4.Android realm数据库

1.在project的gradle里添加： classpath "io.realm:realm-gradle-plugin:3.0.0"
2.在APP的gradle里添加： apply plugin: ‘realm-android’
3.建立MyApplication，并在AndroidManifest.xml配置自定义的Application：

  public class MyApplication extends Application {
  @Override
  public void onCreate() {
    super.onCreate();
    Realm.init(this);
 //默认配置
//        RealmConfiguration config = new RealmConfiguration.Builder().build();

        //自定义配置
        RealmConfiguration config = new  RealmConfiguration.Builder()
                .name("myRealm.realm")
                .deleteRealmIfMigrationNeeded()
                .build();
        Realm.setDefaultConfiguration(config);
  }
}

4.新建一个类继承RealmObject:

public class User extends RealmObject {

    @PrimaryKey
    private String id;
    private String name;
    private String email;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String toString() {
        return "student:id="+ id +" name=" + name +"email=" + email + "\n";
    }
}

5.增删改查:

  /**
     * 增加
     */
    public void addObject() {
//        //实现方法一：事务操作
//        //类型一 ：新建一个对象，并进行存储
//        Realm realm=Realm.getDefaultInstance();
//        realm.beginTransaction();
//        User user = realm.createObject(User.class); // Create a new object
//        user.setName("John");
//        user.setEmail("john@corporation.com");
//        realm.commitTransaction();
//        //类型二：复制一个对象到Realm数据库
//        Realm realm=Realm.getDefaultInstance();
//        User user = new User("John");
//        user.setEmail("john@corporation.com");
//        realm.beginTransaction();
//        realm.copyToRealm(user);
//        realm.commitTransaction();

        //实现方法二：使用事务块
        Realm mRealm = Realm.getDefaultInstance();
        final User user = new User();
        user.setEmail("john" + number + "@corporation.com");
        user.setId(String.valueOf(number));
        user.setName("John" + number);
        try{
            mRealm.executeTransaction(new Realm.Transaction() {
                @Override
                public void execute(Realm realm) {
                    realm.copyToRealm(user);
                    tvShowResult.setText(" 增加成功:" + user.toString());
                }
            });
        }catch (Exception e){
            number++;
            e.printStackTrace();
            tvShowResult.setText(" 增加失败");
        }
    }

    /**
     * 删除
     * 同样也可以使用同addObject函数的beginTransaction和commitTransaction方法进行删除
     */
    public void deleteObject() {
        final int positon = 1;
        Realm mRealm = Realm.getDefaultInstance();
        final RealmResults<User> users = mRealm.where(User.class).findAll();
        try {
            mRealm.executeTransaction(new Realm.Transaction() {
                @Override
                public void execute(Realm realm) {
                    if (users.size() > 0) {
                        User user = users.get(positon);
                        String str = user.toString();
                        user.deleteFromRealm();
                        tvShowResult.setText("删除成功\n" + str);
//                    //删除第一个数据
//                    users.deleteFirstFromRealm();
//                    //删除最后一个数据
//                    users.deleteLastFromRealm();
//                    //删除位置为1的数据
//                    users.deleteFromRealm(1);
//                    //删除所有数据
//                    users.deleteAllFromRealm();
                    } else {
                        tvShowResult.setText("user表里无数据");
                    }
                }
            });
        }catch (Exception e){
            e.printStackTrace();
            tvShowResult.setText("删除失败");
        }
    }

    /**
     * 修改
     */
    public void updateObject() {
       try{
           String id = "1";
           String newName = "玫玫";
           Realm mRealm = Realm.getDefaultInstance();
           User user = mRealm.where(User.class).equalTo("id", id).findFirst();
           mRealm.beginTransaction();
           user.setName(newName);
           mRealm.commitTransaction();
           tvShowResult.setText("更新\n" + user.toString());
       }catch (Exception e){
           e.printStackTrace();
           tvShowResult.setText(" 更新失败");
       }
    }

    /**
     * 查询所有数据
     */
    public void queryAllObject() {
        Realm mRealm = Realm.getDefaultInstance();
        RealmResults<User> users = mRealm.where(User.class).findAll();
        /**
         * 对查询结果，按Id进行排序，只能对查询结果进行排序
         */
//        //增序排列
//        users=users.sort("id");
        //降序排列
        users = users.sort("id", Sort.DESCENDING);
        String str = "";
        for (int i = 0; i < users.size(); i++) {
            User user = users.get( i);
            str = str + user.toString();
        }
        tvShowResult.setText("查询所有数据：\n" + str);
    }

