Android 物理按鍵菜單實現流程

寫在前面，轉載者注：

    該文章主要分析了phonewindow中對expanded Menu處理的流程，介紹的較爲詳細，可供參考。代碼是基於4.1的，同樣適用於4.4。

1. PhoneWindow.onKeyDown() 

     1. onKeyDownPanel.

      當Menu鍵按下去之後，會產生一個KeyEvent，是keyDown事件，如果Activity沒有處理這個Menu Down事件，就會由PhonwWindow默認onKeyDown處理。

在onKeyDown中只要就是調用了onKeyDownPanel把事件傳遞給對應的panel。     

protected boolean onKeyDown(int featureId, int keyCode, KeyEvent event) {

    switch (keyCode) {
        ... ...
        case KeyEvent.KEYCODE_MENU: {
            onKeyDownPanel((featureId < 0) ? FEATURE_OPTIONS_PANEL : featureId, event);
            return true;
        }
        ... ...
    }

    return false;
}

1.1  PhoneWindow.onKeyDownPanel(int featureId, KeyEvent event)

      1. getPanelState()

      根據featureId獲得對應的PanelFeatureState，PanelFeatureState用來保存一個panel對象，比如option menu是對應一個PanelFeatureState 和 featureId。

      2. preparePanel()

       由於是第一次得到PanelFeatureState，st.isOpen返回false，所以就去preparePanel。

public final boolean onKeyDownPanel(int featureId, KeyEvent event) {
    final int keyCode = event.getKeyCode();

    if (event.getRepeatCount() == 0) {
        // The panel key was pushed, so set the chording key
        mPanelChordingKey = keyCode;

        PanelFeatureState st = getPanelState(featureId, true);
        if (!st.isOpen) {
            return preparePanel(st, event);
        }
    }

    return false;
}

1.1.1 PhoneWindow. getPanelState(int featureId, boolean required, PanelFeatureState convertPanelState)

         這個getPanelState也很簡單，如果存在與featureId對應的PanelFeatureState就直接返回，沒有的就new一個新的。也就是如果如果我們再當前Activity中，如果是第一次按menu的話，應該是不存在FEATURE_OPTIONS_PANEL相對應的PanelFeatureState。於是就會new一個新的出來。

private PanelFeatureState getPanelState(int featureId, boolean required,
        PanelFeatureState convertPanelState) {

    PanelFeatureState[] ar;
    if ((ar = mPanels) == null || ar.length <= featureId) {
        PanelFeatureState[] nar = new PanelFeatureState[featureId + 1];
        if (ar != null) {
            System.arraycopy(ar, 0, nar, 0, ar.length);
        }
        mPanels = ar = nar;
    }

    PanelFeatureState st = ar[featureId];
    if (st == null) {
        ar[featureId] = st = (convertPanelState != null)
                ? convertPanelState
                : new PanelFeatureState(featureId);
    }
    return st;
}

1.1.2 PhoneWindow.preparePanel(PanelFeatureState st, KeyEvent event)

        1. 通過Callback（Activity）的onCreatePanelView去創建一個panel，用戶可以複寫這個方法， 如果用戶沒有複寫，則st.createPanelView = null。

        2. initializePanelMenu(), 初始化st中的MenuBuilder，用於以後創建Menu。

        3. 調用cb.onPreparePanel，就會調用Activity的onPreaparePanel方法，而在onPreparePanel中會調用onPrepareOptionsMenu去完成 option menu的prepare工作。完成之後把st中的狀態設置一下。 st.isPrepared = true;   st.isHandled = false;   mPreparedPanel = st;

public final boolean preparePanel(PanelFeatureState st, KeyEvent event) {

    final Callback cb = getCallback();

    if (cb != null) {
        st.createdPanelView = cb.onCreatePanelView(st.featureId);
    }

    if (st.createdPanelView == null) {
        // Init the panel state's menu--return false if init failed
        if (st.menu == null || st.refreshMenuContent) {
            if (st.menu == null) {
                if (!initializePanelMenu(st) || (st.menu == null)) {
                    return false;
                }
            }

            if (mActionBar != null) {
                if (mActionMenuPresenterCallback == null) {
                    mActionMenuPresenterCallback = new ActionMenuPresenterCallback();
                }
                mActionBar.setMenu(st.menu, mActionMenuPresenterCallback);
            }

            st.menu.stopDispatchingItemsChanged();
            st.refreshMenuContent = false;
        }

