android Launcher onLongClick代码分析

       在launcher中，长按桌面会触发很多种行为。其分类包括：1、空白桌面；2、桌面内容（文件夹、快捷方式、文件夹等）；3、桌面既有控件（左右两个屏幕切换按钮，all app list按钮）等；因此我们很容易理解Launcher.java文件中onLongClick函数的行为：

 public boolean onLongClick(View v) {        switch (v.getId()) {            case R.id.previous_screen:                  if (!isAllAppsVisible()) {                    mWorkspace.performHapticFeedback(HapticFeedbackConstants.LONG_PRESS,                            HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING);                    showPreviews(v);                  }                return true;            case R.id.next_screen:                if (!isAllAppsVisible()) {                    mWorkspace.performHapticFeedback(HapticFeedbackConstants.LONG_PRESS,                            HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING);                    showPreviews(v);                }                return true;            case R.id.all_apps_button:                if (!isAllAppsVisible()) {                    mWorkspace.performHapticFeedback(HapticFeedbackConstants.LONG_PRESS,                            HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING);                    showPreviews(v);                }                return true;        }        //当不是跳转到别的屏幕，或者不是all_app_button被长按时，继续下面的处理。        if (isWorkspaceLocked()) {            return false;        }        if (!(v instanceof CellLayout)) {            v = (View) v.getParent();        }        CellLayout.CellInfo cellInfo = (CellLayout.CellInfo) v.getTag();        // This happens when long clicking an item with the dpad/trackball        if (cellInfo == null) {            return true;        }        if (mWorkspace.allowLongPress()) {            if (cellInfo.cell == null) {  //说明长按的地方是空白的                if (cellInfo.valid) {                     // User long pressed on empty space                    mWorkspace.setAllowLongPress(false);                    mWorkspace.performHapticFeedback(HapticFeedbackConstants.LONG_PRESS,                            HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING);                    showAddDialog(cellInfo); //长按的地方有效，则显示一个选择dialog                }            } else {//非空白                if (!(cellInfo.cell instanceof Folder)) {  //不是文件                    // User long pressed on an item                    mWorkspace.performHapticFeedback(HapticFeedbackConstants.LONG_PRESS,                            HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING);                    mWorkspace.startDrag(cellInfo);                }            }        }        return true;    }

        showAddDialog(cellInfo)继续调用showDialog(DIALOG_CREATE_SHORTCUT);此时可以搜索下，发现Launcher.java覆写了onCreateDialog方法：

@Override    protected Dialog onCreateDialog(int id) {        switch (id) {            case DIALOG_CREATE_SHORTCUT:                return new CreateShortcut().createDialog();            case DIALOG_RENAME_FOLDER:                return new RenameFolder().createDialog();        }        return super.onCreateDialog(id);    }

        可以看到，最终调用的是内部类CreateShortcut的createDialog()方法来创建一个选择Dialog。

        继续分析createDialog()方法，可以看到它初始化了一个AddAdapter：

mAdapter = new AddAdapter(Launcher.this);

        跟进去发现，这就是Dialog上显示的菜单的初始化位置：

 public AddAdapter(Launcher launcher) {        super();        mInflater = (LayoutInflater) launcher.getSystemService(Context.LAYOUT_INFLATER_SERVICE);        // Create default actions        Resources res = launcher.getResources();                mItems.add(new ListItem(res, R.string.group_shortcuts,                R.drawable.ic_launcher_shortcut, ITEM_SHORTCUT));  //shortcut        mItems.add(new ListItem(res, R.string.group_widgets,                R.drawable.ic_launcher_appwidget, ITEM_APPWIDGET));//widget                mItems.add(new ListItem(res, R.string.group_live_folders,                R.drawable.ic_launcher_folder, ITEM_LIVE_FOLDER));//folder                mItems.add(new ListItem(res, R.string.group_wallpapers,                R.drawable.ic_launcher_wallpaper, ITEM_WALLPAPER));//wallpaper    }

        这样，选择Dialog就出现了，下面是它的响应函数，同理，在CreateShortcut内部类中实现了onClick()函数：

 public void onClick(DialogInterface dialog, int which) {            Resources res = getResources();            cleanup();            //CR 249200 Modify start            isClicked = true;            //CR 249200 Modify end            switch (which) {                case AddAdapter.ITEM_SHORTCUT: {  //shortcut处理                    // Insert extra item to handle picking application                    pickShortcut();                    break;                }                case AddAdapter.ITEM_APPWIDGET: {  //widget处理                    int appWidgetId = Launcher.this.mAppWidgetHost.allocateAppWidgetId();                    Intent pickIntent = new Intent(AppWidgetManager.ACTION_APPWIDGET_PICK);                    pickIntent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetId);                    // start the pick activity                    startActivityForResult(pickIntent, REQUEST_PICK_APPWIDGET);                    break;                }                case AddAdapter.ITEM_LIVE_FOLDER: {  //文件夹处理                    // Insert extra item to handle inserting folder                    Bundle bundle = new Bundle();                    ArrayList<String> shortcutNames = new ArrayList<String>();                    shortcutNames.add(res.getString(R.string.group_folder));                    bundle.putStringArrayList(Intent.EXTRA_SHORTCUT_NAME, shortcutNames);                    ArrayList<ShortcutIconResource> shortcutIcons =                            new ArrayList<ShortcutIconResource>();                    shortcutIcons.add(ShortcutIconResource.fromContext(Launcher.this,                            R.drawable.ic_launcher_folder));                    bundle.putParcelableArrayList(Intent.EXTRA_SHORTCUT_ICON_RESOURCE, shortcutIcons);                    Intent pickIntent = new Intent(Intent.ACTION_PICK_ACTIVITY);                    pickIntent.putExtra(Intent.EXTRA_INTENT,                            new Intent(LiveFolders.ACTION_CREATE_LIVE_FOLDER));                    pickIntent.putExtra(Intent.EXTRA_TITLE,                            getText(R.string.title_select_live_folder));                    pickIntent.putExtras(bundle);                    startActivityForResult(pickIntent, REQUEST_PICK_LIVE_FOLDER);                    break;                }                case AddAdapter.ITEM_WALLPAPER: {  //选择壁纸                    startWallpaper();                    break;                }            }        }

        如上，长按的动作就分析完了，当onClick()函数接收到不同的动作后，会分派到不同的函数去处理。