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POBest way to handle input and state changes for multiple states?
 

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  1. POBest way to handle input and state changes for multiple states?
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    <p>I have an application that has multiple states, with each state responding to input differently.</p> <p>The initial implementation was done with a big switch statement, which I refactored using the state pattern (at least, I think it's the state pattern. I'm kind of new to using design patterns, so I tend to get them confused) -</p> <pre><code>class App { public: static App * getInstance(); void addState(int state_id, AppState * state) { _states[state_id] = state; } void setCurrentState(int state_id) { _current_state = _states[state_id]; } private: App() ~App(); std::map&lt;int, AppState *&gt; _states; AppState * _current_state; static App * _instance; } class AppState { public: virtual void handleInput() = 0; virtual ~AppState(); protected: AppState(); } </code></pre> <p>Currently, each state is polling the OS for input, and acting accordingly. This means each concrete state has a huge switch statement with a case for each valid keypress. Some cases call functions, and other cases issue state changes by using App::setCurrentState(newstate). The catch is that a key that does something in one state may not do anything (or in rare circumstances, may do something different) in another state.</p> <p>Okay, I think that's the pertinent background. Here's the actual question(s) -</p> <p>First, what's the best way to eliminate the huge switch statements in the concrete states? <a href="https://stackoverflow.com/questions/126409/ways-to-eliminate-switch-in-code#126475">This question</a> suggests the command pattern, but I don't understand how I would use it here. Can someone help explain it, or suggest another solution?</p> <p>As a side note, I've considered (and am not opposed to) the idea of letting the App class do the polling of the OS, and then pass inputs to _current_state->handleInput. In fact, something tells me that I'll want to do this as part of the refactoring. I just haven't done it yet.</p> <p>Second, state changes are made by calling App::setCurrentState(newstate). I realize that this is akin to using globals, but I'm not sure of a better way to do it. My main goal is to be able to add states without modifying the App class. Suggestions would be welcome here as well.</p>
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