ListView的长按菜单

Android的listview可以长按弹出来一个菜单。

 

今天就跟了下代码大概看了下弹出菜单的流程。

 

我们实现一个菜单长按步骤通常如下：

1、弹出菜单的生成

如果控制listview长按应该生成什么样的菜单。

a、生成一个OnCreateContextMenuListener的接口对象l

该接口定义如下：在view.java中

public interface OnCreateContextMenuListener { /** * Called when the context menu for this view is being built. It is not * safe to hold onto the menu after this method returns. * * @param menu The context menu that is being built * @param v The view for which the context menu is being built * @param menuInfo Extra information about the item for which the * context menu should be shown. This information will vary * depending on the class of v. */ void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo); }

b、实现该接口的onCreateContextMenu(ContextMenu menu, View v,
                ContextMenuInfo menuInfo)函数

在这里，根据menuInfo，通常先转换为AdapterContextMenuInfo，定义如下，在adapterview.java中定义

public static class AdapterContextMenuInfo implements ContextMenu.ContextMenuInfo { public AdapterContextMenuInfo(View targetView, int position, long id) { this.targetView = targetView; this.position = position; this.id = id; } /** * The child view for which the context menu is being displayed. This * will be one of the children of this AdapterView. */ public View targetView; /** * The position in the adapter for which the context menu is being * displayed. */ public int position; /** * The row id of the item for which the context menu is being displayed. */ public long id; }

通过获取MenuItem 的postion进而获取该listitem的信息，进而来决定加入什么样的菜单。

 

c、将该接口对象设置为listview的listener

setOnCreateContextMenuListener(l)

2、菜单选择事件的响应

实现该listview的单击响应事件

public boolean onContextItemSelected(MenuItem item) {}

根据不同的MenuItem的id来进行不同的操作。

 

 

 

二、onCreateContextMenu的调用

那么OnCreateContextMenuListener的onCreateContextMenu是在什么时候调用的呢

是在view.java中createContextMenu函数中调用。

view.createContextMenu是在ContextMenubuilder的show函数调用

而ContextMenubuilder的show函数分别在

PhoneWindow和MidWindow的showContextMenuForChild调用。

再往下今天就没再跟下去了。

 

三、onCreateContextMenu的生成

在onCreateContextMenu(menu, this, menuInfo)时，传入一个MenuInfo，我们就根据这个MenuInfo来创建响应的菜单。

那这个MenuInfo是怎样生成的呢？

1、首先在View中createContextMenu，调用ContextMenuInfo menuInfo = getContextMenuInfo();

但是getContextMenuInfo()就是返回一个空，得不得我们的数据。

所以，一个view要想能够生成自己的MenuInfo，必须要重新getContextMenuInfo这个函数。

2、在上面的步骤中，我们没有涉及到该函数的重写 ，是因为ListView的父类中，已经重写了改函数 。如下

@Override protected ContextMenuInfo getContextMenuInfo() { return mContextMenuInfo; }

而这个成员变量的赋值如下：

 

private boolean performLongPress(final View child, final int longPressPosition, final long longPressId) { boolean handled = false; if (mOnItemLongClickListener != null) { handled = mOnItemLongClickListener.onItemLongClick(AbsListView.this, child, longPressPosition, longPressId); } if (!handled) { mContextMenuInfo = createContextMenuInfo(child, longPressPosition, longPressId); handled = super.showContextMenuForChild(AbsListView.this); } if (handled) { performHapticFeedback(HapticFeedbackConstants.LONG_PRESS); } return handled; } ContextMenuInfo createContextMenuInfo(View view, int position, long id) { return new AdapterContextMenuInfo(view, position, id); } ContextMenuInfo createContextMenuInfo(View view, int position, long id) { return new AdapterContextMenuInfo(view, position, id); }

 

就是我们在构造菜单时候所用到的ContextMenuInfo.

 

如果我们要给其它自己定义的View，响应长按菜单。这时候我们就需要重写该View的getContextMenuInfo()。

根据View当前状态生成不同的ContextMenuInfo,进而决定应该弹出什么样的菜单。