Android example source code file (SpinnerActivity.java)

This example Android source code file (SpinnerActivity.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

activity, android, arrayadapter, content, default_position, failed, mode_world_readable, onitemselectedlistener, os, override, position_key, property_delimiter, selection_key, sharedpreferences, spinner, spinnerprefs, string, ui, view, widget

The SpinnerActivity.java Android example source code

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.example.spinner;

import com.android.example.spinner.R;

import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemSelectedListener;

/**
 * Displays an Android spinner widget backed by data in an array. The
 * array is loaded from the strings.xml resources file.
 */
public class SpinnerActivity extends Activity {

    /**
     * Fields to contain the current position and display contents of the spinner
     */
    protected int mPos;
    protected String mSelection;

    /**
     * ArrayAdapter connects the spinner widget to array-based data.
     */
    protected ArrayAdapter<CharSequence> mAdapter;

    /**
     *  The initial position of the spinner when it is first installed.
     */
    public static final int DEFAULT_POSITION = 2;

    /**
     * The name of a properties file that stores the position and
     * selection when the activity is not loaded.
     */
    public static final String PREFERENCES_FILE = "SpinnerPrefs";

    /**
     * These values are used to read and write the properties file.
     * PROPERTY_DELIMITER delimits the key and value in a Java properties file.
     * The "marker" strings are used to write the properties into the file
     */
    public static final String PROPERTY_DELIMITER = "=";

    /**
     * The key or label for "position" in the preferences file
     */
    public static final String POSITION_KEY = "Position";

    /**
     * The key or label for "selection" in the preferences file
     */
    public static final String SELECTION_KEY = "Selection";

    public static final String POSITION_MARKER =
            POSITION_KEY + PROPERTY_DELIMITER;

    public static final String SELECTION_MARKER =
            SELECTION_KEY + PROPERTY_DELIMITER;

    /**
     * Initializes the application and the activity.
     * 1) Sets the view
     * 2) Reads the spinner's backing data from the string resources file
     * 3) Instantiates a callback listener for handling selection from the
     *    spinner
     * Notice that this method includes code that can be uncommented to force
     * tests to fail.
     *
     * This method overrides the default onCreate() method for an Activity.
     *
     * @see android.app.Activity#onCreate(android.os.Bundle)
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {

        /**
         * derived classes that use onCreate() overrides must always call the super constructor
         */
        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        Spinner spinner = (Spinner) findViewById(R.id.Spinner01);

        /*
         * Create a backing mLocalAdapter for the Spinner from a list of the
         * planets. The list is defined by XML in the strings.xml file.
         */

        this.mAdapter = ArrayAdapter.createFromResource(this, R.array.Planets,
                android.R.layout.simple_spinner_dropdown_item);

        /*
         * Attach the mLocalAdapter to the spinner.
         */

        spinner.setAdapter(this.mAdapter);

        /*
         * Create a listener that is triggered when Android detects the
         * user has selected an item in the Spinner.
         */

        OnItemSelectedListener spinnerListener = new myOnItemSelectedListener(this,this.mAdapter);

        /*
         * Attach the listener to the Spinner.
         */

        spinner.setOnItemSelectedListener(spinnerListener);


        /*
         * To demonstrate a failure in the preConditions test,
         * uncomment the following line.
         * The test will fail because the selection listener for the
         * Spinner is not set.
         */
         // spinner.setOnItemSelectedListener(null);

    }


    /**
     *  A callback listener that implements the
     *  {@link android.widget.AdapterView.OnItemSelectedListener} interface
     *  For views based on adapters, this interface defines the methods available
     *  when the user selects an item from the View.
     *
     */
    public class myOnItemSelectedListener implements OnItemSelectedListener {

        /*
         * provide local instances of the mLocalAdapter and the mLocalContext
         */

        ArrayAdapter<CharSequence> mLocalAdapter;
        Activity mLocalContext;

        /**
         *  Constructor
         *  @param c - The activity that displays the Spinner.
         *  @param ad - The Adapter view that
         *    controls the Spinner.
         *  Instantiate a new listener object.
         */
        public myOnItemSelectedListener(Activity c, ArrayAdapter<CharSequence> ad) {

          this.mLocalContext = c;
          this.mLocalAdapter = ad;

        }

        /**
         * When the user selects an item in the spinner, this method is invoked by the callback
         * chain. Android calls the item selected listener for the spinner, which invokes the
         * onItemSelected method.
         *
         * @see android.widget.AdapterView.OnItemSelectedListener#onItemSelected(
         *  android.widget.AdapterView, android.view.View, int, long)
         * @param parent - the AdapterView for this listener
         * @param v - the View for this listener
         * @param pos - the 0-based position of the selection in the mLocalAdapter
         * @param row - the 0-based row number of the selection in the View
         */
        public void onItemSelected(AdapterView<?> parent, View v, int pos, long row) {

