狂刷Android范例之3：读写外部存储设备
说明
狂刷Android范例系列文章开张了。每篇学习一个Android范例，将一个范例单独生成一个可运行的app，并对重点源代码进行简要分析。然后提供打包好的源代码下载。
功能
提供一个经典范例，监控Android外部存储设备状态，对公用目录，app私有目录进行读写操作，并展示在app界面上。
代码包在此，无需下载分：
http://download.csdn.net/detail/logicteamleader/8790109
来源
ReadAsset例子来自于Android-20的com.example.android.apis.content.ExternalStorage。
环境
代码运行环境：
1.ADT2014版本；
2.android:minSdkVersion=”8”；android:targetSdkVersion=”20”
3.workspace中已经生成了appcompatv7，它的版本是android-22；
4.需要两个用户权限，读取和写入外部存储。
代码
/* * 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.example.externalstorage;//Need the following import to get access to the app resources, since this//class is in a sub-package.import android.app.Activity;import android.content.BroadcastReceiver;import android.content.Context;import android.content.Intent;import android.content.IntentFilter;import android.media.MediaScannerConnection;import android.net.Uri;import android.os.Bundle;import android.os.Environment;import android.util.Log;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.Button;import android.widget.TextView;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;/*** Demonstration of ExternalStorage resources.* 此代码需添加两个权限* "android.permission.READ_EXTERNAL_STORAGE"* "android.permission.WRITE_EXTERNAL_STORAGE"*/public class ExternalStorage extends Activity { ViewGroup mLayout; /** * @author wxb * 内部类，两个Button和一个View组成 */ static class Item { View mRoot; Button mCreate; Button mDelete; } Item mExternalStoragePublicPicture; Item mExternalStoragePrivatePicture; Item mExternalStoragePrivateFile; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.external_storage); mLayout = (ViewGroup)findViewById(R.id.layout); mExternalStoragePublicPicture = createStorageControls( "Picture: getExternalStoragePublicDirectory", //得到外部存储图片的公用目录 Environment.getExternalStoragePublicDirectory( Environment.DIRECTORY_PICTURES), new View.OnClickListener() { public void onClick(View v) { createExternalStoragePublicPicture(); updateExternalStorageState(); } }, new View.OnClickListener() { public void onClick(View v) { deleteExternalStoragePublicPicture(); updateExternalStorageState(); } }); mLayout.addView(mExternalStoragePublicPicture.mRoot); mExternalStoragePrivatePicture = createStorageControls( "Picture getExternalFilesDir", //得到本app外部存储图片的私有目录 getExternalFilesDir(Environment.DIRECTORY_PICTURES), new View.OnClickListener() { public void onClick(View v) { createExternalStoragePrivatePicture(); updateExternalStorageState(); } }, new View.OnClickListener() { public void onClick(View v) { deleteExternalStoragePrivatePicture(); updateExternalStorageState(); } }); mLayout.addView(mExternalStoragePrivatePicture.mRoot); mExternalStoragePrivateFile = createStorageControls( "File getExternalFilesDir", //得到本app外部存储文件的私有目录 getExternalFilesDir(null), new View.OnClickListener() { public void onClick(View v) { createExternalStoragePrivateFile(); updateExternalStorageState(); } }, new View.OnClickListener() { public void onClick(View v) { deleteExternalStoragePrivateFile(); updateExternalStorageState(); } }); mLayout.addView(mExternalStoragePrivateFile.mRoot); startWatchingExternalStorage(); } @Override protected void onDestroy() { super.onDestroy(); stopWatchingExternalStorage(); } /** * 监测变化，改变按钮可用 */ void handleExternalStorageState(boolean available, boolean writeable) { boolean has = hasExternalStoragePublicPicture(); mExternalStoragePublicPicture.mCreate.setEnabled(writeable && !has); mExternalStoragePublicPicture.mDelete.setEnabled(writeable && has); has = hasExternalStoragePrivatePicture(); mExternalStoragePrivatePicture.mCreate.setEnabled(writeable && !has); mExternalStoragePrivatePicture.mDelete.setEnabled(writeable && has); has = hasExternalStoragePrivateFile(); mExternalStoragePrivateFile.mCreate.setEnabled(writeable && !has); mExternalStoragePrivateFile.mDelete.setEnabled(writeable && has); } BroadcastReceiver mExternalStorageReceiver; boolean mExternalStorageAvailable = false; boolean mExternalStorageWriteable = false; void updateExternalStorageState() { //得到外部存储的状态，可读？