example/spinner/SpinnerActivity.java

/*
 * 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;
    }
}