        // Callback and return if the callback does not want to show the menu

        // Preparing the panel menu can involve a lot of manipulation;
        // don't dispatch change events to presenters until we're done.
        st.menu.stopDispatchingItemsChanged();


        if (!cb.onPreparePanel(st.featureId, st.createdPanelView, st.menu)) {
            if (mActionBar != null) {
                // The app didn't want to show the menu for now but it still exists.
                // Clear it out of the action bar.
                mActionBar.setMenu(null, mActionMenuPresenterCallback);
            }
            st.menu.startDispatchingItemsChanged();
            return false;
        }
        ... ...
    }

    // Set other state
    st.isPrepared = true;
    st.isHandled = false;
    mPreparedPanel = st;

    return true;
}

2. PhoneWindow.onKeyUp()

     跟KeyDown對應，按鍵起來之後會有一個up事件。而Menu的up事件也是又PhoneWindow來處理。

     1. onKeyUpPanel

protected boolean onKeyUp(int featureId, int keyCode, KeyEvent event) {
        ... ...
        case KeyEvent.KEYCODE_MENU: {
            onKeyUpPanel(featureId < 0 ? FEATURE_OPTIONS_PANEL : featureId,
                    event);
            return true;
        }
        ... ...
}

2.1 PhoneWindow.onKeyUpPanel(int featureId, KeyEvent event)

     1.  如果panel在前面的down事件中已經prepare成功了，調用  openPanel(st, event);去打開option menu。並且把    playSoundEffect 設爲 true;

          PS: 會打出Event log。

     2. 

public final void onKeyUpPanel(int featureId, KeyEvent event) {

    // The panel key was released, so clear the chording key
    if (mPanelChordingKey != 0) {
        ... ...
        boolean playSoundEffect = false;
        final PanelFeatureState st = getPanelState(featureId, true);
        if (featureId == FEATURE_OPTIONS_PANEL && mActionBar != null &&
                mActionBar.isOverflowReserved()) {
            if (mActionBar.getVisibility() == View.VISIBLE) {
                if (!mActionBar.isOverflowMenuShowing()) {
                    if (!isDestroyed() && preparePanel(st, event)) {
                        playSoundEffect = mActionBar.showOverflowMenu();
                    }
                } else {
                    playSoundEffect = mActionBar.hideOverflowMenu();
                }
            }
        } else {
            if (st.isOpen || st.isHandled) {

                // Play the sound effect if the user closed an open menu (and not if
                // they just released a menu shortcut)
                playSoundEffect = st.isOpen;

                // Close menu
                closePanel(st, true);

            } else if (st.isPrepared) {
                boolean show = true;
                if (st.refreshMenuContent) {
                    // Something may have invalidated the menu since we prepared it.
                    // Re-prepare it to refresh.
                    st.isPrepared = false;
                    show = preparePanel(st, event);
                }

                if (show) {
                    // Write 'menu opened' to event log
                    EventLog.writeEvent(50001, 0);

                    // Show menu
                    openPanel(st, event);

                    playSoundEffect = true;
                }
            }
        }

        if (playSoundEffect) {
            AudioManager audioManager = (AudioManager) getContext().getSystemService(
                    Context.AUDIO_SERVICE);
            if (audioManager != null) {
                audioManager.playSoundEffect(AudioManager.FX_KEY_CLICK);
            } else {
                Log.w(TAG, "Couldn't get audio manager");
            }
        }
    }
}

2.1.1 PhoneWindow.openPanel(PanelFeatureState st, KeyEvent event)

      在打開panel之前，會對平臺的屏幕進行檢測，如果發現不是手機，就直接返回。

      1. initializePanelDecor(PanelFeatureState st)  //初始化對應panel的DecorView； 如果menu沒有item的話，就直接return

      2. initializePanelContent(PanelFeatureState st)， //初始化Panel的MenuView，並賦給st.shownPanelView；

      3. 把st.shownPanelView寄到decorView中，然後通過wm.addView(st.decorView, lp);把新建出來的option menu的decorView加到WMS中。