可写？ String state = Environment.getExternalStorageState(); if (Environment.MEDIA_MOUNTED.equals(state)) { mExternalStorageAvailable = mExternalStorageWriteable = true; } else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) { mExternalStorageAvailable = true; mExternalStorageWriteable = false; } else { mExternalStorageAvailable = mExternalStorageWriteable = false; } handleExternalStorageState(mExternalStorageAvailable, mExternalStorageWriteable); } /** * 监测媒体的mount和remove事件 */ void startWatchingExternalStorage() { mExternalStorageReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { Log.i("test", "Storage: " + intent.getData()); updateExternalStorageState(); } }; IntentFilter filter = new IntentFilter(); filter.addAction(Intent.ACTION_MEDIA_MOUNTED); filter.addAction(Intent.ACTION_MEDIA_REMOVED); registerReceiver(mExternalStorageReceiver, filter); updateExternalStorageState(); } void stopWatchingExternalStorage() { unregisterReceiver(mExternalStorageReceiver); } void createExternalStoragePublicPicture() { // Create a path where we will place our picture in the user's // public pictures directory. Note that you should be careful about // what you place here, since the user often manages these files. For // pictures and other media owned by the application, consider // Context.getExternalMediaDir(). File path = Environment.getExternalStoragePublicDirectory( Environment.DIRECTORY_PICTURES); File file = new File(path, "DemoPicture.jpg"); try { // Make sure the Pictures directory exists. path.mkdirs(); // Very simple code to copy a picture from the application's // resource into the external file. Note that this code does // no error checking, and assumes the picture is small (does not // try to copy it in chunks). Note that if external storage is // not currently mounted this will silently fail. InputStream is = getResources().openRawResource(R.drawable.balloons); OutputStream os = new FileOutputStream(file); byte[] data = new byte[is.available()]; is.read(data); os.write(data); is.close(); os.close(); // Tell the media scanner about the new file so that it is // immediately available to the user. MediaScannerConnection.scanFile(this, new String[] { file.toString() }, null, new MediaScannerConnection.OnScanCompletedListener() { public void onScanCompleted(String path, Uri uri) { Log.i("ExternalStorage", "Scanned " + path + ":"); Log.i("ExternalStorage", "-> uri=" + uri); } }); } catch (IOException e) { // Unable to create file, likely because external storage is // not currently mounted. Log.w("ExternalStorage", "Error writing " + file, e); } } void deleteExternalStoragePublicPicture() { // Create a path where we will place our picture in the user's // public pictures directory and delete the file. If external // storage is not currently mounted this will fail. File path = Environment.getExternalStoragePublicDirectory( Environment.DIRECTORY_PICTURES); File file = new File(path, "DemoPicture.jpg"); file.delete(); } boolean hasExternalStoragePublicPicture() { // Create a path where we will place our picture in the user's // public pictures directory and check if the file exists. If // external storage is not currently mounted this will think the // picture doesn't exist. File path = Environment.getExternalStoragePublicDirectory( Environment.DIRECTORY_PICTURES); File file = new File(path, "DemoPicture.jpg"); return file.exists(); } /** * 将一个图片拷贝到外部存储的指定文件夹中 */ void createExternalStoragePrivatePicture() { // Create a path where we will place our picture in our own private // pictures directory. Note that we don't really need to place a // picture in DIRECTORY_PICTURES, since the media scanner will see // all media in these directories; this may be useful with other // media types such as DIRECTORY_MUSIC however to help it classify // your media for display to the user. File path = getExternalFilesDir(Environment.DIRECTORY_PICTURES); File file = new File(path, "DemoPicture.jpg"); try { // Very simple code to