Usage analysis and understanding of Baseadapter in Android _android

This article analyzes the usage of Baseadapter in Android. Share to everyone for your reference, specific as follows:

Recently to do a project, the project used Listview,listview most important is binding data, this data is provided by adapter, here I rewrite the Baseadapter class to implement their own Menuadapter code as follows:

Package org.leepood.lanorder;
Import Java.io.InputStream;
Import java.util.ArrayList;
Import java.util.List;
Import Org.leepood.xmlparse.xmlParse;
Import Android.view.LayoutInflater;
Import Android.content.Context;
Import Android.util.Log;
Import Android.view.View;
Import Android.view.ViewGroup;
Import Android.widget.BaseAdapter;
Import Android.widget.TextView;
 public class Menuadapter extends Baseadapter {private layoutinflaterminflater;
  private context;
  privatelist<menu> menus;
    Publicmenuadapter (list<menu> menus,context context) {This.menus=menus;
  This.minflater =layoutinflater.from (context);
  public int GetCount () {return menus.size ();
  Public Object GetItem (intposition) {return menus.get (position);
  Public long Getitemid (intposition) {return position; Public View GetView (intposition, view Convertview, ViewGroup parent) {Menuadapterviewholder = null;//a custom class used to cache C
 Onvertview if (Convertview ==null) {     Holder=newmenuadapterview ();
      Convertview =minflater.inflate (r.layout.menu, NULL);
      Holder.name = (TextView) Convertview.findviewbyid (r.id.txtname);
      Holder.price = (TextView) Convertview.findviewbyid (R.id.txtprice);
      Holder.description = (TextView) Convertview.findviewbyid (r.id.txtdescription);
      Convertview.settag (holder);
    LOG.I ("tag", "Run Once");
    }else {holder = (Menuadapterview) convertview.gettag ();
    } holder.name.setText (string.valueof (position));
    Holder.price.setText ((String) menus.get (position). GetPrice ());
    Holder.description.setText ((String) menus.get (position). GetDescription ());
  return convertview;

 }
}

Where Baseadapter needs to be rewritten:

GetCount (), getitem (int position), getitemid (int position), getview (int position, View Convertview, ViewGroup parent)

Process Analysis:

ListView at the beginning of the drawing, the system first calls the GetCount () function, based on the length of his return, which is worth the ListView, and then, based on that length, invokes GetView () to draw each row individually. If your GetCount () returns a value of 0, the list will not show the same return 1, showing only one row. When the system displays a list, it first instantiates an adapter (this will instantiate the custom adapter). When you manually complete the adaptation, you must manually map the data, which requires overriding the GetView () method. This method is called when the system draws each row of the list. GetView () has three parameters, position represents the row to be displayed, and Covertview is the layout inflate from the layout file. We use the Layoutinflater method to extract the defined Item.xml file into a view instance for display. The individual components in the XML file are then instantiated (a simple Findviewbyid () method). This allows the data to be mapped to individual components. But in response to the Click event, the button needs to add a click listener for it to capture the click event. Now that a custom ListView is done, let's go back and look at the process. System to draw ListView, he first obtained the length of the list to be drawn, and then began to draw the first line, how to draw it? Call the GetView () function. In this function you first get a view (actually a viewgroup), and then instantiate and set up each component to display it. All right, I've finished drawing this line. Then draw the next line until the painting is finished.

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I hope this article will help you with the Android program.