C ++ design patterns - Observer pattern Observer

Motivation (Motivation)

• In the software build process, we need to establish a "notice dependencies" for certain objects - an object (target object) changes state, all dependent objects (objects observer) will be notified. If such a dependency too closely, the software will not be well to resist change.
• Using object-oriented technology, this dependence may be weakened, and form a stable dependency. Enabling loosely coupled software architecture.

Schema Definition

One kind of inter-defining the object dependencies many relationship (variation) , so that when an object (the Subject) changes state, all dependent on it are notified and updated automatically. - "Design Patterns" GoF

Structure (Structure)

 

 

Takeaways

• Abstract object-oriented, the Observer pattern so that we can change the target and independently of the observer, so that the dependencies between the two to achieve loosely coupled.
• When the target sends a notification without specifying the viewer, notification (notification information can carry as parameters) are automatically propagated.
• The viewer to decide whether to subscribe to notifications, audience knew nothing about.
• Observer model is based UI framework in the event of a very common design patterns, it is also an important part of the MVC pattern.

 The progress bar under Windows Linux console are different

class FileSplitter 
{ 
    String m_filePath;
     int m_fileNumber; 
    the ProgressBar * m_progressBar; // 's role: specific notice Controls
     // replace abstract notification mechanism. Transition completed concrete to abstract 
    / * 
    dependent on implementation details, contrary to the design principles dependent inversion principle, layer module should not depend on low-level modules, both should depend on the abstract 
    now to FIG strip into a GUI, if the program control Taiwan program, it indicates that the program schedule by a black dot? 
    * / 

Public : 
    FileSplitter ( const  String & filePath, int filenumber, the ProgressBar * progressBar): 
        m_filePath (filePath), 
        m_fileNumber (filenumber), 
        m_progressBar (progressBar) { 

    } 
    void Split () {

        @ 1 large file read 

        // 2. Small batches write to file 
        for ( int I = 0 ; I <m_fileNumber; I ++ ) {
             // ... 
            a float progressValue = m_fileNumber; 
            progressValue = (I + . 1 ) / progressValue; 
            m_progressBar -> the setValue (progressValue); // update the progress bar 
        } 

    } 
}; 

class the MainForm: public Form1 
{ 
    the TextBox * txtFilePath; 
    the TextBox *  txtFileNumber;
    the ProgressBar* progressBar;//进度条

public:
    void Button1_Click(){

        string filePath = txtFilePath->getText();
        int number = atoi(txtFileNumber->getText().c_str());
        FileSplitter splitter(filePath, number, progressBar);
        splitter.split();
    }
};