Simple .NET/ASP.NET PDF document editor web control SDK

We re now using the GetString method on our Encoding objects, to decode the byte array back into a string. Here s the output:

UTF-8 ----195 137 99 111 117 116 101 45 109 111 105 33 ASCII ----63 99 111 117 116 101 45 109 111 105 33 Decoded UTF-8 ------------ coute-moi! Decoded ASCII ------------ coute-moi!

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Deleting a record is similar If the data source is ready, you can invoke the deleteCurrentItem method on the parent ItemView control You control access to the button (and thus the deletion) by disabling the button when the dataSource isn t ready: <button targetElement="delButton"> <bindings> <binding dataContext="dataSource" dataPath="isReady" property="enabled"/> </bindings> <click> <invokeMethod target="detailsView" method="deleteCurrentItem" /> </click> </button> Saving data is a little more complex You should save data only when the dataset is considered dirty and the dataSource is considered ready Remember that the binding is two-way, so when you type something into either of the text boxes, their binding to the itemView will update the dataset within the itemView, and it, in turn, will update the dataset within the dataSource control Thus, the dataSource will be considered dirty Once it is also ready, then the isDirtyAndReady flag will be true.

The UTF-8 bytes have decoded back to our original string. This is because the UTF-8 encoding supports the E-acute character, and it does so by inserting two bytes into the array: 195 137. On the other hand, our ASCII bytes have been decoded and we see that the first character has become a question mark. If you look at the encoded bytes, you ll see that the first byte is 63, which (if you look it up in an ASCII table somewhere) corresponds to the question mark character. So this isn t the fault of the decoder. The encoder, when faced with a character it didn t understand, inserted a question mark.

Note You can use a question mark ( ) as a placeholder and then bind values to it from left to right using

So, you need to be careful that any encoding you choose is capable of supporting the characters you are using (or be prepared for the information loss if it doesn t).

OK, we ve seen an example of the one-byte-per-character ASCII representation, and the at-least-one-byte-per-character UTF-8 representation. Let s have a look at the underlying at-least-two-bytes-per-character UTF-16 encoding that the framework uses internally Example 10-83 uses this.

static void Main(string[] args) { string listenUpFR = " coute-moi!"; byte[] utf16Bytes = Encoding.Unicode.GetBytes(listenUpFR); Console.WriteLine("UTF-16"); Console.WriteLine("-----"); foreach (var encodedByte in utf16Bytes) {

} }

addBindValue(QVariant). I recommend against this procedure because it is far easier to alter and far less

Console.Write(encodedByte); Console.Write(" ");

You can bind the enablement of the Save button to this flag, and you will then be protected from bad writes Thus, when the dataSource is dirty and it is ready for writing, the button will be enabled; otherwise, it will be disabled and unavailable for user interaction When you click the button, the action to update the dataSource should take place <button targetElement="saveButton"> <bindings> <binding dataContext="dataSource" dataPath="isDirtyAndReady" property="enabled"/> </bindings> <click> <invokeMethod target="dataSource" method="update" /> </click> </button> Refreshing the data involves running another query on the data source to perform another select and get a refreshed dataset This should happen only when the dataSource is ready to receive the request Thus, you bind the enablement of the button to the isReady property of the dataSource, and when you click it, you invoke the select method to get the data.

Console.ReadKey();

Notice that we re using the Unicode encoding this time. If we compile and run, we see the following output:

Listing 13-5. Binding values to a query containing an INSERT call qry.prepare( "INSERT INTO names (id, firstname, lastname) " "VALUES (:id, :firstname, :lastname)" ); qry.bindValue( ":id", 9 ); qry.bindValue( ":firstname", "Ralph" ); qry.bindValue( ":lastname", "Roe" ); if( !qry.exec() ) qDebug() << qry.lastError();

UTF-16 ----201 0 99 0 111 0 117 0 116 0 101 0 45 0 109 0 111 0 105 0 33 0

It is interesting to compare this with the ASCII output we had before:

ASCII ----63 99 111 117 116 101 45 109 111 105 33

If you need to use several database connections at once, you have to name them. If the connection name is not specified, the default connection is always used. If a new connection is established using the same name as a previous connection, it will replace the previous connection. This goes for the default connection as well. When you add the connection using QSqlDatabase::addDatabase(QString,QString), the first parameter is the name of the database driver (for example, QMYSQL),while the second optional parameter is the name of the connection. When creating your QSqlQuery object, you can pass a database object to the constructor if you want it to use a specific connection. If you need to retrieve the QSqlDatabase object for a connection name, you can use the static QSqlDatabase::database(QString) method.