Smart / Simple / Savory life of Jason Yeh: 2015

常常在設計Android程式的時候，需要從系統撈一些參數與資訊，但是卻必須要提供其在Android resource xml檔案中的名稱與索引，寫一個範例如下方便使用。

int size;
size = GetResourceSize("status_bar_height");

private int GetResourceSize(String resource_name)
{
 int resourceId = getResources().getIdentifier(resource_name, "dimen", "android");
 if(resourceId >0)
  return getResources().getDimensionPixelSize(resourceId);
 return 0;
}

相關的資源檔範例：

<?xml version="1.0" encoding="utf-8"?>
<!--
/* //device/apps/common/assets/res/any/dimens.xml
**
** Copyright 2006, The Android Open Source Project
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
**     http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/
-->
<resources>
    <!-- The width that is used when creating thumbnails of applications. -->
    <dimen name="thumbnail_width">164dp</dimen>
    <!-- The height that is used when creating thumbnails of applications. -->
    <dimen name="thumbnail_height">145dp</dimen>
    <!-- The standard size (both width and height) of an application icon that
         will be displayed in the app launcher and elsewhere. -->
    <dimen name="app_icon_size">48dip</dimen>
    <!-- The maximum number of action buttons that should be permitted within
         an action bar/action mode. This will be used to determine how many
         showAsAction="ifRoom" items can fit. "always" items can override this. -->
    <integer name="max_action_buttons">2</integer>
    <dimen name="toast_y_offset">64dip</dimen>
    <!-- Height of the status bar -->
    <dimen name="status_bar_height">25dip</dimen>
    <!-- Height of the bottom navigation / system bar. -->
    <dimen name="navigation_bar_height">48dp</dimen>
    <!-- Height of the bottom navigation bar in portrait; often the same as @dimen/navigation_bar_height -->
    <dimen name="navigation_bar_height_landscape">48dp</dimen>
    <!-- Width of the navigation bar when it is placed vertically on the screen -->
    <dimen name="navigation_bar_width">42dp</dimen>
    <!-- Height of notification icons in the status bar -->
    <dimen name="status_bar_icon_size">24dip</dimen>
    <!-- Size of the giant number (unread count) in the notifications -->
    <dimen name="status_bar_content_number_size">48sp</dimen>
    <!-- Height of the system bar (combined status & navigation); used by
         SystemUI internally, not respected by the window manager. -->
    <dimen name="system_bar_height">@dimen/navigation_bar_height</dimen>
    <!-- Height of notification icons in the system bar -->
    <dimen name="system_bar_icon_size">32dip</dimen>
    <!-- Margin at the edge of the screen to ignore touch events for in the windowshade. -->
    <dimen name="status_bar_edge_ignore">5dp</dimen>
    <!-- Size of the fastscroll hint letter -->
    <dimen name="fastscroll_overlay_size">104dp</dimen>
    <!-- Width of the fastscroll thumb -->
    <dimen name="fastscroll_thumb_width">64dp</dimen>
    <!-- Height of the fastscroll thumb -->
    <dimen name="fastscroll_thumb_height">52dp</dimen>
    <!-- Min width for a tablet device -->
    <dimen name="min_xlarge_screen_width">800dp</dimen>
    <!-- Default height of a key in the password keyboard for alpha (used by keyguard) -->
    <dimen name="password_keyboard_key_height_alpha">56dip</dimen>
    <!-- Default height of a key in the password keyboard for numeric (used by keyguard) -->
    <dimen name="password_keyboard_key_height_numeric">56dip</dimen>
    <!-- Default correction for the space key in the password keyboard  (used by keyguard) -->
    <dimen name="password_keyboard_spacebar_vertical_correction">4dip</dimen>
    <!-- Default horizontal gap between keys in the password keyboard (used by keyguard) -->
    <dimen name="password_keyboard_horizontalGap">3dip</dimen>
    <!-- Default vertical gap between keys in the password keyboard (used by keyguard) -->
    <dimen name="password_keyboard_verticalGap">9dip</dimen>
    <!-- Size of lockscreen outerring on unsecure unlock LockScreen -->
    <dimen name="keyguard_lockscreen_outerring_diameter">270dp</dimen>
    <!-- Default target placement radius for MultiWaveView -->
    <dimen name="multiwaveview_target_placement_radius">135dip</dimen>
    <!-- Default distance beyond which MultiWaveView snaps to the target radius -->
    <dimen name="multiwaveview_snap_margin">20dip</dimen>
    <!-- Default distance from each snap target that MultiWaveView considers a "hit" -->
    <dimen name="multiwaveview_hit_radius">60dip</dimen>
    <!-- Preference activity side margins -->
    <dimen name="preference_screen_side_margin">0dp</dimen>
    <!-- Preference activity side margins negative-->
    <dimen name="preference_screen_side_margin_negative">0dp</dimen>
    <!-- Preference activity top margin -->
    <dimen name="preference_screen_top_margin">0dp</dimen>
    <!-- Preference activity bottom margin -->
    <dimen name="preference_screen_bottom_margin">0dp</dimen>
    <!-- Preference widget area width (to the left of the text) -->
    <dimen name="preference_widget_width">48dp</dimen>
    <!-- Preference fragment padding, bottom -->
    <dimen name="preference_fragment_padding_bottom">0dp</dimen>
    <!-- Preference fragment padding, sides -->
    <dimen name="preference_fragment_padding_side">16dp</dimen>
    <!-- Weight of the left pane in a multi-pane preference layout. -->
    <integer name="preferences_left_pane_weight">4</integer>
    <!-- Weight of the right pane in a multi-pane preference layout. So the split is 40:60 -->
    <integer name="preferences_right_pane_weight">6</integer>
    <!-- Padding to the left of the preference panel breadcrumb -->
    <dimen name="preference_breadcrumb_paddingLeft">0dp</dimen>
    <!-- Padding to the right of the preference panel breadcrumb -->
    <dimen name="preference_breadcrumb_paddingRight">0dp</dimen>
    <!-- Minimum space to allocate to the left of a preference item for an icon.
        This helps in aligning titles when some items have icons and some don't. When space is
        at a premium, we don't pre-allocate any space. -->
    <dimen name="preference_icon_minWidth">0dp</dimen>
    <!-- The platform's desired minimum size for a dialog's width when it
         is along the major axis (that is the screen is landscape).  This may
