数据操作工具类——sd卡

public class SDFileHelper {

private Context context;

public SDFileHelper() {
}

public SDFileHelper(Context context) {
super();
this.context = context;
}

//往SD卡写入文件的方法
public void savaFileToSD(String filename, String filecontent) throws Exception {
//如果手机已插入sd卡,且app具有读写sd卡的权限
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
filename = Environment.getExternalStorageDirectory().getCanonicalPath() + "/" + filename;
//这里就不要用openFileOutput了,那个是往手机内存中写数据的
FileOutputStream output = new FileOutputStream(filename);
output.write(filecontent.getBytes());
//将String字符串以字节流的形式写入到输出流中
output.close();
//关闭输出流
} else Toast.makeText(context, "SD卡不存在或者不可读写", Toast.LENGTH_SHORT).show();
}

//读取SD卡中文件的方法
//定义读取文件的方法:
public String readFromSD(String filename) throws IOException {
StringBuilder sb = new StringBuilder("");
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
filename = Environment.getExternalStorageDirectory().getCanonicalPath() + "/" + filename;
//打开文件输入流
FileInputStream input = new FileInputStream(filename);
byte[] temp = new byte[1024];

int len = 0;
//读取文件内容:
while ((len = input.read(temp)) > 0) {
sb.append(new String(temp, 0, len));
}
//关闭输入流
input.close();
}
return sb.toString();
}

}
接着MainActivity.java实现相关逻辑：
public class MainActivity extends AppCompatActivity implements View.OnClickListener{

private EditText editname;
private EditText editdetail;
private Button btnsave;
private Button btnclean;
private Button btnread;
private Context mContext;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mContext = getApplicationContext();
bindViews();
}

private void bindViews() {
editname = (EditText) findViewById(R.id.edittitle);
editdetail = (EditText) findViewById(R.id.editdetail);
btnsave = (Button) findViewById(R.id.btnsave);
btnclean = (Button) findViewById(R.id.btnclean);
btnread = (Button) findViewById(R.id.btnread);

btnsave.setOnClickListener(this);
btnclean.setOnClickListener(this);
btnread.setOnClickListener(this);
}

@Override
public void onClick(View v) {
switch (v.getId()){
case R.id.btnclean:
editdetail.setText("");
editname.setText("");
break;
case R.id.btnsave:
String filename = editname.getText().toString();
String filedetail = editdetail.getText().toString();
SDFileHelper sdHelper = new SDFileHelper(mContext);
try
{
sdHelper.savaFileToSD(filename, filedetail);
Toast.makeText(getApplicationContext(), "数据写入成功", Toast.LENGTH_SHORT).show();
}
catch(Exception e){
e.printStackTrace();
Toast.makeText(getApplicationContext(), "数据写入失败", Toast.LENGTH_SHORT).show();
}
break;
case R.id.btnread:
String detail = "";
SDFileHelper sdHelper2 = new SDFileHelper(mContext);
try
{
String filename2 = editname.getText().toString();
detail = sdHelper2.readFromSD(filename2);
}
catch(IOException e){e.printStackTrace();}
Toast.makeText(getApplicationContext(), detail, Toast.LENGTH_SHORT).show();
break;
}
}
}
最后别忘记在AndroidManifest.xml写上读写SD卡的权限哦！
<!-- 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"/>