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

This is pretty similar to the foreach example. It s marginally shorter, but it s also a little more awkward our program is counting the laps starting from 1, but arrays in .NET start from zero, so the line that parses the value from the file has the slightly ungainly expression lines[lapNumber - 1] in it. (Incidentally, this example avoids using a short iteration variable name such as i because we re numbering the laps from 1, not 0 short iteration variable names tend to be associated with zero-based counting.) Arguably, the foreach version was clearer, even if it was ever so slightly longer. The main

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First the group box is added; then a spacer is added The spacer is not added as a widget; in fact, there is no spacer widget By calling the addStretch method, a QSpacerItem is inserted into the layout This item works as a spacer, so the effect is the same as when you used Designer Finally buttons are added to the bottom of the layout Listing 3-2 The widgets are laid out QHBoxLayout *hLayout = new QHBoxLayout( groupBox ); hLayout->addWidget( label ); hLayout->addWidget( lineEdit ); QVBoxLayout *vLayout = new QVBoxLayout( &dlg ); vLayout->addWidget( groupBox ); vLayout->addStretch(); vLayout->addWidget( buttons ); Both listings result in the dialog shown in Figure 3-4 If you want to play with the layout policies from the code, you need to know which properties and methods to use All widgets have a sizePolicy property, which is represented by a QSizePolicy object.

advantage of for is that it doesn t require a collection, so it s better suited to Example 2-14 than Example 2-15.

C# offers a third kind of iteration statement: the while loop. This is like a simplified for loop it has only the Boolean expression that decides whether to carry on looping, and does not have the variable initialization part, or the statement to execute each time around. (Or if you prefer, a for loop is a fancy version of a while loop neither for nor foreach does anything you couldn t achieve with a while loop and a little extra code.) Example 2-16 shows an alternative approach to working through the lines of a text file based on a while loop.

static void Main(string[] args) { using (StreamReader times = File.OpenText("LapTimes.txt")) { while (!times.EndOfStream) { string line = times.ReadLine(); double lapEndTime = double.Parse(line); Console.WriteLine(lapEndTime); } } }

The minimumSize and maximumSize properties are QSize objects..

The Atlas HyperLink control corresponds to an HTML anchor tag, <a>, which can be used to place hyperlinks to external sites or to place internal bookmarks on your page. You define an image tag in your page like this: <a id="Href1" href="http://www.philotic.com/blog">Hyperlink</a>

The while statement is well suited to the one-line-at-a-time approach. It doesn t require a collection; it just loops until the condition becomes false. In this example, that means we loop until the StreamReader tells us we ve reached the end of the file.# ( 11 describes the use of types such as StreamReader in detail.) The exclamation mark (!) in front of the expression means not you can put this in front of any Boolean expression to invert the result. So the loop runs for as long as we are not at the end of the stream.

We could have used a for loop to implement this one-line-at-a-time loop it also iterates until its condition becomes false. The while loop happens to be a better choice here simply because in this example, we have no use for the variable initialization or loop statement offered by for.

#You ll have noticed the using keyword on the line where we get hold of the StreamReader. We use this construct when it s necessary to indicate exactly when we ve finished with an object in this case we need to say when we re done with the file to avoid keeping operating system file handles open.

The approach in Example 2-16 would be better than the previous examples for a particularly large file. The code can start working straight away without having to wait for the entire file to load, and it will use less memory because it doesn t build the array containing every single line it can hold just one line at a time in memory. For our example lap time file with just six lines of data, this won t make any difference, but if you were processing a file with hundreds of thousands of entries, this while-based example could provide noticeably better performance than the array-based examples.

When I refer to a property name, for example sizePolicy, it is understood that there is a getter Tip method called sizePolicy and a setter method called setSizePolicy. There are read-only properties without setter, but they are uncommon.

This does not mean that while is faster than for or foreach. The performance difference here is a result of the code working with the file in a different way, and has nothing to do with the loop construct. In general, it s a bad idea to focus on which language features are fastest. Performance usually depends on the way in which your code solves a problem, rather than which particular language feature you use.