public void showAsDropDown(View anchor, int xoff, int yoff, int gravity) {    if (isShowing() || mContentView == null) {      return;    }    registerForScrollChanged(anchor, xoff, yoff, gravity);    mIsShowing = true;    mIsDropdown = true;    WindowManager.LayoutParams p = createPopupLayout(anchor.getWindowToken());    preparePopup(p);    updateAboveAnchor(findDropDownPosition(anchor, p, xoff, yoff, gravity));    if (mHeightMode < 0) p.height = mLastHeight = mHeightMode;    if (mWidthMode < 0) p.width = mLastWidth = mWidthMode;    p.windowAnimations = computeAnimationResource();    invokePopup(p); }

  /**   * <p>Prepare the popup by embedding in into a new ViewGroup if the   * background drawable is not null. If embedding is required, the layout   * parameters' height is modified to take into account the background's   * padding.</p>   *   * @param p the layout parameters of the popup's content view   */  private void preparePopup(WindowManager.LayoutParams p) {    if (mContentView == null || mContext == null || mWindowManager == null) {      throw new IllegalStateException("You must specify a valid content view by "          + "calling setContentView() before attempting to show the popup.");    }    if (mBackground != null) {      final ViewGroup.LayoutParams layoutParams = mContentView.getLayoutParams();      int height = ViewGroup.LayoutParams.MATCH_PARENT;      if (layoutParams != null &&          layoutParams.height == ViewGroup.LayoutParams.WRAP_CONTENT) {        height = ViewGroup.LayoutParams.WRAP_CONTENT;      }      // when a background is available, we embed the content view      // within another view that owns the background drawable      PopupViewContainer popupViewContainer = new PopupViewContainer(mContext);      PopupViewContainer.LayoutParams listParams = new PopupViewContainer.LayoutParams(          ViewGroup.LayoutParams.MATCH_PARENT, height      );      popupViewContainer.setBackground(mBackground);      popupViewContainer.addView(mContentView, listParams);      mPopupView = popupViewContainer;    } else {      mPopupView = mContentView;    }    mPopupView.setElevation(mElevation);    mPopupViewInitialLayoutDirectionInherited =        (mPopupView.getRawLayoutDirection() == View.LAYOUT_DIRECTION_INHERIT);    mPopupWidth = p.width;    mPopupHeight = p.height;  }

  private class PopupViewContainer extends FrameLayout {    private static final String TAG = "PopupWindow.PopupViewContainer";    public PopupViewContainer(Context context) {      super(context);    }    @Override    protected int[] onCreateDrawableState(int extraSpace) {      if (mAboveAnchor) {        // 1 more needed for the above anchor state        final int[] drawableState = super.onCreateDrawableState(extraSpace + 1);        View.mergeDrawableStates(drawableState, ABOVE_ANCHOR_STATE_SET);        return drawableState;      } else {        return super.onCreateDrawableState(extraSpace);      }    }    @Override    public boolean dispatchKeyEvent(KeyEvent event) {　　// 這個(gè)方法里面實(shí)現(xiàn)了返回鍵處理邏輯，會(huì)調(diào)用dismiss      if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {        if (getKeyDispatcherState() == null) {          return super.dispatchKeyEvent(event);        }        if (event.getAction() == KeyEvent.ACTION_DOWN            && event.getRepeatCount() == 0) {          KeyEvent.DispatcherState state = getKeyDispatcherState();          if (state != null) {            state.startTracking(event, this);          }          return true;        } else if (event.getAction() == KeyEvent.ACTION_UP) {          KeyEvent.DispatcherState state = getKeyDispatcherState();          if (state != null && state.isTracking(event) && !event.isCanceled()) {            dismiss();            return true;          }        }        return super.dispatchKeyEvent(event);      } else {        return super.dispatchKeyEvent(event);      }    }    @Override    public boolean dispatchTouchEvent(MotionEvent ev) {      if (mTouchInterceptor != null && mTouchInterceptor.onTouch(this, ev)) {        return true;      }      return super.dispatchTouchEvent(ev);    }    @Override    public boolean onTouchEvent(MotionEvent event) { // 這個(gè)方法里面實(shí)現(xiàn)點(diǎn)擊消失邏輯      final int x = (int) event.getX();      final int y = (int) event.getY();            if ((event.getAction() == MotionEvent.ACTION_DOWN)          && ((x < 0) || (x >= getWidth()) || (y < 0) || (y >= getHeight()))) {        dismiss();        return true;      } else if (event.getAction() == MotionEvent.ACTION_OUTSIDE) {        dismiss();        return true;      } else {        return super.onTouchEvent(event);      }    }    @Override    public void sendAccessibilityEvent(int eventType) {      // clinets are interested in the content not the container, make it event source      if (mContentView != null) {        mContentView.sendAccessibilityEvent(eventType);      } else {        super.sendAccessibilityEvent(eventType);      }    }  }

  /**   * Specifies the background drawable for this popup window. The background   * can be set to {@code null}.   *   * @param background the popup's background   * @see #getBackground()   * @attr ref android.R.styleable#PopupWindow_popupBackground   */  public void setBackgroundDrawable(Drawable background) {    mBackground = background;    // 省略其他的  }

  /**   * <p>Create a new, empty, non focusable popup window of dimension (0,0).</p>   *    * <p>The popup does not provide a background.</p>   */  public PopupWindow(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {    mContext = context;    mWindowManager = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);    final TypedArray a = context.obtainStyledAttributes(        attrs, R.styleable.PopupWindow, defStyleAttr, defStyleRes);    final Drawable bg = a.getDrawable(R.styleable.PopupWindow_popupBackground);    mElevation = a.getDimension(R.styleable.PopupWindow_popupElevation, 0);    mOverlapAnchor = a.getBoolean(R.styleable.PopupWindow_overlapAnchor, false);    final int animStyle = a.getResourceId(R.styleable.PopupWindow_popupAnimationStyle, -1);    mAnimationStyle = animStyle == R.style.Animation_PopupWindow ? -1 : animStyle;    a.recycle();    setBackgroundDrawable(bg);  }

  /**   * Prepare the popup by embedding it into a new ViewGroup if the background   * drawable is not null. If embedding is required, the layout parameters'   * height is modified to take into account the background's padding.   *   * @param p the layout parameters of the popup's content view   */  private void preparePopup(WindowManager.LayoutParams p) {    if (mContentView == null || mContext == null || mWindowManager == null) {      throw new IllegalStateException("You must specify a valid content view by "          + "calling setContentView() before attempting to show the popup.");    }    // The old decor view may be transitioning out. Make sure it finishes    // and cleans up before we try to create another one.    if (mDecorView != null) {      mDecorView.cancelTransitions();    }    // When a background is available, we embed the content view within    // another view that owns the background drawable.    if (mBackground != null) {      mBackgroundView = createBackgroundView(mContentView);      mBackgroundView.setBackground(mBackground);    } else {      mBackgroundView = mContentView;    }    mDecorView = createDecorView(mBackgroundView);    // The background owner should be elevated so that it casts a shadow.    mBackgroundView.setElevation(mElevation);    // We may wrap that in another view, so we'll need to manually specify    // the surface insets.    final int surfaceInset = (int) Math.ceil(mBackgroundView.getZ() * 2);    p.surfaceInsets.set(surfaceInset, surfaceInset, surfaceInset, surfaceInset);    p.hasManualSurfaceInsets = true;    mPopupViewInitialLayoutDirectionInherited =        (mContentView.getRawLayoutDirection() == View.LAYOUT_DIRECTION_INHERIT);    mPopupWidth = p.width;    mPopupHeight = p.height;  }