com.badlogic.gdx.ai.fsm.StackStateMachine.java Source code

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/*******************************************************************************
 * Copyright 2011 See AUTHORS file.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/

package com.badlogic.gdx.ai.fsm;

import com.badlogic.gdx.utils.Array;

/** A {@link StateMachine} implementation that keeps track of all previous {@link State}s via a stack. This makes sense for example
 * in case of a hierarchical menu structure where each menu screen is one state and one wants to navigate back to the main menu
 * anytime, via {@link #revertToPreviousState()}.
 * @param <E> is the type of the entity handled by this state machine.
 * @author Daniel Holderbaum */
public class StackStateMachine<E> extends DefaultStateMachine<E> {

    private Array<State<E>> stateStack;

    /** Creates a StackStateMachine for the specified owner.
     * @param owner the owner of the state machine */
    public StackStateMachine(E owner) {
        this(owner, null, null);
    }

    /** Creates a StackStateMachine for the specified owner and initial state.
     * @param owner the owner of the state machine
     * @param initialState the initial state */
    public StackStateMachine(E owner, State<E> initialState) {
        this(owner, initialState, null);
    }

    /** Creates a StackStateMachine for the specified owner, initial state and global state.
     * @param owner the owner of the state machine
     * @param initialState the initial state
     * @param globalState the global state */
    public StackStateMachine(E owner, State<E> initialState, State<E> globalState) {
        super(owner, initialState, globalState);
    }

    @Override
    public void setInitialState(State<E> state) {
        if (stateStack == null) {
            stateStack = new Array<State<E>>();
        }

        this.stateStack.clear();
        this.currentState = state;
    }

    @Override
    public State<E> getCurrentState() {
        return currentState;
    }

    /** Returns the last state of this state machine. That is the high-most state on the internal stack of previous states. */
    @Override
    public State<E> getPreviousState() {
        if (stateStack.size == 0) {
            return null;
        } else {
            return stateStack.peek();
        }
    }

    @Override
    public void changeState(State<E> newState) {
        changeState(newState, true);
    }

    /** Change state back to the previous state. That is the high-most state on the internal stack of previous states. */
    @Override
    public boolean revertToPreviousState() {
        if (stateStack.size == 0) {
            return false;
        }

        State<E> previousState = stateStack.pop();
        changeState(previousState, false);
        return true;
    }

    private void changeState(State<E> newState, boolean pushCurrentStateToStack) {
        if (pushCurrentStateToStack && currentState != null) {
            stateStack.add(currentState);
        }

        // Call the exit method of the existing state
        if (currentState != null)
            currentState.exit(owner);

        // Change state to the new state
        currentState = newState;

        // Call the entry method of the new state
        currentState.enter(owner);
    }

}