Usage records of View controls and attribute methods in Android development

Table of contents

I. Introduction

2. View class

3. Usage records of some APIs

1. Share state with parent layout

2. Set the View not to be displayed on system windows such as the status bar and navigation bar.

3. Focus can be set in touch mode

4. Set default focus

6. Focus jump

7. Display layer height

8. Offset height

9. Transparency

10. Zoom factor

11. Offset movement position

12. Rotation angle

13. View’s press sound effect

4. XML attributes of View class

5. Listener that can be set by the View class

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I. Introduction

This article mainly records some basic View API usage and description in Android development.

2. View class

ViewClasses represent the basic building blocks of user interface components. A Viewsquare area that occupies the screen and is responsible for drawing or event processing in this area. The class is the base class for all components Viewused to create interactiveUI interfaces .

All windows Vieware organized in a tree. Trees can be built by creating and assembling them in code Viewor by writing one or more XML layout files . Concrete subclasses of can serve as controls or display text, images, or other content.ViewView

Once the tree is created View, there are several common types of operations that can be performed as needed:

• Set properties . For example setting the text property for a TextView. In addition to Viewthe defined properties and methods, Viewdifferent subclasses have some unique properties and methods. Note: ViewProperties known when building the tree can XMLbe set in the layout file.
• Set focus . AndroidThe system moves focus based on user input. Use requestFocusmethods to force focus to a specific view.
• 设置Listener. Allows Viewsettings listenerto be notified when certain events of interest occur. For example, all Viewcan be setOnFocusChangeListener(android.view.View.OnFocusChangeListener)set up to track when Viewfocus is gained or lost listener. Other Viewsubclasses are provided uniquely listener. For example, one Buttoncan set up a function to monitor whether it is clicked listener.
• Set up the visualization . setVisibility(int)It can be shown or hidden through methods View.

3. Usage records of some APIs

1. Share state with parent layout

This is an easily overlooked but very important attribute. Many people have never known this attribute, so they will adopt a custom touch method to achieve the click effect and touch effect of all sub-Views under a layout. In fact, it is not needed. You only need to add this attribute to let the following child views share the state after the parent layout is clicked or the focus is selected.

android:duplicateParentState="true"

2. Set the View not to be displayed on system windows such as the status bar and navigation bar.

<!-- 用于根据状态栏等系统窗口调整视图布局。如果为 true，则调整此视图的填充以为系统窗口留出空间。仅当此视图在非嵌入式活动中时才会生效 -->
<attr name="fitsSystemWindows" format="boolean" />

3. Focus can be set in touch mode

The focus here refers to the View selection focus when the remote control or keyboard is operated.

A Boolean value that controls whether the view can receive focus in touch mode. If this is true for one view, the view can gain focus when clicked, and can maintain focus if clicked on another view that does not have this property set to true.

android:focusableInTouchMode="true"

4. Set default focus

<!-- 此视图是否为默认焦点视图。每个键盘导航集群只有一个视图可以将此属性设置为 true。 -->
<attr name="focusedByDefault" format="boolean" />

5. Focus selection and highlight

<!-- 此视图是否应在获得焦点但未在其背景中定义时使用默认焦点突出显示. -->
<attr name="defaultFocusHighlightEnabled" format="boolean" />

6. Focus jump

If you are developing a TV application, you need to set the focus selected by the remote control. Generally, you do not need to use these focus jump positions, because the Android system will automatically retrieve the next focus that needs to jump. They are only used when we specifically require a certain jump focus position to be specified.

<!-- 当下一个焦点是时，定义下一个要关注的视图。如果引用引用的视图不存在或属于不可见的层次结构的一部分，则访问引用时将产生 {@link java.lang.RuntimeException}。-->
        <attr name="nextFocusLeft" format="reference"/>

        <attr name="nextFocusRight" format="reference"/>
   
        <attr name="nextFocusUp" format="reference"/>

        <attr name="nextFocusDown" format="reference"/>

        <attr name="nextFocusForward" format="reference"/>

7. Display layer height

You can make View appear above or below other Views.

android:elevation="100dp"

8. Offset height

Same as the display layer height of "Item 7" above, which is just the offset.

android:translationZ="100dp"

9. Transparency

android:alpha="0.5"

10. Zoom factor

android:scaleX="1.5"
android:scaleY="1.5"

11. Offset movement position

android:translationY="100dp"
android:translationX="100dp"