         be either a fraction or a dimension. -->
    <item type="dimen" name="dialog_min_width_major">65%</item>
    <!-- The platform's desired fixed width for a dialog along the major axis
         (the screen is in landscape). This may be either a fraction or a dimension.-->
    <item type="dimen" name="dialog_fixed_width_major">320dp</item>
    <!-- The platform's desired fixed width for a dialog along the minor axis
         (the screen is in portrait). This may be either a fraction or a dimension.-->
    <item type="dimen" name="dialog_fixed_width_minor">320dp</item>
    <!-- The platform's desired fixed height for a dialog along the major axis
         (the screen is in portrait). This may be either a fraction or a dimension.-->
    <item type="dimen" name="dialog_fixed_height_major">80%</item>
    <!-- The platform's desired fixed height for a dialog along the minor axis
         (the screen is in landscape). This may be either a fraction or a dimension.-->
    <item type="dimen" name="dialog_fixed_height_minor">100%</item>
    <!-- Preference activity, vertical padding for the header list -->
    <dimen name="preference_screen_header_vertical_padding">0dp</dimen>
    <dimen name="preference_screen_header_padding_side">16dip</dimen>
    <integer name="preference_screen_header_scrollbarStyle">0x02000000</integer> <!-- outsideOverlay -->
    <integer name="preference_fragment_scrollbarStyle">0x02000000</integer> <!-- outsideOverlay -->
    <dimen name="preference_item_padding_side">8dip</dimen>
    <dimen name="preference_item_padding_inner">8dip</dimen>
    <dimen name="preference_child_padding_side">16dip</dimen>
    <!-- The platform's desired minimum size for a dialog's width when it
         is along the minor axis (that is the screen is portrait).  This may
         be either a fraction or a dimension. -->
    <item type="dimen" name="dialog_min_width_minor">95%</item>
    <!-- The width of the big icons in notifications. -->
    <dimen name="notification_large_icon_width">64dp</dimen>
    <!-- The width of the big icons in notifications. -->
    <dimen name="notification_large_icon_height">64dp</dimen>
    <!-- Minimum width of the search view text entry area. -->
    <dimen name="search_view_text_min_width">160dip</dimen>
    <!-- Preferred width of the search view. -->
    <dimen name="search_view_preferred_width">320dip</dimen>
    <!-- Dialog title height -->
    <dimen name="alert_dialog_title_height">64dip</dimen>
    <!-- Dialog button bar height -->
    <dimen name="alert_dialog_button_bar_height">48dip</dimen>
    <!-- Default height of an action bar. -->
    <dimen name="action_bar_default_height">48dip</dimen>
    <!-- Vertical padding around action bar icons. -->
    <dimen name="action_bar_icon_vertical_padding">8dip</dimen>
    <!-- Text size for action bar titles -->
    <dimen name="action_bar_title_text_size">18dp</dimen>
    <!-- Text size for action bar subtitles -->
    <dimen name="action_bar_subtitle_text_size">14dp</dimen>
    <!-- Top margin for action bar subtitles -->
    <dimen name="action_bar_subtitle_top_margin">-3dp</dimen>
    <!-- Bottom margin for action bar subtitles -->
    <dimen name="action_bar_subtitle_bottom_margin">5dip</dimen>
    <!-- Size of clock font in LockScreen on Unsecure unlock screen. -->
    <dimen name="keyguard_lockscreen_clock_font_size">80dip</dimen>
    <!-- Size of status line font on Unsecure unlock LockScreen. -->
    <dimen name="keyguard_lockscreen_status_line_font_size">14dip</dimen>
    <!-- Size of right margin on Unsecure unlock LockScreen -->
    <dimen name="keyguard_lockscreen_status_line_font_right_margin">42dip</dimen>
    <!-- Size of top margin on Clock font to edge on unlock LockScreen -->
    <dimen name="keyguard_lockscreen_status_line_clockfont_top_margin">22dip</dimen>
    <!-- Size of top margin on Clock font to edge on unlock LockScreen -->
    <dimen name="keyguard_lockscreen_status_line_clockfont_bottom_margin">12dip</dimen>
    <!-- Padding on left margin of PIN text entry field to center it when del button is showing -->
    <dimen name="keyguard_lockscreen_pin_margin_left">40dip</dimen>
    <!-- Minimum popup width for selecting an activity in ActivityChooserDialog/ActivityChooserView. -->
    <dimen name="activity_chooser_popup_min_width">200dip</dimen>
    <!-- The default gap between components in a layout. -->
    <dimen name="default_gap">8dip</dimen>
    <!-- Text padding for dropdown items -->
    <dimen name="dropdownitem_text_padding_left">8dip</dimen>
    <!-- Text padding for dropdown items -->
    <dimen name="dropdownitem_text_padding_right">8dip</dimen>
    <!-- Width of the icon in a dropdown list -->
    <dimen name="dropdownitem_icon_width">32dip</dimen>
    <!-- Default width for a textview error popup -->
    <dimen name="textview_error_popup_default_width">240dip</dimen>
    <!-- Volume panel y offset -->
    <dimen name="volume_panel_top">80dp</dimen>
    <!-- Default padding to apply to AppWidgetHostViews containing widgets targeting API level 14 and up. -->
    <dimen name="default_app_widget_padding_left">8dp</dimen>
    <dimen name="default_app_widget_padding_top">8dp</dimen>
    <dimen name="default_app_widget_padding_right">8dp</dimen>
    <dimen name="default_app_widget_padding_bottom">8dp</dimen>
    <!-- Minimum width for an action button in the menu area of an action bar -->
    <dimen name="action_button_min_width">56dip</dimen>
    <!-- Maximum height for a stacked tab bar as part of an action bar -->
    <dimen name="action_bar_stacked_max_height">48dp</dimen>
    <!-- Maximum width for a stacked action bar tab. This prevents
         action bar tabs from becoming too wide on a wide screen when only
         a few are present. -->
    <dimen name="action_bar_stacked_tab_max_width">180dp</dimen>
 <!-- Size of notification text (see TextAppearance.StatusBar.EventContent) -->
    <dimen name="notification_text_size">14dp</dimen>
 <!-- Size of notification text titles (see TextAppearance.StatusBar.EventContent.Title) -->
    <dimen name="notification_title_text_size">18dp</dimen>
 <!-- Size of smaller notification text (see TextAppearance.StatusBar.EventContent.Line2, Info, Time) -->
    <dimen name="notification_subtext_size">12dp</dimen>
</resources>

