Immediate window in .NET framework

Generate QR Code JIS X 0510 in .NET framework Immediate window

The Immediate window allows you to type almost any variable, property, or expression and immediately see its value.

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8: Errors, Exceptions, and Bugs, Oh My!

To see the value of an expression, prepend it with a question mark. For instance, if the breakpoint is on the line shown in Figure 8-13, you will see the value of the integer i by entering the following line:

i

in the Immediate window and pressing Enter. Figure 8-15 shows the result of that exercise; additionally, this figure shows the process of assigning a new value to the variable i and then viewing its value again. If you change the value of a variable in the Immediate window and then continue to run the program, the new value will now be in effect. You can clear the contents of the Immediate window by right-clicking anywhere in the window and selecting Clear All. Close the window by clicking the X in the upperright corner. If you close the window and subsequently bring it back up in the same session, it will still have all the previous contents.

The Locals window shows all the variables local to the current context displayed in a hierarchical table. A typical Locals window is shown in Figure 8-16.

There are columns for the name of the object, its value, and its type. A plus sign next to an object indicates that it has child objects that are not displayed, while a minus sign indicates that its child objects are visible. Clicking a plus symbol drills down the tree and shows any children, while clicking a minus symbol contracts the tree and displays only the parent. A very useful feature is that values that change in the current step display in red. You can select and edit the value of any variable. The value will display as red in the Locals window. Any changes to values take effect immediately.

The Watch window is the same as the Locals window, except that it shows only variables, properties, or expressions you enter into the Name field in the window or drag from another window. The biggest advantage of using a Watch window is that it allows you to decide exactly which objects you want to watch.

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8: Errors, Exceptions, and Bugs, Oh My!

In addition to typing in the name of the object you want to watch, you can also drag and drop variables, properties, or expressions from a code window. Select the object in the code you want to put in the Watch window and then drag it to the Name field in the open Watch window. You can also drag and drop objects from the Locals windows into the Watch window. To do so, both the source window and the Watch window must be open. Highlight a line in the Locals window and drag it down over the Watch tab. The Watch window will come to the foreground. Continue dragging the object to an empty line in the Watch window.

The Call Stack window displays the names of the methods on the call stack and their parameter types and values. You can control which information is displayed in the Call Stack window by right-clicking anywhere in the window and toggling field names that appear in the lower portion of the pop-up menu.

You can and should avoid bugs, but there are runtime errors that cannot be avoided and should be handled as gracefully as possible. You would like to avoid having the end user see ugly or cryptic error messages, or worse, having the application crash. Errors can arise from any number of causes: user action, such as entering invalidly formatted text into a field, program logic errors, or circumstances entirely out of your control, such as an unavailable file or a downed network. The simplest bugs to find and fix are syntax errors: violations of the rules of the language. For example, suppose you had the following line of code in your VB program: