[转]于Fragment和Activity之间onCreateOptionsMenu的问题

Fragment和Activity一样，可以重写onCreateOptionsMenu方法来设定自己的菜单，其实这两个地方使用onCreateOptionsMenu的目的和效果都是完全一样的，但是由于Fragment是从属于activity的，因此第一次使用onCreateOptionsMenu的时候需要注意以下知识点。

一、在Activity和Fragment中onCreateOptionsMenu的实现是有细微差别的：

在activity中：

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@Override public boolean onCreateOptionsMenu(Menu menu) {     getMenuInflater().inflate(R.menu.main, menu);     return super.onCreateOptionsMenu(menu); }

在Fragment中：

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@Override public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {         inflater.inflate(R.menu.pictrue_list, menu);         super.onCreateOptionsMenu(menu,inflater); }

两者不同的地方在于

（1）一个有返回值（boolean类型），一个没有返回值。

（2）Fragment中onCreateOptionsMenu的参数多了一个MenuInflater

 

二、想让Fragment中的onCreateOptionsMenu生效必须先调用setHasOptionsMenu方法

一般我们是在nCreate中调用

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@Override public void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     mBucketId = getArguments().getInt(Images.Media.BUCKET_ID);     mCallback = new ModeCallback();     setHasOptionsMenu(true); }

三、如果Fragment和Activity都同时inflate了一个menu资源文件，那么menu资源所包含的菜单会出现两次

为什么呢，因为inflater.inflate(R.menu.pictrue_list, menu)方法的作用其实就是将第一个参数中包括的菜单项追加到menu中。一开始，在activity中menu是空的，当调用了getMenuInflater().inflate(R.menu.main, menu)

menu中便有了菜单项，而在执行到Fragment的(Menu menu, MenuInflater inflater)时，activity的menu就传递下来，作为第一个参数。activity和Fragment中的menu其实是一个对象。

我还可以从上面的分析中得出，Fragment的菜单项会显示在Activity菜单项的后面。

 

为了解决menu资源所包含的菜单会出现两次这个问题，一般我们让Activity和Fragment  inflate两个不同的菜单（就如上面的例子），Fragment会继承Activity的所有菜单。

 

四、如果在Fragment和Activity中有相同的菜单元素，并且activity和fragment都对此菜单有响应的话，那么将执行两次响应事件。

除此之外，该菜单元素会显示两次。


举例说明：

activity中的菜单资源：

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<menu xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:app="http://schemas.android.com/apk/res-auto"     xmlns:tools="http://schemas.android.com/tools"     tools:context="com.example.acctionbaractivitydemo.MainActivity" >     <item         android:id="@+id/take_pic"         android:title=""         android:icon="@drawable/ic_action_camera"         app:showAsAction="withText|ifRoom"/>     <item         android:id="@+id/multi_select"         android:title="@string/multi_select"         app:showAsAction="withText|ifRoom"/>     <item         android:id="@+id/theme_color_pick"         android:orderInCategory="100"         android:title="@string/theme_color_pick"         app:showAsAction="never"/>              </menu>

fragment中：

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<menu xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:app="http://schemas.android.com/apk/res-auto"     xmlns:tools="http://schemas.android.com/tools"     tools:context="com.example.acctionbaractivitydemo.MainActivity" >     <item         android:id="@+id/multi_select"         android:title="@string/multi_select"         app:showAsAction="withText|ifRoom"/>                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          <item         android:id="@+id/show_in_detail"         android:orderInCategory="100"         android:title="@string/show_in_detail"         app:showAsAction="never"/>                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    </menu>

他们有相同的菜单multi_select（主要是id相同）。

这时如果activity中

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@Override public boolean onOptionsItemSelected(MenuItem item) {     switch(item.getItemId()){               case  R.id.take_pic:             capturePicture();             break;                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 case  R.id.multi_select:             Toast.makeText(MainActivity.this, "ss", 500).show();             break;          }     return super.onOptionsItemSelected(item); }

Fragment中：

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@Override public boolean onOptionsItemSelected(MenuItem item) {     switch(item.getItemId()){       case  R.id.multi_select:         mGridView.setItemChecked(0,true);         mGridView.clearChoices();         mCallback.updateSeletedCount();         break;                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       case  R.id.show_in_detail:         break;              }     return super.onOptionsItemSelected(item); }

那么两者的case R.id.multi_select代码块都会执行。