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Spreadsheet: Graphs and MVC

Spreadsheet: Graphs and MVC. Model, View, Controller is MVC Model stores and updates state of application Example: calculator, what's the state of a GUI-calculator? When model changes it notifies its views appropriately Example: pressing a button on calculator, what happens?

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Spreadsheet: Graphs and MVC

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  1. Spreadsheet: Graphs and MVC • Model, View, Controller is MVC • Model stores and updates state of application • Example: calculator, what's the state of a GUI-calculator? • When model changes it notifies its views appropriately • Example: pressing a button on calculator, what happens? • The controller interprets commands, forwards them appropriately to model (usually not to view) • Example: code for calculator that reacts to button presses • Controller isn't always a separate class, often part of GUI-based view in M/VC • MVC is a fundamental design pattern: solution to a problem at a general level, not specific code per se • Patterns part of new foundation of object-orientation

  2. Spreadsheet Model and graphs • What happens when we enter a number, string, or formula? • Model changes to record new entry in a cell • Propagate change to views • Model changes to incorporate dependent calculations • What about D10 change when B10 changes below? • Graphs: why? • Controller? • View? • Dump command?

  3. Toward a working SSModel subclass • How can we associate expressions with cells? • Effects of the command SET A2 = SUM(B1:B10) • We need to get/set expressions, storage possibilities? • How do we notify views when change occurs? • How can we propagate changes to dependent cells? • What associations made for SET A2 = SUM(B1:B10) ? • Edge from B1 to A2, why? • Edge from A2 to B1, why? • Given a graph, how do we propagate changes to model? • Can we just call View::set for every cell and every view? • Use cell/row/col functions in util.h for help with model code

  4. Handling exceptions • How can we handle unanticipated, but certain to occur errors? • Consider command SET A2 = AVERG(B5:B1) • Errors can occur deep in parsing code (recursive) • Where should error be handled? • C++ and Java use exceptions to indicate exceptional condition. • Errors indicated by throwing exception • Client code catches the exception (or program aborts) • Client try/catch blocks guard against uncaught exceptions • Exceptions in spreadsheet are runtime_error objects • Catch pointer, report using re->what() string

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