12. Rotation angle

Set in xml file:

android:rotation="90"
android:rotationX="0.5"
android:rotationY="0.5"

Set in code:

setRotation(float类型数据);
setRotationX(float类型数据);
setRotationY(float类型数据);

13. View’s press sound effect

Set in xml file:

android:soundEffectsEnabled="true"

Set in code:

view.playSoundEffect(SoundEffectConstants.CLICK);

4. XML attributes of View class

Property name	Related methods	describe
android:accessibilityLiveRegion	setAccessibilityLiveRegion(int)	Instructs the accessibility service whether to notify the user when the View changes
android:alpha	setAlpha(float)	ViewThe transparency property of alpha, from 0(fully transparent) to 1(opaque)
android:background	setBackgroundResource(int)	drawablean element that acts as a background
android:clickable	setClickable(boolean)	Define Viewwhether this responds to click events
android:clickable	setClickable(boolean)	Define Viewwhether this responds to click events
android:contentDescription	setContentDescription(CharSequence)	Defines text that simply describes Viewthe content, often used to provide accessibility support
android:drawingCacheQuality	setDrawingCacheQuality(int)	Defines the quality of the transparent paint buffer
android:duplicateParentState		If this property is set to true, the View will obtain the drawing state (focus, pressed) from its direct parent class instead of itself.
android:fadeScrollbars	setScrollbarFadingEnabled(boolean)	Defines whether the scroll bar fades out when it is no longer useful
android:fadingEdgeLength	getVerticalFadingEdgeLength()	Set the length of the upper and lower black shadow edges of the View
android:filterTouchesWhenObscured	setFilterTouchesWhenObscured(boolean)	Specifies whether to filter touch events when the View's window is obscured by other visible windows.
android:fitsSystemWindows	setFitsSystemWindows(boolean)	ViewWhether to adjust the layout according to the system window such as the status bar
android:focusable	setFocusable(boolean)	Set whether the View can get focus
android:focusableInTouchMode	setFocusableInTouchMode(boolean)	Sets whether the View can gain focus in touch mode
android:hapticFeedbackEnabled	setHapticFeedbackEnabled(boolean)	Set Viewwhether there is tactile feedback (support for long press and other events)
android:id	setId(int)	Specify an identification name for this View, support the view.findViewById()or Activity.findViewById()method to obtain theView
android:importantForAccessibility	setImportantForAccessibility(int)	Specifies Viewthe importance of accessibility support for this
android:isScrollContainer	setScrollContainer(boolean)	Specifies whether this Viewshould be used as a scrollable container, allowing the entire window to be resized to shrink to make room for the input method.
android:keepScreenOn	setKeepScreenOn(boolean)	Specifies whether Viewthe window always keeps the screen on when it is visible
android:layerType	setLayerType(int,Paint)	ViewSpecifies the type of layer behind this (software or hardware layer)
android:layoutDirection	setLayoutDirection(int)	Specify the direction in which the layout is drawn (left to right, right to left, etc.)
android:longClickable	setLongClickable(boolean)	Specifies Viewwhether to respond to long press events
android:minHeight	setMinimumHeight(int)	Set Viewthe minimum height of the
android:minWidth	setMinimumWidth(int)	Set Viewthe minimum width of the
android:nextFocusDown	setNextFocusDownId(int)	当下一个焦点为FOCUS_DOWN时，定义获得焦点的下一个View。如果指定的View不存在或不可见，则报RuntimeException异常
android:nextFocusForward	setNextFocusForwardId(int)	当下一个焦点为FOCUS_FORWARD时，定义获得焦点的下一个View。如果指定的View不存在或不可见，则报RuntimeException异常
android:nextFocusLeft	setNextFocusLeftId(int)	当下一个焦点为FOCUS_LEFT时，定义获得焦点的下一个View。
