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;
}
}