Android开发之自动登录功能的实现

        在我们平时使用的手机应用都可以实现只需要登陆一次账号后，第二次进入应用直接跳转到效果界面的效果，还有QQ的登陆框是如何记忆我们的隐身登陆，保存账号选项的呢，这些都是通过使用SharedPreferences共享参数效果实现的，而无须使用数据库来存储。以下我们直接看详细代码分析。

    package com.example.account.login;                import java.util.HashMap;        import java.util.Map;                import com.android.dao.MySQLiteOpenHelper;        import com.example.account.MainActivity;        import com.example.account.R;                import android.app.Activity;        import android.content.Context;        import android.content.Intent;        import android.content.SharedPreferences;        import android.database.Cursor;        import android.database.sqlite.SQLiteDatabase;        import android.database.sqlite.SQLiteOpenHelper;        import android.os.Bundle;        import android.view.View;        import android.view.View.OnClickListener;        import android.widget.Button;        import android.widget.EditText;        import android.widget.TextView;        import android.widget.Toast;                public class LoginActivity extends Activity {            private EditText e1, e2;            private SQLiteOpenHelper helper;            private boolean flag, flag2, flag3;            private HashMap<String, Object> map;                    @SuppressWarnings("unchecked")            @Override            protected void onCreate(Bundle savedInstanceState) {                super.onCreate(savedInstanceState);                setContentView(R.layout.login);                TextView textView = (TextView) this.findViewById(R.id.textView1);                e1 = (EditText) this.findViewById(R.id.editText1);                e2 = (EditText) this.findViewById(R.id.editText2);                //从共享参数获取数据                map = (HashMap<String, Object>) getMsg("login");                if (map != null && !map.isEmpty()) {                    if ((Boolean) map.get("login2")) {                        //若值为true,用户无需输入密码，直接跳转进入操作界面                        Intent intent = new Intent(LoginActivity.this,                                MainActivity.class);                        startActivity(intent);                    }                }                helper = new MySQLiteOpenHelper(this);                textView.setText("登录界面");                Button button = (Button) findViewById(R.id.button2);                button.setOnClickListener(new OnClickListener() {                            @Override                    public void onClick(View v) {                        if (!e1.getText().toString().isEmpty()                                && !e2.getText().toString().isEmpty()) {                            //从数据库获取账号信息                            SQLiteDatabase database = helper.getReadableDatabase();                            Cursor cursor = database.query("user", new String[] {                                    "username", "password" }, null, null, null, null,                                    null);                            while (cursor.moveToNext()) {                                flag = e1                                        .getText()                                        .toString()                                        .equals(cursor.getString(cursor                                                .getColumnIndex("username")));                                flag2 = e2                                        .getText()                                        .toString()                                        .equals(cursor.getString(cursor                                                .getColumnIndex("password")));                                if (flag && flag2) {                                    Intent intent = new Intent(LoginActivity.this,                                            MainActivity.class);                                    startActivity(intent);                                    //登陆跳转动画                                    overridePendingTransition(R.anim.zoomin,                                            R.anim.zoomout);                                    Toast.makeText(LoginActivity.this, "登录成功",                                            Toast.LENGTH_SHORT).show();                                    flag3 = true;                                    //登陆成功后将flag设置为ture存入共享参数中                                    HashMap<String, Object> map = new HashMap<String, Object>();                                    map.put("login2", flag3);                                    saveMsg("login", map);                                }                            }                            if (!flag3) {                                Toast.makeText(LoginActivity.this, "您输入的帐号或密码有误",                                        Toast.LENGTH_SHORT).show();                            }                        } else {                            Toast.makeText(LoginActivity.this, "请正确输入您的帐号密码",                                    Toast.LENGTH_SHORT).show();                        }                            }                        });                Button button2 = (Button) findViewById(R.id.button1);                button2.setOnClickListener(new OnClickListener() {                            @Override                    public void onClick(View v) {                                Intent intent = new Intent(LoginActivity.this,                                RegisterActivity.class);                        startActivity(intent);                            }                        });                    }           //将数据存储进入共享参数            public boolean saveMsg(String fileName, Map<String, Object> map) {                boolean flag = false;                // 一般Mode都使用private,比较安全                SharedPreferences preferences = getSharedPreferences(fileName,                        Context.MODE_PRIVATE);                SharedPreferences.Editor editor = preferences.edit();                // Map类提供了一个称为entrySet()的方法，这个方法返回一个Map.Entry实例化后的对象集。                // 接着，Map.Entry类提供了一个getKey()方法和一个getValue()方法，                // 因此，上面的代码可以被组织得更符合逻辑                for (Map.Entry<String, Object> entry : map.entrySet()) {                    String key = entry.getKey();                    Object object = entry.getValue();                    // 根据值得不同类型，添加                    if (object instanceof Boolean) {                        Boolean new_name = (Boolean) object;                        editor.putBoolean(key, new_name);                    } else if (object instanceof Integer) {                        Integer integer = (Integer) object;                        editor.putInt(key, integer);                    } else if (object instanceof Float) {                        Float f = (Float) object;                        editor.putFloat(key, f);                    } else if (object instanceof Long) {                        Long l = (Long) object;                        editor.putLong(key, l);                    } else if (object instanceof String) {                        String s = (String) object;                        editor.putString(key, s);                    }                }                flag = editor.commit();                return flag;                    }                    // 读取数据            public Map<String, ?> getMsg(String fileName) {                Map<String, ?> map = null;                // 读取数据用不到edit                SharedPreferences preferences = getSharedPreferences(fileName,                        Context.MODE_APPEND);                //Context.MODE_APPEND可以对已存在的值进行修改                map = preferences.getAll();                return map;            }                }