android:nextFocusRight	setNextFocusRightId(int)	当下一个焦点为FOCUS_RIGHT时，定义获得焦点的下一个View。如果指定的View不存在或不可见，则报RuntimeException异常
android:nextFocusUp	setNextFocusUpId(int)	当下一个焦点为FOCUS_UP时，定义获得焦点的下一个View。如果指定的View不存在或不可见，则报RuntimeException异常
android:onClick		当该View被单击时触发的方法名称
android:padding	setPaddingRelative(int,int,int,int)	以像素值设置四条边的填充（View的边界和内容之间的空间）
android:paddingBottom	setPaddingRelative(int,int,int,int)	以像素值设置底边的填充
android:paddingEnd	setPaddingRelative(int,int,int,int)	以像素值设置右边的填充
android:paddingLeft	setPadding(int,int,int,int)	以像素值设置左边的填充
android:paddingRight	setPadding(int,int,int,int)	以像素值设置右边的填充
android:paddingStart	setPaddingRelative(int,int,int,int)	以像素值设置左边的填充
android:paddingTop	setPaddingRelative(int,int,int,int)	以像素值设置顶边的填充
android:requiresFadingEdge	setVerticalFadingEdgeEnabled(boolean)	定义在滚动时哪个边应该被有阴影
android:rotation	setRotation(float)	View的旋转，以度为单位
android:rotationX	setRotationX(float)	View沿x轴的旋转，以度为单位
android:rotationY	setRotationY(float)	View沿y轴的旋转，以度为单位
android:saveEnabled	setSaveEnabled(boolean)	若为false,则冻结后该View的所有状态都不会保存
android:scaleX	setScaleX(float)	View沿x轴的缩放
android:scaleY	setScaleY(float)	View沿y轴的缩放
android:scrollX		初始水平滚动偏移量，单位像素
android:scrollY		初始竖直滚动偏移量，单位像素
android:scrollbarAlwaysDrawHorizontalTrack		指定水平滚动条是否一直显示
android:scrollbarAlwaysDrawVerticalTrack		指定竖直滚动条是否一直显示
android:scrollbarDefaultDelayBeforeFade	setScrollBarDefaultDelayBeforeFade(int)	设置滚动条等待隐藏的时间，单位毫秒
android:scrollbarFadeDuration	setScrollBarFadeDuration(int)	设置滚动条隐藏的时间，单位毫秒
android:scrollbarSize	setScrollBarSize(int)	设置竖直滚动条的宽度和水平滚动条的高度
android:scrollbarStyle	setScrollBarStyle(int)	设置滚动条的样式和位置
android:scrollbarThumbHorizontal		设置水平滚动条的Thumb的drawable元素
android:scrollbarThumbVertical		设置竖直滚动条的Thumb的drawable`元素
android:scrollbarTrackHorizontal		设置水平滚动条的轨道的drawable元素
android:scrollbarTrackVertical		设置竖直滚动条的轨道的drawable元素
android:scrollbars		指定哪些滚动条应该显示
android:soundEffectsEnabled	setSoundEffectsEnabled(boolean)	指定View是否开启点击或触摸等特殊事件的声音效果
android:tag		为该View提供一个标记，通过View.getTag()或View.findViewwithTag()方法获得该View
android:textAlignment	setTextAlignment(int)	定义文本的对齐
android:textDirection	setTextDirection(int)	定义文本的方向
android:transformPivotX	setPivotX(float)	旋转或缩放依赖的坐标轴点的x坐标
android:transformPivotY	setPivotX(float)	旋转或缩放依赖的坐标轴点的y坐标
android:translationX	setTranslationX(float)	该View在x方向上的移动
android:translationY	setTranslationY(float)	The Viewmovement in the y direction
android:visibility	setVisibility(int)	Set the Viewinitial visibility

5. Listener that can be set by the View class

listener类	Setting method	describe
View.OnApplyWindowInsetsListener	setOnApplyWindowInsetsListener	Take over the Viewapplication Windows Insetspolicy
View.OnClickListener	setOnClickListener	ViewThe callback triggered when the button is clicked
View.OnCreateContextMenuListener	setOnCreateContextMenuListener	ViewCallback triggered when the context menu is being constructed
View.OnDragListener	setOnDragListener	ViewThe callback triggered when the Drag event is received
View.OnFocusChangeListener	setOnFocusChangeListener	ViewA callback triggered when the focus changes
View.OnGenericMotionListener	setOnGenericMotionListener	ViewA callback triggered when a general movement event is received
View.OnKeyListener	setOnKeyListener	ViewCallback triggered when the next hardware keyboard is pressed
View.OnLongClickListener	setOnLongClickListener	ViewA callback triggered when the button is pressed and held for a long time
View.OnSystemUiVisibilityChangeListener	setOnSystemUiVisibilityChangeListener	Callback triggered when the visibility of the system toolbar changes
View.OnTouchListener	setOnTouchListener	A callback triggered when an event Viewis receivedtouch