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Bücher,C undC#TrainingsfürProgrammierer c schulungen, C# Schulungen, Bücher über c mit Visual Studio
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| bet | 3/8 | | Sana | 20.02.2024 | | Hajmi | 1,28 Mb. | | #159175 |
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The control that was clicked last on a form (or in the pull-down menu of the Properties window) is called the currently selected control. You can identify it by the small squares on its edges, the so-called drag handles. You can drag them with the mouse to change to resize the control. A form becomes the currently selected control by clicking on a free position in the form.
Example: In the last example, button1 is the currently selected control.
In the Properties window (context menu of the control on the form, or View|Properties window – do not confuse with View|Property pages).
the properties of the currently selected control are displayed. The left column contains the names and the right column contains the values of the properties. With F1 you get a description of the property.
The value of a property can be changed via the right column. For some properties, you can type the new value using the keyboard. For others, after clicking on the right column, a small triangle is displayed for a pull-down menu, through which a value can be selected. Or an icon with three dots „…“ is displayed, which can be used to enter values.
Example:
For the Text property, you can enter a text with the keyboard. For a button this text is the inscription on the button (e.g. „OK“), and for a form the title line (e.g. „My first C program“).
For the BackColor property (e.g. from a button) you can select the background color via a pull-down menu.
If you click the right column of the Font property and then the „…“ icon, you can select the font of the Text property.
A control on the form is not only adjusted to its properties in the Properties panel, but also vice versa: if you resize it by dragging the drag handles on the form, the values of the corresponding properties (Location and Size in the Layout section) in the Properties panel are automatically updated.
First steps in C++
Next, the program from Section 1.5 is to be extended so that instructions are executed in response to user input (e.g., a button click).
Windows programs can receive user input in the form of mouse clicks or keyboard input. All inputs are received centrally by Windows and passed on to the program. This triggers a so-called event in the program.
Such an event can be assigned a function that is called when the event occurs. This function is also called an event handler.
For the time being, our program should only react to the clicking of a button. The easiest way to get the function called for this event is to double-click on the button in the form. The cursor is then placed at the beginning of the function. This causes Visual Studio to generate the following function and display it in the editor:
Between the curly brackets „{“ and „}“ you then write the statements to be executed when the Click event occurs.
Essentially all instructions of C are possible here. In the context of this simple tutorial, only some elementary instructions are to be introduced, which is necessary for the basic understanding of Visual Studio. If terms like „variables“ etc. are new to you, read on anyway – from the context you will surely get an intuitive idea which is sufficient for the time being.
A frequently used instruction in programming is the assignment (with the operator „=“), which is used to assign a value to a variable. Initially, only those properties of controls that are also displayed in the properties window are to be used as variables. These variables can then be assigned the values that are also offered in the properties window in the right column of the properties.
For the BackColor property, the allowed values are offered after the pulldown menu is expanded:
These values can be used in the program by specifying them after Color::. If you now write the statement
textBox1->BackColor = Color::Yellow;
between the curly brackets
private: System::Void button1_Click(System::Object^ sender, System::EventArgs^ e)
{ textBox1->BackColor = Color::Yellow;
}
the BackColor property of textBox1 gets the value Color::Yellow, which stands for the color yellow, when button1 is clicked during the execution of the program. If you now start the program with F5 and then click button1, the TextBox actually gets the background color yellow.
Even if this program is not yet much more useful than the first one, you have seen how Visual Studio is used to develop applications for Windows. This development process always consists of the following activities:
You design the user interface by placing controls from the Toolbox on the form (drag and drop) and adjusting their properties in the Properties window or the layout with the mouse (visual programming).
You write in C the instructions that should be done in response to user input (non-visual programming).
You start the program and test whether it really behaves as it should.
The period of program development (activities 1. and 2.) is called design time. In contrast, the time during which a program runs is called the runtime of a program.
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