}

异步操作：

 @OnClick({R.id.tv_asy_add, R.id.tv_asy_delete, R.id.tv_asy_update, R.id.tv_asy_query})
    public void onViewClicked(View view) {
        switch (view.getId()) {
            case R.id.tv_asy_add:
                User user = new User();
                user.setEmail("john" + number + "@corporation.com");
                user.setId(String.valueOf(number));
                user.setName("John" + number);
                addUser( user );
                number++;
                break;
            case R.id.tv_asy_delete:
                String id = "1";
                deleteUser( id);
                break;
            case R.id.tv_asy_update:
                String Id = "2";
                String name = "玫玫";
                updateUser( name,Id  );
                break;
            case R.id.tv_asy_query:
                queryUser();
                break;
        }
    }

    /**
     * 增加
     * @param user
     */
    private void addUser(final User user) {
        Realm mRealm = Realm.getDefaultInstance();
        addTask=  mRealm.executeTransactionAsync(new Realm.Transaction() {
            @Override
            public void execute(Realm realm) {
                realm.copyToRealm(user);
            }
        }, new Realm.Transaction.OnSuccess() {
            @Override
            public void onSuccess() {
                tvShowResult.setText( "增加成功" + user.toString());
            }
        }, new Realm.Transaction.OnError() {
            @Override
            public void onError(Throwable error) {
                tvShowResult.setText( "增加失败");
            }
        });
    }

    /**
     * 删除
     * @param id
     */
    private void deleteUser(final String id){
        Realm mRealm = Realm.getDefaultInstance();
        final String[] str = {""};
        deleteTask=   mRealm.executeTransactionAsync(new Realm.Transaction() {
            @Override
            public void execute(Realm realm) {
                User user=realm.where(User.class).equalTo("id",id).findFirst();
                str[0] = user.toString();
                user.deleteFromRealm();
            }
        }, new Realm.Transaction.OnSuccess() {
            @Override
            public void onSuccess() {
                tvShowResult.setText( "删除成功" + str[0] );
            }
        }, new Realm.Transaction.OnError() {
            @Override
            public void onError(Throwable error) {
                tvShowResult.setText( "删除失败" + str[0] );
            }
        });

    }

    /**
     * 修改
     * @param name
     * @param id
     */
    private void updateUser(final String name, final String id){
        Realm mRealm = Realm.getDefaultInstance();
        final String[] oldStr = {""};
        final String[] newStr = {""};
        updateTask = mRealm.executeTransactionAsync(new Realm.Transaction() {
            @Override
            public void execute(Realm realm) {
                User user=realm.where(User.class).equalTo("id",id).findFirst();
                oldStr[0] = user.toString();
                user.setName(name);
                newStr[0] = user.toString();
            }
        }, new Realm.Transaction.OnSuccess() {
            @Override
            public void onSuccess() {
                tvShowResult.setText( "旧信息:" + oldStr[0] + "\n修改成功\n" + newStr[0]);
            }
        }, new Realm.Transaction.OnError() {
            @Override
            public void onError(Throwable error) {
                tvShowResult.setText( "旧信息:" + oldStr[0] + "\n修改失败");
            }
        });
    }

    /**
     * 查询所有数据
     */
    private void queryUser(){
        final Realm mRealm = Realm.getDefaultInstance();
        users = mRealm.where(User.class).findAllAsync();
        users.addChangeListener(new RealmChangeListener<RealmResults<User>>() {
            @Override
            public void onChange(RealmResults<User> element) {
                element= element.sort("id");
                List<User> datas=mRealm.copyFromRealm(element);
                String str = "";
                for (int i = 0; i <datas.size(); i++) {
                    User user = datas.get( i);
                    str = str + user.toString();
                }
                tvShowResult.setText("查询所有数据：\n" + str);
            }
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (addTask != null && !addTask.isCancelled()){
            addTask.cancel();
        }
        if (deleteTask != null && !deleteTask.isCancelled()){
            deleteTask.cancel();
        }
        if (updateTask != null && !updateTask.isCancelled()){
            updateTask.cancel();
        }
        if( users != null){
            users.removeChangeListeners();
        }
    }

}