harmony 鸿蒙Window Overview

2022-08-09
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Window Overview

Introduction

The Window module provides a mechanism for displaying multiple application UIs and allowing the end user to interact with them on the same physical screen.

For application developers, the Window module provides APIs for UI display and user interaction.
For end users, the Window module provides a way to control application UIs.
For the entire operating system, the Window module provides logic for application UI management.

Features

The Window module has the following features:

Provides a Window object to hold application and system UIs. You can load your application UIs through the window to display them to the end user.
Maintains the window relationship (overlay layers and positions). Different types of application and system windows have different default positions and overlay layers (z-index). End users can adjust the position and overlay layer of a window within a certain range.
Provides window decoration. Window decoration refers to the title bar and border of a window. The title bar usually provides the Maximize, Minimize, and Close buttons and has the default click behavior. The border can be dragged to relocate or resize the window. Window decoration is a system-level default behavior. You can enable or disable window decoration without paying attention to the implementation at the UI code layer.
Provides window animations. When a window is displayed, hidden, or switched, an animation is usually used to smooth the interaction process. This is the default behavior for application windows. You do not need to set or modify the code.
Provides guidance for input event distribution. Events are distributed based on the window status and focus. Touch and mouse events are distributed based on the window position and size, and keyboard events are distributed to the focused window. You can call APIs provided by the Window module to set whether a window is touchable and can gain focus.

Basic Concepts

Window Type

The Window module provides system windows and application windows. - A system window implements specific functionalities of the system. Examples include the volume bar, wallpaper, notification panel, status bar, and navigation bar. - An application window is related to the application display. Based on the displayed content, application windows are further classified into main windows and child windows. - A main window shows the application UI and appears on the Recents page. - A child window is an auxiliary window of an application, such as a dialog box and floating window. It is not displayed on the Recents page. Its lifecycle follows that of the main window.

Application Window Mode

The application window mode refers to the display mode of the main window when it is started. Currently, there are three application window modes: full-screen, split-screen, and freeform window. This support for multiple window modes is known as the multi-window capability.

In full-screen mode, the main window is displayed on the entire screen when it is started.
In split-screen mode, the main window occupies part of the screen when it is started, and the other part of the screen is occupied by another window. You can resize the two windows by dragging the split line between them.
In freeform window mode, the main window may come in any size or position as needed. Multiple freeform windows can be simultaneously displayed on the screen. These freeform windows are arranged on the z-axis in the sequence that they are opened or gain the focus. When a freeform window is clicked or touched, its z-index is incremented and it gains the focus.

windowMode

Working Principles

The window implementation and development vary according to the application development model, which can be FA model or stage model.

For details about the overall architecture and design ideas of the two models, see Application Models.

You are advised to use the stage model for window development.

Main Window Lifecycle in the Stage Model

In the stage model, the main window is managed and its lifecycle is maintained by the UIAbility through WindowStage. Notifications for the creation and destruction of the main window can be received via onWindowStageCreate and onWindowStageDestroy. For details, see UIAbility Lifecycle.

WindowStage also provides on(‘windowStageEvent’) to listen for its lifecycle changes.

In the stage model, when the main window of an application moves from the foreground to the background, it also triggers the UIAbility lifecycle transition. You need to pay special attention to the differences in behavior across different types of products.

On phones: When a window moves from the foreground to the background, it triggers the UIAbility to transition to the background.
On tablets:
- For applications that do not support running on 2-in-1 devices, or that can run on both phones and 2-in-1 devices, moving a window from the foreground to the background will trigger the UIAbility to transition to the background.
- For applications that do not support running on phones but do support running on 2-in-1 devices, moving a window from the foreground to the background will not trigger the UIAbility to transition to the background.
On 2-in-1 devices:
- For applications that support running on phones, moving a window from the foreground to the background will trigger the UIAbility to transition to the background.
- For applications that do not support running on phones, moving a window from the foreground to the background will not trigger the UIAbility to transition to the background.

Constraints

You cannot develop system windows in the FA model.
The application main window and child window have the following size limits: [320, 2560] in width and [240, 2560] in height, both in units of vp.
The system window has the following size limits: (0, 2560] in width and (0, 2560] in height, both in units of vp.