Windows Hierarchy of Android window development

Many people know how to achieve a simple floating window, but few people go deep into the process behind the mechanism, because the project in the window of the interaction is more complex, encountered some pits to view a lot of information, it summarizes the floating window involved in the Knowledge points:

• Window hierarchy (How is the floating window "floating")?
• What are the restrictions on floating windows, and how can I pass the user authorization to realize the floating window function?
• The window and the user input system (how the activity receives the touch event?).

In this chapter we examine the first question: why floating windows float. Floating windows are called floating windows because they can be suspended from the application or the Desktop window, and can be separated from the activity and exist. To study the differences, let's take a look at how our most familiar activity is displayed.

How did the activity show up?

To find out the answer to this question, we first from the activity of the Setcontentview () This method of the source to start, in the activity to see the source of Setcententview:

public void setContentView(int layoutResID) { getWindow().setContentView(layoutResID); initWindowDecorActionBar(); }

GetWindow is the Mwindow variable that returns the activity, pointing to the object of a window, which is an abstract class that returns a Phonewindow object (Phonewindow is a subclass of window). Phonewindow has a Decorview object, Decorview member, which is a Framelayout,setcontentview sub-layout that will eventually be added to Decorview, This decorview is the root view of the current window, how is this root view ultimately drawn? There is a piece of code in Activitythread:

l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;                l.softInputMode |= forwardBit;                if (a.mVisibleFromClient) {                    a.mWindowAdded = true;                    wm.addView(decor, l);                }

This decorview will eventually be added to the drawing system by Windowmanager.addview, and the type is WindowManager.LayoutParams.TYPE_BASE_APPLICATION, This parameter determines the level of the z-axis of the window to be drawn, in order to avoid the thought stack too deep, here does not post the detailed source tracking process, directly to the conclusion.

Let's look at the relationship between activity and window:

Then the relationship between window and view:

Activity window Display Process:

It says how activity is displayed, in fact, how the view of activity management is displayed. Finally, let's summarize:

The view that activity is set through Setcontentview is added to Phonewindow's root view decor.

Second, window is an abstract concept, window closes a view (root view), ultimately managed by WindowManager is a view (root view) and its layoutparams, The view drawing refreshes are drawn from the underlying WindowManager (Windowmanagerglobal) with the WINDOWMANAGERSERVICEIPC interaction call.

Activity is the only component in the four components that is closely linked to the form (this is why beginners have a direct understanding of activity as the reason for drawing the interface), all the views in charge are just a window and dialog, Toast, The wallpaper does not have the same window type.

Why does the floating window "float"?

In fact, the display of activity has revealed the general interface display process, the display process of the floating window is more simple:

The students who have done the floating window should understand, why the floating window can be separated from activity and show, in essence, we are a view to the WindowManager to manage, The Layoutparams.type type determines the type of the View display window, and the level of the window (z-axis) displayed in different types is not the same. In large terms can be divided into the application window (Application_window), Sub-window (sub_window), System window (System_window) three types, the application window Z-axis range is 1~99, the child window is the range of 1001~1999, The System window is (2000~2999), so to implement the floating window we can only be implemented in the scope of the system window.

Type	Constant range	Sub-class	Constant value	Description	Example
Application_window	1~99	Type_base_application	1
		Type_application	2	application window	Most of the application windows
		Type_application_starting	3	The activity of the application displays the windows that were previously displayed by the system
		Last_application_window	99
Sub_window	1000~1999	First_sub_window	1000
		Type_application_panel	1000	Appears above the parent window, obscuring the application window below it.
		Type_application_media	1001	Appears below the parent window and is not visible if the application window does not burrow.	Surfaceview, set as media when the small window is displayed, and set as panel when full screen is displayed
		Type_application_sub_panel	1002
		Type_application_attached_dialog	1003
		Type_application_meida_overlay	1004	For the synthesis of two surfaceview, if set to media, the above Surfaceview block the surfaceview below
System_window	2000~2999	Type_status_bar	2000	Status bar at the top
		Type_search_bar	2001	Search window, only one search window can be found in the system
		Type_phone	2002	Phone window
		Type_system_alert	2003	Warning window, displayed on top of all other windows	Low Battery Alert window
		Type_keyguard	2004	Lock Screen Interface
		Type_toast	2005	Short Text Reminder Small window
		Type_system_overlay	2006	Floating window with no focus
		Type_priority_phone	2007	Emergency Phone window, can be displayed on the screen saver
		Type_system_dialog	2008	System Information pop-up window	such as the operator Information window that pops up after SIM plug-in
		Type_keyguard_dialog	2009	Popup dialog box bound to Keyguard	Sliding unlock window when lock screen
		Type_system_error	2010	System error Prompt window	ANR window
		Type_input_method	2011	IME window, crowding out the current app's space
		Type_input_method_dialog	2012	Pop-up IME window will not squeeze the current application window space, above it display
		Type_wallpaper	2013	Wallpaper
		Type_status_bar_panel	2014	The window that is pulled from the status bar
		Type_secure_system_overlay	2015	Only overlay windows that system users can create
		Type_drag	2016	Floating, draggable windows	360 security guard's floating Genie
		Type_status_bar_panel	2017
		Type_pointer	2018	Cursor
		Type_navigation_bar	2019
		Type_volume_overlay	By 2020	Volume Adjustment window
		Type_boot_progress	2021	Start progress, above all windows
		Type_hidden_nav_consumer	2022	Hidden navigation Bar
		Type_dream	2023	Screensaver animations
		Type_navigation_bar_panel	2024	Navigation Bar pop-up window	For example, apply a collection bar
		Type_universal_background	2025
		Type_display_overlay	2026	For simulating a second display device
		Type_magnification	2027	Used to enlarge Local
		Type_recents_overlay	2028	Current application window, multi-user case only displayed in user program

Windows Hierarchy of Android window development