<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <EditText
        android:id="@+id/et_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入用户名" />

    <EditText
        android:id="@+id/et_pwd"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入密码" />

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <CheckBox
            android:id="@+id/cb"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="保存密码" />

        <Button
            android:id="@+id/btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentRight="true"
            android:layout_toRightOf="@id/cb"
            android:text="登录" />
    </RelativeLayout>
</LinearLayout>

    public void ReadFile() {
        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
            File sdcardDir = Environment.getExternalStorageDirectory();
            try {
                FileInputStream fis = new FileInputStream(sdcardDir.getCanonicalPath() + "/info.txt");
                BufferedReader br = new BufferedReader(new InputStreamReader(fis));
                StringBuilder sb = new StringBuilder();
                String line = null;
                while ((line = br.readLine()) != null) {
                    sb.append(line);
                }
                br.close();
                Log.e(TAG, "ReadFile: " + sb.toString());
                HashMap<String, String> map = new HashMap<>();
                final String[] split = sb.toString().split("##");
                int length = split.length;
                Log.e(TAG, "onCreate: " + split.length);
                map.put("name", split[0]);
                map.put("pwd", split[1]);
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        mEtName.setText(split[0]);
                        mEtPwd.setText(split[1]);
                        mCb.setChecked(true);
                    }
                });
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public boolean writeFile(String name, String pwd) {
        String content = name + "##" + pwd;
        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
            File sdcarDir = Environment.getExternalStorageDirectory();
            try {
                FileOutputStream fos = new FileOutputStream(sdcarDir.getCanonicalPath() + "/info.txt");
                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();
                return true;
/*
等价于
new BufferedWriter(
new OutputStreamWriter(
new FileOutputStream(sdcardDir.getCanonicalPath()+"wenjianming")))
.write("sfsd");
但不知道怎么close哈哈
*/
            } catch (IOException e) {
                e.printStackTrace();
                return false;
            }
        }
        return false;
    }