copy a picture from the application's // resource into the external file. Note that this code does // no error checking, and assumes the picture is small (does not // try to copy it in chunks). Note that if external storage is // not currently mounted this will silently fail. InputStream is = getResources().openRawResource(R.drawable.balloons); OutputStream os = new FileOutputStream(file); byte[] data = new byte[is.available()]; is.read(data); os.write(data); is.close(); os.close(); // Tell the media scanner about the new file so that it is // immediately available to the user. MediaScannerConnection.scanFile(this, new String[] { file.toString() }, null, new MediaScannerConnection.OnScanCompletedListener() { public void onScanCompleted(String path, Uri uri) { Log.i("ExternalStorage", "Scanned " + path + ":"); Log.i("ExternalStorage", "-> uri=" + uri); } }); } catch (IOException e) { // Unable to create file, likely because external storage is // not currently mounted. Log.w("ExternalStorage", "Error writing " + file, e); } } void deleteExternalStoragePrivatePicture() { // Create a path where we will place our picture in the user's // public pictures directory and delete the file. If external // storage is not currently mounted this will fail. File path = getExternalFilesDir(Environment.DIRECTORY_PICTURES); if (path != null) { File file = new File(path, "DemoPicture.jpg"); file.delete(); } } boolean hasExternalStoragePrivatePicture() { // Create a path where we will place our picture in the user's // public pictures directory and check if the file exists. If // external storage is not currently mounted this will think the // picture doesn't exist. File path = getExternalFilesDir(Environment.DIRECTORY_PICTURES); if (path != null) { File file = new File(path, "DemoPicture.jpg"); return file.exists(); } return false; } void createExternalStoragePrivateFile() { // Create a path where we will place our private file on external // storage. File file = new File(getExternalFilesDir(null), "DemoFile.jpg"); try { // Very simple code to copy a picture from the application's // resource into the external file. Note that this code does // no error checking, and assumes the picture is small (does not // try to copy it in chunks). Note that if external storage is // not currently mounted this will silently fail. InputStream is = getResources().openRawResource(R.drawable.balloons); OutputStream os = new FileOutputStream(file); byte[] data = new byte[is.available()]; is.read(data); os.write(data); is.close(); os.close(); } catch (IOException e) { // Unable to create file, likely because external storage is // not currently mounted. Log.w("ExternalStorage", "Error writing " + file, e); } } void deleteExternalStoragePrivateFile() { // Get path for the file on external storage. If external // storage is not currently mounted this will fail. File file = new File(getExternalFilesDir(null), "DemoFile.jpg"); if (file != null) { file.delete(); } } boolean hasExternalStoragePrivateFile() { // Get path for the file on external storage. If external // storage is not currently mounted this will fail. File file = new File(getExternalFilesDir(null), "DemoFile.jpg"); if (file != null) { return file.exists(); } return false; } /** * 创建一个Item，包含一个view，两个button，以及两个button的点击事件 */ Item createStorageControls(CharSequence label, File path, View.OnClickListener createClick, View.OnClickListener deleteClick) { LayoutInflater inflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE); Item item = new Item(); item.mRoot = inflater.inflate(R.layout.external_storage_item, null); TextView tv = (TextView)item.mRoot.findViewById(R.id.label); tv.setText(label); if (path != null) { tv = (TextView)item.mRoot.findViewById(R.id.path); tv.setText(path.toString()); } item.mCreate = (Button)item.mRoot.findViewById(R.id.create); item.mCreate.setOnClickListener(createClick); item.mDelete = (Button)item.mRoot.findViewById(R.id.delete); item.mDelete.setOnClickListener(deleteClick); return item; }}