Introduction:
A couple of days ago I ran into a confusion when I had to decide that whether to use ViewState or Data Caching. The use of ViewState as well as Data Caching technique would have provided me with the correct solution. One of the techniques was better than the other and I had to decide that which one to use. In this article I will discuss when to use ViewState and when to use Caching.
ViewState:
ViewState is one of the techniques that Asp.net provides in order to save the data for latter use. The important fact about the ViewState is that it can only save the values for page level access. It means if I save something on page_1 using Viewstate I cannot access it on the page_2 using the same technique. For this reason ViewState is only used to save the values for the page level access which should be maintained after post backs.
Whenever we write anything in the ViewState object a hidden field is created in the html. Let's see a small example of using viewstate. In this example we will use a TextBox and button. We will write something in the TextBox and press the button to trigger the postback. After the post back we will display the value of the TextBox using the ViewState control.
private void Button1_Click(object sender, System.EventArgs e)
{
if(ViewState["MyValue"] == null)
{
ViewState["MyValue"] = TextBox1.Text;
// Clear the value from the TextBox
TextBox1.Text = "";
}
This is a simple example that shows that how you can use the view state to save the page level values. If you run this and view the source of the page you will notice that the hidden filed is automatically created.
| <input type="hidden" name="__VIEWSTATE" value="dDwtMTY3MTY4OTI3NDs7Pr AYZq+d1r V++f3rE2ngBQMU9l5h" /> |
The value of the hidden field is encrypted but one who knows the encryption can easily decrypt it that's why ViewState is not completely safe. Also the size of your page will increase if you are putting more and more data in the Viewstate control. If you are storing datatable and datasets in ViewState than it will take much longer for the page to execute.
Let's see a small example of storing large objects in the ViewState control.
|
private void Button2_Click(object sender, System.EventArgs e) DataSet ds = new DataSet(); Articles article = new Articles(); ds = article.GetAllArticles(); ViewState["MyArticles"] = ds; } |
This is very simple example that I am using to explain the nightmares of using ViewState control. We are simply making a new dataset object and populating it with the data which is returned from the GetAllArticles method. Finally, we are assigning the dataset to the ViewState control. Run this page and click on the button to write the dataset in the Viewstate and than view the source of the page. You will see something like this:
|
<input type="hidden" name="__VIEWSTATE" value="dDwtMTY3MTY4OTI3NDt0PHA8bDxNeUFydGljbGVzOz47bD xiPEFBRUFBQUQvLy8vL0FRQUFBQUFBQUFBTUFnQUFBRkZUZVhOMFpXMHVSR0YwWV N3Z1ZtVnljMmx2YmoweExqQXVOVEF3TUM0d0xDQkRkV3gwZFhKbFBXNWxkWFJ5WVd3c 0lGQjFZbXhwWTB0bGVWUnZhMlZ1UFdJM04yRTFZelU yTVRrek5HVXdPRGtGQVFBQUFCTl RlWE4wWlcwdVJHRjBZUzVFWVhSaFUyVjBBZ0FBQUFsWWJXeFRZMmhsYldFTFdHMXNS |
And this is just three of the 50-60 lines. So, now you can think that if you are storing large datasets in the ViewState your page size will grow dramatically and hence the page execution as well as page loading will be tremendously slow. For this reason we turn to Data Caching.
Let's see what data caching is all about.
Data Caching:
Caching is one of the coolest features in Asp.net. Caching enables you to store the expensive data into Cache object and later retrieve it without doing expensive operations. Data Caching can tremendously increase performance since each time the data is requested you can turn to the Cache object rather than going to the database and fetching the result.
You all must be familiar with datagrid paging where you can display certain number of records in the datagrid control and use the numeric or next-previous buttons to view the other records. All the records are fetched for each and every page in the datagrid. Meaning that if you have 40000 records in the database and you are using paging. Each time you click to go to the next page you retrieve 40000 records. This is way too much performance kill. That's why for this task we can use Data Caching, let's see how we can use data caching to make our application more efficient.
|
private void Button3_Click(object sender, System.EventArgs e) if(Cache["MyArticles"] == null) // Go to the database and fetch the result in the DataSet // Assign the dataset to the Cache object // Cache["MyArticles"] = ds } // This means that Cache is not empty and there is data in the cache // Extract the value of Cache object to the DataSet // DataSet ds = (DataSet) Cache["MyArticles"] } } |
The above example is pretty much simple and as you have also noticed that the syntax for using Data Caching is very similar to the ViewState object. By using this technique you will only get the data from the database if the Cache is empty. And if you see the page source you will not find any hidden fields since Cache is stored in memory rather than in page source.
Final Thoughts:
When it comes to choosing between ViewState and Caching it all comes down to what you are doing. ViewState is an ideal candidate if you are planning to save small values. Mostly values of server controls are saved in ViewState. If you plan to store large datasets, datatables or collections than data caching is an excellent candidate.
else
{
// Fill the Textbox with the value from ViewState
TextBox1.Text = ViewState["MyValue"].ToString();
}
}
Attachments:
Project Files: ViewStateVsCaching_Sample.zip