主要是希望達成Sleep / Delay 的功並讓UI可更新，Android 不能套用 Java or C 的 sleep 方法，列出幾種可以取代的方法

以下幾個方法都可以達到 "Delay" 的效果 (A1 -> (wait 10s) -> A2 -> (wait 10s) -> A3...)

Thread + sleep (Thread.sleep(xxx))
Handler (handler.postDelayed(Runnable, 2000);) => Call back 到 Runnable 的 run()
Timer (timer.schedule(TimerTask, 10000);) => Call back 到 TimerTask 的 run()
Thread + Handler
Timer + Handler
SystemClock.sleep(2000);
asynctask
Handlerthread
IntentService

若要更新 UI，可以在 UI/Main thread 或者 other thread:

Thread + Handler
Timer + Handler
Timer: postInvalidate (update a view when you're not in the current UI thread.) => http://blog.csdn.net/lixinso/archive/2009/06/23/4290432.aspx
Activity.runOnUiThread(Runnable) => http://lak4cyut.blogspot.com/2011/03/android-tip-activityrunonuithread.html
View.post(Runnable)
View.postDelayed(Runnable, long)

Handler / Timer 簡單的應用區分:

Handler:

定期工作 & UI 更新 & Message dispatcher (與呼叫者處於同一線程; 可用 Message 與 Other thread 溝通)
對運行在不同線程中的多個任務進行排隊，並使用Message和Runnable對象安排這些任務。

HandlerThread:

由於採用Android Handler的post()方法並不能真正創建新的線程(參照博文：Handler.post()說明)，此處引入HandlerThread和Looper來創建新的線程。
HandlerThread繼承自Java的Thread類，HandlerThread用來創建持有一個Looper對象的線程，此Looper對象可以用來創建Handler對象。通過這種方式創建的Handler對象其start()方法一定會被調用。
Looper 直接繼承自Java的Object類，用來為一個線程維護一個消息循環隊列。線程自身默認是沒有消息隊列與其相關的；為了給線程創建消息循環隊列，要調用Looper的prepare()方法和loop()方法來創建及運行一個消息隊列。
參考:

Timer: 定期工作

Handler / Timer 使用的時機:

當 Delay or Sleep 用
類似迴圈的應用
定期觸發的定期行為

只要講到 Timer or Handler，一定會跟幾個名詞綁在一起: Thread / Handler / Timer / Timertask / Message / Looper / AsyncTask

Smart / Simple / Savory life of Jason Yeh

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