Android上下文菜單和上下文操作

定義上下文菜單資源

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android" >
    <item android:id="@+id/menu_item_delete_crime"
        android:icon="@android:drawable/ic_menu_delete"
        android:title="@string/delete_crime"/>

</menu>

實例化上下文菜單

@Override
    public void onCreateContextMenu(ContextMenu menu, View v,
            ContextMenuInfo menuInfo) {
        getActivity().getMenuInflater().inflate(R.menu.crime_list_item_context, menu);
    }

默認情況下，長按視圖不會觸發上下文菜單的創建。需要調用下面的函數使能上下文菜單功能：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    Log.d(TAG, "onCreateView");
    getActivity().setTitle(R.string.crime_title);
    View v = super.onCreateView(inflater, container, savedInstanceState);
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        if (mSubtitleVisible) {
            getActivity().getActionBar().setSubtitle(R.string.subtitle);
        }
    }
    // 爲上下文菜單登記視圖
    ListView listView = (ListView) v.findViewById(android.R.id.list);
    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
        // 低版本使用浮動操作
        registerForContextMenu(listView);
    } else {
        // 高版本使用操作欄模式，並開啓多選
        listView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE_MODAL);
        listView.setMultiChoiceModeListener(new MultiChoiceModeListener() {

            @Override
            public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
                return false;
            }

            @Override
            public void onDestroyActionMode(ActionMode mode) {
            }

            @Override
            public boolean onCreateActionMode(ActionMode mode, Menu menu) {
                MenuInflater inflater = mode.getMenuInflater();
                inflater.inflate(R.menu.crime_list_item_context, menu);
                return true;
            }

            @Override
            public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
                switch (item.getItemId()) {
                case R.id.menu_item_delete_crime:
                    CrimeAdapter adapter = (CrimeAdapter) getListAdapter();
                    CrimeLab crimeLab = CrimeLab.get(getActivity());
                    for (int i = adapter.getCount() - 1; i >= 0; i--) {
                        if (getListView().isItemChecked(i)) {
                            crimeLab.deleteCrime(adapter.getItem(i));
                        }
                    }
                    mode.finish();
                    adapter.notifyDataSetChanged();
                    return true;
                default:
                    return false;
                }
            }

            @Override
            public void onItemCheckedStateChanged(ActionMode mode, int position,
                    long id, boolean checked) {
            }
        });
    }
    return v;
}

改變背景

不向其它drawable資源,state list drawable資源通常和屏幕顯示像素密度無關，因而只存放在不帶修飾符的drawable目錄中。

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:drawable="@android:color/darker_gray" android:state_activated="true"></item>

</selector>

以上XML告訴我們：當引用該drawable資源的視圖處於激活狀態時，則使用android:drawable屬性指定的資源；反之，則不採取任何操作。

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