android - Snackbar getAnchorView() 与父视图

Question

我已阅读 Snackbar文档

但不确定小吃吧parentTarget（父视图）和anchoredView.

如果我错了，请纠正我：

1)parent view是小吃店从 hierchy 视图中向上走以找到suitable parent view.

2）合适的父视图不是anchoredView。

当一个人设置 a parentView（由ctor要求）并且还设置时会发生什么anchoredView？

小吃店在哪里开？

Answer 1

SnackBar的父视图将告诉应在哪个容器或布局上绘制快餐栏。通常，snackbar 从您作为参数传递的视图中寻找协调器布局作为父级，如果找不到它，它将把活动内容布局 (android.R.id.content) Framelayout 作为父级。

代码取自SnackBar

@Nullable
    private static ViewGroup findSuitableParent(View view) {
        ViewGroup fallback = null;
        do {
            if (view instanceof CoordinatorLayout) {
                // We've found a CoordinatorLayout, use it
                return (ViewGroup) view;
            } else if (view instanceof FrameLayout) {
                if (view.getId() == android.R.id.content) {
                    // If we've hit the decor content view, then we didn't find a CoL in the
                    // hierarchy, so use it.
                    return (ViewGroup) view;
                } else {
                    // It's not the content view but we'll use it as our fallback
                    fallback = (ViewGroup) view;
                }
            }
            if (view != null) {
                // Else, we will loop and crawl up the view hierarchy and try to find a parent
                final ViewParent parent = view.getParent();
                view = parent instanceof View ? (View) parent : null;
            }
        } while (view != null);
        // If we reach here then we didn't find a CoL or a suitable content view so we'll fallback
        return fallback;
    }

BaseTransientBottomBar的锚点会告诉您将在哪个视图上显示小吃吧。

代码取自BaseTransientBottomBar

private int calculateBottomMarginForAnchorView() {
    if (anchorView == null) {
      return 0;
    }

    int[] anchorViewLocation = new int[2];
    anchorView.getLocationOnScreen(anchorViewLocation);
    int anchorViewAbsoluteYTop = anchorViewLocation[1];

    int[] targetParentLocation = new int[2];
    targetParent.getLocationOnScreen(targetParentLocation);
    int targetParentAbsoluteYBottom = targetParentLocation[1] + targetParent.getHeight();

    return targetParentAbsoluteYBottom - anchorViewAbsoluteYTop;
  }

...

/** Sets the view the {@link BaseTransientBottomBar} should be anchored above. */
  @NonNull
  public B setAnchorView(@Nullable View anchorView) {
    this.anchorView = anchorView;
    return (B) this;
  }

  /**
   * Sets the id of the view the {@link BaseTransientBottomBar} should be anchored above.
   *
   * @throws IllegalArgumentException if the anchor view is not found.
   */
  @NonNull
  public B setAnchorView(@IdRes int anchorViewId) {
    this.anchorView = targetParent.findViewById(anchorViewId);
    if (this.anchorView == null) {
      throw new IllegalArgumentException("Unable to find anchor view with id: " + anchorViewId);
    }
    return (B) this;
  }

您可以在此处找到 SnackBar 的源代码Material SnackBar 和 BaseTransientBottomBar 在此处BaseTransientBottomBar