第5天SD卡操作
阿新 • • 發佈:2018-12-26
第5天SD卡操作
SD卡操作
一.手機記憶體圖
2.SD卡介紹:
1.一般手機檔案管理 根路徑 /storage/emulated/0/或者/mnt/shell/emulated/0
2.重要程式碼:
(1)Environment.getExternalStorageState();// 判斷SD卡是否
(2)Environment.getExternalStorageDirectory(); 獲取SD卡的根目錄
(3)Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES); 獲取SD卡公開目錄pictures資料夾
3.必須要新增讀寫SD卡的許可權
三.程式碼
(1)新增讀寫SD卡的 許可權
(2)FileUtils.java:四個方法:實現向SD卡中讀寫Bitmap圖片和json字串
public class FileUtils {
//方法1:向SD卡中寫json串
public static void write_json(String json) {
//判斷是否掛載
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
//獲取SD卡根路徑:mnt/shell/emulated/0
File file=Environment.getExternalStorageDirectory();
FileOutputStream out=null;
try {
//建立輸出流
out= new FileOutputStream(new File(file,"json.txt"));
out.write(json.getBytes());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
if(out!=null){
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
//方法2:從SD卡中讀取json串
public static String read_json() {
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
File file = Environment.getExternalStorageDirectory();
FileInputStream inputStream = null;
StringBuffer sb=new StringBuffer();
try {
inputStream=new FileInputStream(new File(file,"json.txt"));
byte[] b=new byte[1024];
int len=0;
while((len=inputStream.read(b))!=-1){
sb.append(new String(b,0,len));
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
if(inputStream!=null){
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return sb.toString();
}else{
return "";
}
}
//方法3:從SD卡中讀取一張圖片
public static Bitmap read_bitmap(String filename) {//filename圖片名字
Bitmap bitmap=null;
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
File file=Environment.getExternalStorageDirectory();
File file1 = new File(file, filename);
//BitmapFactory可以直接根據SD卡圖片路徑轉成一個bitmap物件
bitmap= BitmapFactory.decodeFile(file1.getAbsolutePath());
}
return bitmap;
}
//方法4:網路下載一張圖片儲存到SD卡中
public static void write_bitmap(String url) {//網址
new MyTask().execute(url);
}
static class MyTask extends AsyncTask<String,String,String> {
@Override
protected String doInBackground(String... strings) {
FileOutputStream out=null;
InputStream inputStream=null;//網路連線的輸入流
HttpURLConnection connection=null;//向SD卡寫的輸出流
try {
URL url= new URL(strings[0]);
connection= (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(5*1000);
connection.setReadTimeout(5*1000);
if (connection.getResponseCode()==200){
inputStream = connection.getInputStream();
//TODO 獲取SD卡的路徑
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {//是否掛載
File file = Environment.getExternalStorageDirectory();
out = new FileOutputStream(new File(file,"xiaoyueyue.jpg"));
byte[] bytes=new byte[1024];
int len=0;
while((len=inputStream.read(bytes))!=-1){
out.write(bytes,0,len);
}
}
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally {
//關流
if(out!=null){
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(inputStream!=null){
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(connection!=null){
connection.disconnect();
}
}
return null;
}
}
}