Android 使用SDcard进行文件的读取

  <!-- 在SDCard中创建与删除文件权限 -->
  <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
  <!-- 往SDCard写入数据权限 -->
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>   

　 1: getDataDirectory()  获取到Androi中的data数据目录
   2:getDownloadCacheDirectory()  获取到下载的缓存目录
   3:getExternalStorageDirectory()  获取到外部存储的目录 一般指SDcard
　 4:getExternalStorageState() 获取外部设置的当前状态 一般指SDcard, 

　 5:getRootDirectory()  获取到Android Root路径
   6:isExternalStorageEmulated() 返回Boolean值判断外部设置是否有效
   7:isExternalStorageRemovable()  返回Boolean值，判断外部设置是否可以移除

<span style="color:#ff0000;">Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)  代码中这句：我们对SDcard的状态进行判断,</span>

package com.jiangqq.sdcard;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class SDcardActivity extends Activity {
    private Button bt1, bt2;
    private EditText et1, et2;

    private static final String FILENAME = "temp_file.txt";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        bt1 = (Button) this.findViewById(R.id.bt1);
        bt2 = (Button) this.findViewById(R.id.bt2);
        et1 = (EditText) this.findViewById(R.id.et1);
        et2 = (EditText) this.findViewById(R.id.et2);
        bt1.setOnClickListener(new MySetOnClickListener());
        bt2.setOnClickListener(new MySetOnClickListener());
    }

    private class MySetOnClickListener implements OnClickListener {

        @Override
        public void onClick(View v) {
            File file = new File(Environment.getExternalStorageDirectory(),
                    FILENAME);
            switch (v.getId()) {
            case R.id.bt1:// 使用SDcard写操作
                if (Environment.getExternalStorageState().equals(
                        Environment.MEDIA_MOUNTED)) {

                    try {
                        FileOutputStream fos = new FileOutputStream(file);
                        fos.write(et1.getText().toString().getBytes());
                        fos.close();
                        Toast.makeText(SDcardActivity.this, "写入文件成功",
                                Toast.LENGTH_LONG).show();
                    } catch (Exception e) {
                        Toast.makeText(SDcardActivity.this, "写入文件失败",
                                Toast.LENGTH_SHORT).show();
                    }
                } else {
                    // 此时SDcard不存在或者不能进行读写操作的
                    Toast.makeText(SDcardActivity.this,
                            "此时SDcard不存在或者不能进行读写操作", Toast.LENGTH_SHORT).show();
                }
                break;

            case R.id.bt2:// 使用SDcard读操作
                if (Environment.getExternalStorageState().equals(
                        Environment.MEDIA_MOUNTED)) {
                    try {
                        FileInputStream inputStream = new FileInputStream(file);
                        byte[] b = new byte[inputStream.available()];
                        inputStream.read(b);
                        et2.setText(new String(b));
                        Toast.makeText(SDcardActivity.this, "读取文件成功",
                                Toast.LENGTH_LONG).show();
                    } catch (Exception e) {
                        Toast.makeText(SDcardActivity.this, "读取失败",
                                Toast.LENGTH_SHORT).show();
                    }
                } else {
                    // 此时SDcard不存在或者不能进行读写操作的
                    Toast.makeText(SDcardActivity.this,
                            "此时SDcard不存在或者不能进行读写操作", Toast.LENGTH_SHORT).show();
                }
                break;
            }

        }

    }

}