5.User Interface/Layout

1. Writing the XML

　　Each layout file must contain exactly one root element, which must be a View or ViewGroup object. 

　　Once you've defined the root element, you can add additional layout objects or widgets as child elements to gradually build a View hierarchy

　　　　that defines your layout.

2. Load the XML Resource

　　When you compile your application, each XML layout file is compiled into a View resource. You should load the layout resource from your

　　　　application code, in your Activity.onCreate() callback implementation. Do so by calling setContentView(), passing it the reference to your 　　

　　　　layout resource in the form of: R.layout.layout_file_name

3. Common layouts

　　

　

4. Building Layouts with an Adapter

　　When the content for your layout is dynamic or not pre-determined, you can use a layout that subclasses AdapterView to populate the

　　　　layout with views at runtime. A subclass of the AdapterView class uses an Adapter to bind data to its layout. The Adapter behaves as

　　　　a middle-man between the data source and the AdapterView layout—the Adapter retrieves the data (from a source such as an array

　　　　or a database query) and converts each entry into a view that can be added into the AdapterView layout.

　　

　　The two most common adapters are:

　　<1>ArrayAdapter

　　　　Use this adapter when your data source is an array

　　<2>SimpleCursorAdapter

　　　　Use this adapter when your data comes from a Cursor.

　　　　For example, if you want to create a list of people's names and phone numbers, you can perform a query that returns a Cursor

　　　　　　containing a row for each person and columns for the names and numbers. You then create a string array specifying

　　　　　　which columns from the Cursor you want in the layout for each result and an integer array specifying the corresponding views

　　　　　　that each column should be placed

　　　　If, during the course of your application's life, you change the underlying data that is read by your adapter, you should call

　　　　　　notifyDataSetChanged(). This will notify the attached view that the data has been changed and it should refresh itself.

　　　　

　　　　4.1 ListView

　　　　

package mirror.android.listviewtest;

import android.app.ListActivity;
import android.app.LoaderManager.LoaderCallbacks;
import android.content.CursorLoader;
import android.content.Loader;
import android.database.Cursor;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.view.View;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

public class ListViewActivity extends ListActivity implements LoaderCallbacks<Cursor>{
    
    // This is the Adapter being used to display the list's data
    private SimpleCursorAdapter mAdapter;

    // These are the Contacts rows that we will retrieve
    static final String[] PROJECTION = new String[] {ContactsContract.Data._ID,
                                                     ContactsContract.Data.DISPLAY_NAME};

    // This is the select criteria
    // = "((display_name NOTNULL) AND (display_name != '' ))"
    static final String SELECTION = "((" + 
            ContactsContract.Data.DISPLAY_NAME + " NOTNULL) AND (" +
            ContactsContract.Data.DISPLAY_NAME + " != '' ))";
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        /*// Create a progress bar to display while the list loads
        ProgressBar progressBar = new ProgressBar(this);
        progressBar.setLayoutParams(new LayoutParams(Gravity.CENTER));
        progressBar.setIndeterminate(true);
        getListView().setEmptyView(progressBar);
        
        // Must add the progress bar to the root of the layout
        ViewGroup root = (ViewGroup) findViewById(android.R.id.content);
        root.addView(progressBar);*/
        
        // For the cursor adapter, specify which columns go into which views
        String[] fromColumns = {ContactsContract.Data.DISPLAY_NAME};
        int[] toViews = {android.R.id.text1}; //// The TextView in simple_list_item_1
        
        // Create an empty adapter we will use to display the loaded data.
        // We pass null for the cursor, then update it in onLoadFinished()
        mAdapter = new SimpleCursorAdapter(this,
                                           android.R.layout.simple_list_item_1,
                                           null,
                                           fromColumns, 
                                           toViews,
                                           0);
        setListAdapter(mAdapter);
        
        // Prepare the loader.  Either re-connect with an existing one,
        // or start a new one.
        getLoaderManager().initLoader(0, null, this);
    }

    // Called when a new Loader needs to be created
    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        // Now create and return a CursorLoader that will take care of
        // creating a Cursor for the data being displayed
        return new CursorLoader(this,  
                                ContactsContract.Data.CONTENT_URI, //uri The URI
                                PROJECTION, //list of which columns to return. Passing null will return all columns, which is inefficient.
                                SELECTION, //filter declaring which rows to return, formatted as an SQL WHERE clause (excluding the WHERE itself). 
                                           //Passing null will return all rows for the given URI.
                                null,  
                                null); 
    }

    // Called when a previously created loader has finished loading
    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        // Swap the new cursor in.  (The framework will take care of closing the
        // old cursor once we return.)
        mAdapter.swapCursor(data);
    }

    // Called when a previously created loader is reset, making the data unavailable
    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        // This is called when the last Cursor provided to onLoadFinished()
        // above is about to be closed.  We need to make sure we are no
        // longer using it.
        mAdapter.swapCursor(null);
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        // Do something when a list item is clicked
        super.onListItemClick(l, v, position, id);
    }
}

　　AndroidManifest.xml add permisssion "READ_CONTRACTS"

 

 

 

　　　　

// This is the Adapter being used to display the list's data
    private SimpleCursorAdapter mAdapter;