     這樣option menu就顯示出來了。

private void openPanel(PanelFeatureState st, KeyEvent event) {

     Callback cb = getCallback();
     if ((cb != null) && (!cb.onMenuOpened(st.featureId, st.menu))) {
         // Callback doesn't want the menu to open, reset any state
         closePanel(st, true);
         return;
     }

     final WindowManager wm = getWindowManager();

     int width = WRAP_CONTENT;
     if (st.decorView == null || st.refreshDecorView) {
         if (st.decorView == null) {
             // Initialize the panel decor, this will populate st.decorView
             if (!initializePanelDecor(st) || (st.decorView == null))
                 return;
         } else if (st.refreshDecorView && (st.decorView.getChildCount() > 0)) {
             // Decor needs refreshing, so remove its views
             st.decorView.removeAllViews();
         }

         // This will populate st.shownPanelView
         if (!initializePanelContent(st) || !st.hasPanelItems()) {
             return;
         }

         ViewGroup.LayoutParams lp = st.shownPanelView.getLayoutParams();
         if (lp == null) {
             lp = new ViewGroup.LayoutParams(WRAP_CONTENT, WRAP_CONTENT);
         }

         int backgroundResId;
         if (lp.width == ViewGroup.LayoutParams.MATCH_PARENT) {
             // If the contents is fill parent for the width, set the
             // corresponding background
             backgroundResId = st.fullBackground;
             width = MATCH_PARENT;
         } else {
             // Otherwise, set the normal panel background
             backgroundResId = st.background;
         }
         st.decorView.setWindowBackground(getContext().getResources().getDrawable(
                 backgroundResId));

         ViewParent shownPanelParent = st.shownPanelView.getParent();
         if (shownPanelParent != null && shownPanelParent instanceof ViewGroup) {
             ((ViewGroup) shownPanelParent).removeView(st.shownPanelView);
         }
         st.decorView.addView(st.shownPanelView, lp);

         /*
          * Give focus to the view, if it or one of its children does not
          * already have it.
          */
         if (!st.shownPanelView.hasFocus()) {
             st.shownPanelView.requestFocus();
         }
     } else if (!st.isInListMode()) {
         width = MATCH_PARENT;
     } else if (st.createdPanelView != null) {
         // If we already had a panel view, carry width=MATCH_PARENT through
         // as we did above when it was created.
         ViewGroup.LayoutParams lp = st.createdPanelView.getLayoutParams();
         if (lp != null && lp.width == ViewGroup.LayoutParams.MATCH_PARENT) {
             width = MATCH_PARENT;
         }
     }

     st.isOpen = true;
     st.isHandled = false;

     WindowManager.LayoutParams lp = new WindowManager.LayoutParams(
             width, WRAP_CONTENT,
             st.x, st.y, WindowManager.LayoutParams.TYPE_APPLICATION_ATTACHED_DIALOG,
             WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM
             | WindowManager.LayoutParams.FLAG_SPLIT_TOUCH,
             st.decorView.mDefaultOpacity);

     if (st.isCompact) {
         lp.gravity = getOptionsPanelGravity();
         sRotationWatcher.addWindow(this);
     } else {
         lp.gravity = st.gravity;
     }

     lp.windowAnimations = st.windowAnimations;

     wm.addView(st.decorView, lp);
     // Log.v(TAG, "Adding main menu to window manager.");
 }

2.1.1.1     PhoneWindow.initializePanelDecor(PanelFeatureState st) 

        new出一個DecorView並且賦值給st.decorView。

protected boolean initializePanelDecor(PanelFeatureState st) {
    st.decorView = new DecorView(getContext(), st.featureId);
    st.gravity = Gravity.CENTER | Gravity.BOTTOM;
    st.setStyle(getContext());

    return true;
}

2.1.1.2 PhoneWindow. initializePanelContent(PanelFeatureState st) 

     //初始化Panel的MenuView，並賦給st.shownPanelView；

protected boolean initializePanelContent(PanelFeatureState st) {
    if (st.createdPanelView != null) {
        st.shownPanelView = st.createdPanelView;
        return true;
    }

    if (st.menu == null) {
        return false;
    }

    if (mPanelMenuPresenterCallback == null) {
        mPanelMenuPresenterCallback = new PanelMenuPresenterCallback();
    }

    MenuView menuView = st.isInListMode()
            ? st.getListMenuView(getContext(), mPanelMenuPresenterCallback)
            : st.getIconMenuView(getContext(), mPanelMenuPresenterCallback);

    st.shownPanelView = (View) menuView;

    if (st.shownPanelView != null) {
        // Use the menu View's default animations if it has any
        final int defaultAnimations = menuView.getWindowAnimations();
        if (defaultAnimations != 0) {
            st.windowAnimations = defaultAnimations;
        }
        return true;
    } else {
        return false;
    }
}