            SpinnerActivity.this.mPos = pos;
            SpinnerActivity.this.mSelection = parent.getItemAtPosition(pos).toString();
            /*
             * Set the value of the text field in the UI
             */
            TextView resultText = (TextView)findViewById(R.id.SpinnerResult);
            resultText.setText(SpinnerActivity.this.mSelection);
        }

        /**
         * The definition of OnItemSelectedListener requires an override
         * of onNothingSelected(), even though this implementation does not use it.
         * @param parent - The View for this Listener
         */
        public void onNothingSelected(AdapterView<?> parent) {

            // do nothing

        }
    }

    /**
     * Restores the current state of the spinner (which item is selected, and the value
     * of that item).
     * Since onResume() is always called when an Activity is starting, even if it is re-displaying
     * after being hidden, it is the best place to restore state.
     *
     * Attempts to read the state from a preferences file. If this read fails,
     * assume it was just installed, so do an initialization. Regardless, change the
     * state of the spinner to be the previous position.
     *
     * @see android.app.Activity#onResume()
     */
    @Override
    public void onResume() {

        /*
         * an override to onResume() must call the super constructor first.
         */

        super.onResume();

        /*
         * Try to read the preferences file. If not found, set the state to the desired initial
         * values.
         */

        if (!readInstanceState(this)) setInitialState();

        /*
         * Set the spinner to the current state.
         */

        Spinner restoreSpinner = (Spinner)findViewById(R.id.Spinner01);
        restoreSpinner.setSelection(getSpinnerPosition());

    }

    /**
     * Store the current state of the spinner (which item is selected, and the value of that item).
     * Since onPause() is always called when an Activity is about to be hidden, even if it is about
     * to be destroyed, it is the best place to save state.
     *
     * Attempt to write the state to the preferences file. If this fails, notify the user.
     *
     * @see android.app.Activity#onPause()
     */
    @Override
    public void onPause() {

        /*
         * an override to onPause() must call the super constructor first.
         */

        super.onPause();

        /*
         * Save the state to the preferences file. If it fails, display a Toast, noting the failure.
         */

        if (!writeInstanceState(this)) {
             Toast.makeText(this,
                     "Failed to write state!", Toast.LENGTH_LONG).show();
          }
    }

    /**
     * Sets the initial state of the spinner when the application is first run.
     */
    public void setInitialState() {

        this.mPos = DEFAULT_POSITION;

    }

    /**
     * Read the previous state of the spinner from the preferences file
     * @param c - The Activity's Context
     */
    public boolean readInstanceState(Context c) {

        /*
         * The preferences are stored in a SharedPreferences file. The abstract implementation of
         * SharedPreferences is a "file" containing a hashmap. All instances of an application
         * share the same instance of this file, which means that all instances of an application
         * share the same preference settings.
         */

        /*
         * Get the SharedPreferences object for this application
         */

        SharedPreferences p = c.getSharedPreferences(PREFERENCES_FILE, MODE_WORLD_READABLE);
        /*
         * Get the position and value of the spinner from the file, or a default value if the
         * key-value pair does not exist.
         */
        this.mPos = p.getInt(POSITION_KEY, SpinnerActivity.DEFAULT_POSITION);
        this.mSelection = p.getString(SELECTION_KEY, "");

        /*
         * SharedPreferences doesn't fail if the code tries to get a non-existent key. The
         * most straightforward way to indicate success is to return the results of a test that
         * SharedPreferences contained the position key.
         */

          return (p.contains(POSITION_KEY));

        }

    /**
     * Write the application's current state to a properties repository.
     * @param c - The Activity's Context
     *
     */
    public boolean writeInstanceState(Context c) {

        /*
         * Get the SharedPreferences object for this application
         */

        SharedPreferences p =
                c.getSharedPreferences(SpinnerActivity.PREFERENCES_FILE, MODE_WORLD_READABLE);

        /*
         * Get the editor for this object. The editor interface abstracts the implementation of
         * updating the SharedPreferences object.
         */

        SharedPreferences.Editor e = p.edit();

        /*
         * Write the keys and values to the Editor
         */

        e.putInt(POSITION_KEY, this.mPos);
        e.putString(SELECTION_KEY, this.mSelection);

        /*
         * Commit the changes. Return the result of the commit. The commit fails if Android
         * failed to commit the changes to persistent storage.
         */

        return (e.commit());

    }

    public int getSpinnerPosition() {
        return this.mPos;
    }

    public void setSpinnerPosition(int pos) {
        this.mPos = pos;
    }

    public String getSpinnerSelection() {
        return this.mSelection;
    }

    public void setSpinnerSelection(String selection) {
        this.mSelection = selection;
    }
}