Android存储（四）：读写SD卡的文件

Android 读写SD卡的文件

要读写SD卡上的文件，首先需要判断是否存在SD卡：

    Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED);

然后才能读写SD卡上的文件，调用Environment的getExternalStorageDirectory()方法获取外部存储器(SD卡)的目录。使用FileInputStream、FileOutputStream、FileReader或FileWriter读、写SD卡里的文件。

需要注意是要添加相应的权限。

读文件的代码：

private String read(){        try {            //如果手机插入了SD卡，而且应用程序具有访问SD的权限            if (Environment.getExternalStorageState() .equals(Environment.MEDIA_MOUNTED)) {                //获取SD卡对应的存储目录                File sdCardDir = Environment.getExternalStorageDirectory();                //获取指定文件对应的输入流                FileInputStream fis = new FileInputStream(sdCardDir                    .getCanonicalPath()    + FILE_NAME);                //将指定输入流包装成BufferedReader                BufferedReader br = new BufferedReader(new                    InputStreamReader(fis));                StringBuilder sb = new StringBuilder("");                String line = null;                while((line = br.readLine()) != null){                    sb.append(line);                }                return sb.toString();            }        }        catch (Exception e)        {            e.printStackTrace();        }        return null;    }

使用RandomAccessFile向SD卡指定文件追加数据

    private void write(String content) {        try {                //如果手机插入了SD卡，而且应用程序具有访问SD的权限            if (Environment.getExternalStorageState()                .equals(Environment.MEDIA_MOUNTED))            {                //获取SD卡的目录                File sdCardDir = Environment.getExternalStorageDirectory();                File targetFile = new File(sdCardDir.getCanonicalPath()                    + FILE_NAME);                //以指定文件创建    RandomAccessFile对象                RandomAccessFile raf = new RandomAccessFile(                    targetFile , "rw");                //将文件记录指针移动到最后                raf.seek(targetFile.length());                // 输出文件内容                raf.write(content.getBytes());                raf.close();            }        }        catch (Exception e)        {            e.printStackTrace();        }    }

FileOutputStream会把原来的数据清空，然后重新写入数据

private void write(String content){    try {            //如果手机插入了SD卡，而且应用程序具有访问SD的权限        if (Environment.getExternalStorageState() .equals(Environment.MEDIA_MOUNTED))  {                     FileOutputStream fos = new FileOutputStream(Environment.getExternalStorageDirectory());                OutputStreamWriter osw = new OutputStreamWriter(fos);                BufferedWriter bw = new BufferedWriter(osw);                bw.write(content); // content为你需要写入的字符串                bw.close();            }    }    catch (Exception e) {        e.printStackTrace();    }}

实例：SD卡文件浏览器

布局文件：

layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>

layout/line.xml

<?xml version="1.0" encoding="utf-8"?>

MainActivity

import android.os.Bundle;import android.os.Environment;import android.support.v7.app.AppCompatActivity;import android.view.View;import android.widget.AdapterView;import android.widget.Button;import android.widget.ListView;import android.widget.SimpleAdapter;import android.widget.TextView;import android.widget.Toast;import java.io.File;import java.io.IOException;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class MainActivity extends AppCompatActivity {    private ListView mListView;    private TextView mTextView;    //记录当前的父文件夹    private File mCurrentParent;    //记录当前路径下的所有文件的文件数组    File[] mCurrentFiles;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mListView = (ListView) findViewById(R.id.list);        mTextView = (TextView) findViewById(R.id.path);        //获取系统的SD卡的目录        File root = new File(String.valueOf(Environment.getExternalStorageDirectory()));        //如果SD卡存在        if (root.exists()) {            mCurrentParent = root;            mCurrentFiles = root.listFiles();            //使用当前目录下的全部文件、文件夹来填充ListView            inflateListView(mCurrentFiles);        }        mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {            @Override            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {                if (mCurrentFiles[position].isFile()) {                    return;                }                File[] tmp = mCurrentFiles[position].listFiles();                if (tmp == null || tmp.length == 0) {                    Toast.makeText(MainActivity.this, "当前路径不可访问或该路径下没有文件", Toast.LENGTH_SHORT).show();                } else {                    mCurrentParent = mCurrentFiles[position];                    mCurrentFiles = tmp;                    inflateListView(mCurrentFiles);                }            }        });        //获取上一级目录的按钮        Button parent = (Button) findViewById(R.id.parent);        parent.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                try {                    if (!mCurrentParent.getCanonicalFile().equals("/mnt/shell/emulated/0")) {                        mCurrentParent = mCurrentParent.getParentFile();                        mCurrentFiles = mCurrentParent.listFiles();                        inflateListView(mCurrentFiles);                    }                } catch (IOException e) {                    e.printStackTrace();                }            }        });    }    private void inflateListView(File[] files) {        //创建一个List集合,List集合的元素是Map        List> listItems = new ArrayList<>();        for (int i = 0; i < files.length; i++) {            Map listItem = new HashMap<>();            if (files[i].isDirectory()) {                listItem.put("icon", R.drawable.folder);            } else {                listItem.put("icon", R.drawable.file);            }            listItem.put("fileName", files[i].getName());            listItems.add(listItem);        }        //创建一个SimpleAdapter        SimpleAdapter simpleAdapter = new SimpleAdapter(this, listItems, R.layout.line, new String[]{"icon", "fileName"}, new int[]{R.id.icon, R.id.file_name});        mListView.setAdapter(simpleAdapter);        try {            mTextView.setText("当前路径为:" + mCurrentParent.getCanonicalPath());        } catch (IOException e) {            e.printStackTrace();        }    }}

Android 读写SD卡的文件

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