Button();
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.textBox1.Anchor = ((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom) 
                | System.Windows.Forms.AnchorStyles.Left) 
                | System.Windows.Forms.AnchorStyles.Right)));
            this.textBox1.Location = new System.Drawing.Point(8, 40);
            this.textBox1.Multiline = true;
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(391, 242);
            this.textBox1.TabIndex = 0;
            this.textBox1.Text = "";
            button1.Location = new System.Drawing.Point(11, 8);
            button1.Name = "button1";
            button1.Size = new System.Drawing.Size(229, 23);
            button1.TabIndex = 1;
            button1.Text = "Generate string using IndentedTextWriter";
            button1.Click += new System.EventHandler(this.button1_Click);
            this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
            this.ClientSize = new System.Drawing.Size(407, 287);
            this.Name = "Form1";
            this.Text = "IndentedTextWriter example";

        static void Main() 
            Application.Run(new Form1());

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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