The file containing the source code shown below is located in the corresponding directory in <sdk>/samples/android-<version>/...
/*
* Copyright (C) 2010 The Android开源工程
*
* 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;
}
}