PopupMenu使用步骤
//这里的anchor是PopupMenu需要依附的view
PopupMenu popupMenu = new PopupMenu(context, anchor);
//填充PopupMenu内容
popupMenu.getMenuInflater().inflate(R.menu.conversation_item_popupmenu, popupMenu.getMenu());
//PopupMenu点击事件
popupMenu.setOnMenuItemClickListener(onMenuItemClickListener);
//PopupMenu消失事件
popupMenu.setOnDismissListener(onDismissListener);
//弹出PopupMenu，默认gravity为Gravity.START
popupMenu.show();
弹出效果如下图所示
Gravity.START
可以使用setGravity()方法来指定弹出窗口与anchor视图的对齐方式，例如修改对齐方式为Gravity.END
Gravity.END
使用起来还是比较简单的，但是好像大部分项目的需求是PopupMenu在用户点击的位置弹出，然而PopupMenu并没有提供在指定坐标弹出的方法，所以只能咱们自己来实现咯！
想让PopupMenu在指定弹出位置，首先咱们得先了解show()方法是如何让PopupMenu弹出来的，所以只能去阅读源码了（Read The Fucking Source Code~）。
public void show() {
mPopup.show();
}
PopupMenu的show()方法很简单，直接把任务转给MenuPopupHelper来处理，处理流程：show() -> tryShow() -> showPopup(0, 0, false, false);
public void show() {
if (!tryShow()) {
throw new IllegalStateException("MenuPopupHelper cannot be used without an anchor");
}
}
//安全判断，检测是否有anchor view
public boolean tryShow() {
if (isShowing()) {
return true;
}
if (mAnchorView == null) {
return false;
}
//这就是我们要找的方法，默认坐标是（0,0）
showPopup(0, 0, false, false);
return true;
}
//xOffset 相对于anchor视图的x坐标
//yOffset 相对于anchor视图的y坐标
private void showPopup(int xOffset, int yOffset, boolean useOffsets, boolean showTitle) {
final MenuPopup popup = getPopup();
popup.setShowTitle(showTitle);
if (useOffsets) {
// If the resolved drop-down gravity is RIGHT, the popup's right
// edge will be aligned with the anchor view. Adjust by the anchor
// width such that the top-right corner is at the X offset.
final int hgrav = GravityCompat.getAbsoluteGravity(mDropDownGravity,
ViewCompat.getLayoutDirection(mAnchorView)) & Gravity.HORIZONTAL_GRAVITY_MASK;
if (hgrav == Gravity.RIGHT) {
xOffset -= mAnchorView.getWidth();
}
popup.setHorizontalOffset(xOffset);
popup.setVerticalOffset(yOffset);
// Set the transition epicenter to be roughly finger (or mouse
// cursor) sized and centered around the offset position. This
// will give the appearance that the window is emerging from
// the touch point.
final float density = mContext.getResources().getDisplayMetrics().density;
final int halfSize = (int) (TOUCH_EPICENTER_SIZE_DP * density / 2);
final Rect epicenter = new Rect(xOffset - halfSize, yOffset - halfSize,
xOffset + halfSize, yOffset + halfSize);
popup.setEpicenterBounds(epicenter);
}
popup.show();
}
我们可以看到showPopup方法内有两个参数int xOffset、int yOffset，根据注释可以知道这就是相对于anchor视图的坐标值。所以如果要指定PopupMenu的弹出位置，MenuPopupHelper应该这样处理弹出逻辑：show(int x, int y) -> tryShow(int x, int y) -> showPopup(x, y, true, true)。
但是由于PopupMenu无法调用到MenuPopupHelper的show(int x, int y) 方法，因此我们只能使用反射机制绕过PopupMenu，直接调用MenuPopupHelper的show(int x, int y)方法。
到此为止，已经有了大致的解决思路，接下来看看具体实现。
/**
* 弹出菜单栏
*
* @param context
* @param anchor 触发事件的View
* @param menuRes 菜单栏内容
* @param point 点击事件相对整个屏幕的坐标
* @param onMenuItemClickListener 菜单栏点击事件
* @param onDismissListener 菜单栏消失
*/
public static void showPopupMenu(Context context, View anchor, @MenuRes int menuRes, Point point,
PopupMenu.OnMenuItemClickListener onMenuItemClickListener,
PopupMenu.OnDismissListener onDismissListener) {
//这里的anchor代表PopupMenu需要依附的view
PopupMenu popupMenu = new PopupMenu(context, anchor);
//填充PopupMenu内容
popupMenu.getMenuInflater().inflate(menuRes, popupMenu.getMenu());
//PopupMenu点击事件
popupMenu.setOnMenuItemClickListener(onMenuItemClickListener);
//PopupMenu消失事件
popupMenu.setOnDismissListener(onDismissListener);
//通过反射机制修改弹出位置，在点击的位置弹出PopupMenu
try {
//获取PopupMenu类的成员变量MenuPopupHelper mPopup
Field mPopup = popupMenu.getClass().getDeclaredField("mPopup");
mPopup.setAccessible(true);
Object o = mPopup.get(popupMenu);
//MenuPopupHelper -> show(int x, int y)方法
if (o instanceof MenuPopupHelper) {
MenuPopupHelper menuPopupHelper = (MenuPopupHelper) o;
int[] position = new int[2];
//获取anchor左上角在屏幕上的相对坐标
anchor.getLocationInWindow(position);
//计算xOffset、yOffset，相对anchor左下角位置为弹出位置
int xOffset = (point.x - position[0]);
int yOffset;
//菜单高度
int popupMenuHeight = DensityUtil.dp2px(context, 48 * popupMenu.getMenu().size());
//如果菜单高度大于底部剩余空间，菜单就会向上弹出；否则向下弹出
if (ScreenUtil.getScreenHeight(context) - point.y >= popupMenuHeight) {
yOffset = (point.y - (position[1] + anchor.getHeight()));
} else {
yOffset = (point.y - (position[1]));
}
menuPopupHelper.show(xOffset, yOffset);
}
} catch (NoSuchFieldException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} finally {
//出错时调用普通show方法。未出错时此方法也不会影响正常显示
popupMenu.show();
}
}
最终弹出效果如下图所示
指定位置弹出
