Android Learning notes-fourth Android development component 2

Fourth Android Development component 2

1. List class components

   (1) ListView component: Lists items that need to be displayed in a vertical list

   Related properties:

   A. Android:divider used to set the separator bar for a list view, you can use color or picture resources

   B. Android:dividerheight setting the height of the separator bar

   C. android:entries specifying list items for a ListView through array resources

   D. android:footerdividersenabled sets whether the separator bar is drawn before Footerview, which defaults to true.

   E. android:headerdividersenabled sets whether the separator bar is drawn after Headerview, which defaults to true.

   (2) ListView Use steps:

   A. Drag into a ListView control and change the height to match_parent

   B. Create a new layout XML file that sets the style for each line display

   C. Create a class myadapter inherit Baseadapter

   GetView () Method: Sets the display of each row of data and the display style of each row

   GetCount () Method: Displays the number of rows, when the return value is 0 o'clock, the GetView () method is not called, and is displayed as blank

   D. Creating an Adapter object

   Myadapter adapter = new Myadapter ();

   E. Setting up an adapter for a ListView

   Listview.setadapter (adapter);

   (3) Optimization of the ListView

   Swipe up and down will constantly trigger the GetView () method

   Workaround: Reuse row layouts to reduce control lookups

   Create a class that declares several variables (the variable type and quantity are consistent with the controls contained in the layout XML file)

   Class viewholder{

   View View1;

   View View2;

   ......

   }

   Declaring member variables

   View inflate;
   

   Viewholder Holder;

   Optimization

   if (convertview==null) {

   Create a Viewholder object

   Get the Layout Converter object

   Layoutinflater inflater = Getlayoutinflate ();

   To convert a layout XML file to a layout object

   Inflate = Inflater.inflate (r.layout.listitem,null);

   Find controls

   Holder.view1 = Inflate.findviewbyid (r.id.view1);

   Holder.view2 = Inflate.findviewbyid (R.ID.VIEW2);

   Set a label

   Infalte.settag (holder);

   }else{

   Replace, re-use row layouts

   Inflate=convertview;

   Holder = (viewholder) inflate.gettag ();

   }

   To set the contents of a control based on control type

   ......

   (3) Data update

   When data changes, the adapter notifies the ListView to update the data

   Adapter.notifydatasetchanged ();

   (4) Click events for ListView

   A. Setting up tap-listening

   Listview.setonitemclicklistener (new Onitemclicklistener) {

   @Override

   public void Onitemclick (adapterview<?> parent,view view,int position,long ID) {

   ......

   }

   }

   Note: When a control with a preemption focus exists in the row layout (such as a button), the click of the ListView is invalidated

   How to resolve:

   Set properties on the control that preempted the focus in the row layout: Android:focusable = "false"

   Set in row layout so that all the controls that can preempt the focus do not preempt the focus

   android:descendantfocusability = "Blocksdescendants"

   B. Set long press Tap to listen

   Listview.setonitemlongclicklistener (new Onitemlongclicklistener) {

   @Override

   public void Onitemlongclick (adapterview<?> parent,view view,int position,long ID) {

   ......

   }

   }

3. Spinner Components: list selection box is equivalent to a common drop-down list box in a Web page

   GetSelectedItem (): Gets the selected value of the list selection box

   Onitemselectedlistener: Sets the selected event listener for the list item.

   Setdropdownviewresource (): Sets the option style for the adapter when the list box is pulled down

5. Gallery Components: Gallery View, you can display content horizontally, and you can use your finger to drag the picture to move, generally used to browse pictures. The Baseaadapter adapter is typically used to provide the Grallery component with a picture to display.

7. Imageswitcher components: picture Switcher for implementing features like "previous", "Next" in Windows Photo Viewer under Windows.                      The Viewswitcher.viewfactory interface must be implemented using Imageswitcher, and the Makeview () method is used to create a The ImageView object. For example:

   Imageswitcher.setinanimation (XXX);//Set Fade animation

   Imageswitcher.setoutanimation (XXX);//Set Fade animation

   Imageswitcher.setfactory (New Viewfactoty () {

   @Override

   Public View Makeview () {

   ImageView ImageView = new ImageView (mainactivity.this);

   return imageView;

   }

   });

   Imageswitcher.setimageresource (XXX); Set the displayed picture

Android Learning notes-fourth Android development component 2