Android Foundation VII: UI Development

• Programming elements that need to be used
  • Views: view, the base class for visual elements, all components, views, etc. are derived from view
  • View group: ViewGroup, which is an extension of view, can include multiple sub-views
  • Fragment: Similar to the previous activity fragment, has a separate layout, but needs to be bound to the activity
  • Activity: Basic display unit for displaying the interface
• Layout
  • The layout manager is an viewgroup-based extension that controls the location of child controls and is capable of nesting
  • A layout is usually defined by a separate layout file, which separates the code from the resource and facilitates management.
  • There are many layout classes available in the
  • Android SDK that you can use to implement layouts, or you can modify these classes to create your own layouts
    • framelayout
      • simplest layout manager
      • Based on upper left corner layout
      • can change position by gravity
      • Overlay layout
      • margin Property definition location not valid
    • linearlayout
      • Linear layout
      • must define the layout direction: oritation
      • One view component can be a single row or column
      • You can define a location by margin or gravity
    • relativelayout
      • relative layout
      • The most flexible layout that allows layout to be laid out relative to screen boundary distance
      • default relative top,left layout
      • Of course sub-layouts can also be positioned relative to other components
    • GridLayout
      • Lift rectangular grid layout
      • Android4.0 later available
      • Simplified nesting of layouts
  • Defining layouts
    • Creating an XML layout file in the Layout resource folder to enable editing of layouts
    • The general root element is LinearLayout
    • Where the common attributes and values
      • Wrap_contant: Used to set the width or height value, which is calculated based on the content
      • Match_parent: Used to set the width or height value as the size of the parent element
      • Fill_parent: Used to set the width or height value, which represents the size that is allowed to be populated with the parent element, basically the same as Match_parent
      • Gravity: The position of the inner element
      • Layout_gravity: The position of itself relative to the parent element, Note that it does not work in Framelayout
      • Textallcaps: letter Case Display Flag
      • Hint: Similar to placeholder, watermark hint
      • Entries:adapter adapter padding for populating data such as list components
  • Code creation layout (although strongly recommended not to use)
    • Each layout element has a corresponding class that enables the code to construct the layout
    • instance code

    •  linearlayout linearlayout=new  linearlayout (myactivity. This  ); TextView TV  =new  TextView (myactivity. This  ); Linearlayout.layoutparams layoutparams  =new  Linearlayout.layoutparams
       (100,50 

    • use Findviewbyid to get child elements in the Contview layout file
    • layout file XML to view
      • Layoutinflator class is a tool class specifically designed to resolve layout files into view instances
      • Get Layoutinflator instances Method
        • activity in Getlayoutinflator ()
        • internal static method Layoutinflator.from (context)
        • System SERVICE Acquisition: (layoutinflator) Getsystemservice (context.layout_inflator_service);
  • layout nesting
    • padding layout is very expensive, complex interfaces require a large number of layouts to nest
    • Note redundancy to circumvent UI layouts
    • reduce unnecessary parent elements, such as framelayout child elements with only one Linearla Yout, then what's the meaning of this framelayout, and so on.
    • Layout Fill merge and include use
      • include is the use of inserting one layout into another layout
      • child layout The parent element is set to Framelayout, and the layout is more resource-intensive. You can use merge instead of the root element, and the merge will automatically delete the
    • when it is populated. Do not use too many view, too many view fills need to consume a lot of time and resources, affect the program response speed, A single non-centered view cannot be more than 80, the less the better
    • if there is a large number of view, then use Viewstub to control the view
    • viewstub
      • viewstub that are temporarily not required to display Create a view layout that you don't want to display temporarily, you can create it dynamically, or you can configure the layout file statically
      • to display the
      • by inflate or setvisibility of the viewstub instance when it needs to be displayed The difference between inflate and setvisibility
        • inflate can only be populated once, used for view fills, is empty after padding, cannot be called the inflate method for the second time, or throws an exception
        • Setvisi Bility can display the hidden control viewstub multiple times, so it is recommended that the elements in the setvisibility
      • viewstub be populated before they are fetched through Findviewbyid, otherwise they will throw an exception
  • Split layout fragment
    • fragment is a next-generation fragment component that replaces the initial activity fragment design, which is lighter than activity and useful for its full life cycle
    • Fragment can achieve different screen size devices create a flexible UI
    • Each fragment is a separate module, and is bound to the activity, the relationship is many-to-many
    • Fragment occurs after Android3.0, before 3.0 if you use
      • to create a
        • that must inherit from the Fragmentactivity
        • fragment A class that inherits from Fragment, which is android.app.Fragment after Android3.0; android.support.v4.app.Fragment
        • Populating the desired layout in Oncreateview
        • create fragment own layout file resources, you can create resources of different screen sizes, dynamically determine the resources that are populated in Oncreateview
      • fragment life cycle
        • Onattach: Bind fragment to Activity
        • onCreate: Create
        • Oncreatev Iew: Fill View
        • onactivitycreated:activity filled
        • onresume
        • onPause
        • Onsavestatein Stance
        • onStop
        • ondestoryview: Empty view
        • ondestory: Destroy
        • Ondetach: Unbind
        • fragment communication with activity

Android Foundation VII: UI Development