Unable to cast object of type 'System.String' to type 'System.Byte[]'

Question

I am saving Image in a database in a wpf App. but when i retrieve it it gives me type cast error.

Unable to cast object of type 'System.String' to type 'System.Byte[]'.

i am using following code to type cast

byte[] data = (byte[])ds.Tables[0].Rows[0]["ProjectIcons"];

Well presumably the type of the `ProjectItems` column is `String` instead of `byte[]`... Either your database is using the wrong column type, or you're using the wrong type when fetching it. We need more context. — Jon Skeet, Jun 06 '14 at 12:06
@HarjeetSingh: take a look at this: http://stackoverflow.com/questions/4900605/sql-server-varbinarymax-to-c-sharp-byte — HABJAN, Jun 06 '14 at 12:09

score 1 · Answer 1 · answered Jun 06 '14 at 12:44

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In order to convert from string to byte[], you need to specify the encoding. Using UTF-8, it'd be:

byte [] stringArray = Encoding.UTF8.GetBytes("aaa");

Keep in mind that the same character may be represented by different number and value of bytes, so depending on what you need it for, you'll have to use the right encoding.

answered Jun 06 '14 at 12:44

Caótico fanegas

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Thanks @Caótico fanegas , How may i check the format? means coded format , so i will encode it – Harjeet Singh Jun 06 '14 at 12:46
Somehow, @HarjeetSingh, `ds.Tables[0].Rows[0]["ProjectIcons"]`is returning a string, use the Visual Studio Inspector and breakpoints to consult the actual type and value of that datatable field. Also, what's the database type of that field? – Caótico fanegas Jun 06 '14 at 12:50
i inspect it. it has System.Byte[] in its Value and Object{string} in its Type. Datatype in db is varBinary(max) , i also tried with Type image – Harjeet Singh Jun 06 '14 at 12:59

Systematix Infotech · Answer 2 · 2014-06-07T11:21:39.283

0

Try this

string s = (string)ds.Tables[0].Rows[0]["ProjectIcons"];
byte[] data = System.Text.Encoding.ASCII.GetBytes(s);

edited Jun 07 '14 at 11:21

answered Jun 06 '14 at 12:09

Systematix Infotech

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this gives me an error "Unknown method GetBytes(Object) of System.Text.UTF8Encoding" – Harjeet Singh Jun 06 '14 at 12:12
@ Systematix Infotech this is not working... I have already checked this – Harjeet Singh Jun 06 '14 at 12:20
It is already asked by one user at top. btw its varBinary(max) – Harjeet Singh Jun 06 '14 at 12:35
If possible change it to image and then try – Systematix Infotech Jun 06 '14 at 12:37
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Harjeet, let's try some basic problem-solving. Did you look up the GetBytes() method in MSDN? Did you discover that it can take a String argument, or an argument of several other possible types due to overloading? Did you think about the data type of that expression that's being read as an Object in your code? Did you think about how to fix that problem? – catfood Jun 06 '14 at 12:46
this gives me an error "Unknown method GetBytes(Object) – Harjeet Singh Jun 06 '14 at 13:05

Unable to cast object of type 'System.String' to type 'System.Byte[]'

2 Answers2