Login Example

1.activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/user_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/user_name"
        android:layout_alignParentTop="true"
        android:text="@string/user_text"
        android:textSize="20sp" />
    <EditText
        android:id="@+id/user_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/user_text"
        android:inputType="text"
        android:hint="@string/user_alert"
        android:textSize="20sp" />
   
    <TextView
        android:id="@+id/pass_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/user_text"
        android:layout_alignBottom="@+id/pwd"
        android:text="@string/pass_text"
        android:textSize="20sp" />
    <EditText
        android:id="@+id/pwd"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/user_name"
        android:layout_toRightOf="@+id/pass_text"
        android:inputType="textPassword"
        android:hint="@string/pass_alert"
        android:textSize="20sp" />
    <CheckBox android:id="@+id/check_save"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/pass_text"
        android:text="@string/check_save"
        android:textSize="20sp" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/check_save"
        android:text="@string/login_text"
        android:onClick="onLoginCeck"
        android:textSize="20sp"
        />

</RelativeLayout>

2.MainActivity.java
package com.example.loginfile;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

//從文件中取出用戶名及密碼,并寫入到畫面中。
try {
File file = new File(getFilesDir(), "login.txt");
//文件存在且不為空,才取用戶名與密碼.
if(file.exists() && file.length() > 0 ){
char buffer[] = new char[1024];
FileReader rd = new FileReader(file);
int len = rd.read(buffer);
rd.close();
String data = new String(buffer,0,len);
String buff[] = data.split(";");

if(buff.length > 0){
String account = buff[0];
String pass = buff[1];
//System.out.println("account=" +account + "--pass=" + pass);
//將用戶名與密碼set到輸入框中.
((EditText)findViewById(R.id.user_name)).setText(account);
((EditText)findViewById(R.id.pwd)).setText(pass);
}
}}
catch(IOException e){
e.printStackTrace();
}
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}

public void onLoginCeck(View v) throws IOException{
//此方法主要是把用戶名與密碼保存到txt文件中.
EditText et_userno = (EditText) findViewById(R.id.user_name);
String user_no = et_userno.getText().toString();
EditText et_pass = (EditText) findViewById(R.id.pwd);
String pwd = et_pass.getText().toString();
//System.out.println("user_no=" + user_no);
//System.out.println("pwd=" + pwd);
//用戶與密碼不能為空.
if(user_no == null || "".equalsIgnoreCase(user_no)){
Toast.makeText(getApplicationContext(), "user name can't empty.", Toast.LENGTH_LONG).show();
return;
}
if(pwd == null || "".equalsIgnoreCase(pwd)){
Toast.makeText(getApplicationContext(), "passworld can not empty.", Toast.LENGTH_LONG).show();
return;
}
System.out.println("after user_no empty.");
//保存復選框選中,則將用戶及密碼保存到txt文件.
File file = new File(getFilesDir(), "login.txt");
CheckBox cb = (CheckBox) findViewById(R.id.check_save);
if(cb.isChecked()){
FileWriter wt = new FileWriter(file);
wt.write(user_no + ";" + pwd);
wt.close();
}
}

}

3.strings.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">loginFile</string>
    <string name="action_settings">Settings</string>
    <string name="user_text">用户名称：</string>
    <string name="user_alert">please input account</string>
    <string name="pass_text">用户密码：</string>
    <string name="pass_alert">input passworld</string>
<string name="check_save">是否保存用户及密码</string>
<string name="login_text">登錄</string>
</resources>