[Proposal] Introduce kvs-schema

[rejasupotaro]

Overview

• Introduced kvs-schema
• Simplified SettingSwitchRowView
• Deleted PrefUtil

Problem & Solution

Currently, this app retrieves shared preferences through PrefUtil. It's a typical way but it has some problems.

Problem 1: Difficult to guess value types

PrefUtil has keys below.

public static final String KEY_CURRENT_LANGUAGE_ID = "current_language_id";
public static final String KEY_NOTIFICATION_SETTING = "notification_setting";
public static final String KEY_HEADS_UP_SETTING = "heads_up_setting";
public static final String KEY_SHOW_LOCAL_TIME = "show_local_time";

It looks that notification_setting could take json and show_local_time could take date. At first glance, I didn't understand what kind of data are stored in this app 😕

Problem 2: Need to declare similar accessors repeatedly

In this way, we need to declare new accessor when we add new value types.

public static void put(Context context, @NonNull String name, boolean value) {
    SharedPreferences.Editor edit = getPref(context).edit();
    edit.putBoolean(name, value);
    edit.apply();
}

public static void put(Context context, @NonNull String name, String value) {
    SharedPreferences.Editor edit = getPref(context).edit();
    edit.putString(name, value);
    edit.apply();
}

public static void put(Context context, @NonNull String name, int value) {
    SharedPreferences.Editor edit = getPref(context).edit();
    edit.putInt(name, value);
    edit.apply();
}

public static void put(Context context, @NonNull String name, float value) {
    SharedPreferences.Editor edit = getPref(context).edit();
    edit.putFloat(name, value);
    edit.apply();
}

public static void put(Context context, @NonNull String name, Set<String> value) {
    SharedPreferences.Editor edit = getPref(context).edit();
    edit.putStringSet(name, value);
    edit.apply();
}

...

Solution

I introduced kvs-schema that is a library to manage shared preferences. kvs-schema generates methods below statically using annotation processor.

• get*
• put*
• remove*
• has*
• set* (for Kotlin)

By this change, we can just focus on key-value management.

How to introduce kvs-schema

For the case of existing app

Step 1: Add dependencies

Add dependencies to your build.gradle.

compile 'com.github.rejasupotaro.kvs-schema:library:2.0.0'
apt 'com.github.rejasupotaro.kvs-schema:compiler:2.0.0'

Step 2: Declare schema class.

In this case, PrefUtil had keys below.

public static final String KEY_CURRENT_LANGUAGE_ID = "current_language_id";
public static final String KEY_NOTIFICATION_SETTING = "notification_setting";
public static final String KEY_HEADS_UP_SETTING = "heads_up_setting";
public static final String KEY_SHOW_LOCAL_TIME = "show_local_time";

Hence, the schema class becomes like below.

@Table("io.github.droidkaigi.confsched_preferences")
public class DefaultPrefsSchema {
    @Key("current_language_id")
    String languageId;
    @Key("notification_setting")
    boolean notificationFlag;
    @Key("heads_up_setting")
    boolean headsUpFlag;
    @Key("show_local_time")
    boolean showLocalTimeFlag;

    private static DefaultPrefs prefs;

    public static synchronized DefaultPrefs get(Context context) {
        if (prefs == null) {
            prefs = new DefaultPrefs(context);
        }
        return prefs;
    }
}

Notes 📝

• The table name should be the same as the file name. This app already has default shared preferences and its name is io.github.droidkaigi.confsched_preferences.xml (package name + "_preferences" by default). So I declared the table name as "io.github.droidkaigi.confsched_preferences".
• The key names should be the same as existing key names as well. On the other hand, you can change field names as you like.
  • I recommend to use flag suffix for boolean field like showLocalTimeFlag. kvs-schema generates method from field name. If you use is* for boolean, the getter method name becomes getIs*. It doesn't look cool 😕
• I declared DefaultPrefsSchema.get as a static synchronized method. This method may not be called from many threads at the same time. I guess that the synchronization cost is not so high.

How to add new key

Just add @Key("key_name") Type field to DefaultPrefsSchema.

[rejasupotaro]

@konifar I sent just a proposal PR. I would like to hear your opinion.

[hotchemi]

This is what I thought!

[hotchemi]

I wonder using getContext causes memory leaks cuz it just returns the Context this fragment is currently associated with. Should we use application context?

refs. https://github.com/rejasupotaro/kvs-schema/blob/06d9eaf3b7b156d7e86b6115b0d2bb68129af77c/library/src/main/java/com/rejasupotaro/android/kvs/PrefsSchema.java#L12

[rejasupotaro]

I think we don't have to use application context. Generally speaking, memory leak could occur when given context is used in different lifetime. Meanwhile in kvs-schema, DefaultPrefsSchema.get runs synchronoushly and this library doesn't hold a reference of context. CMIIW 🙇

[hotchemi]

ok!

[hotchemi]

Almost awesome! This app will be a showcase of Japanese cool libraries.

[sys1yagi]

😍

[konifar]

👀

[konifar]

Thanks for your cool solution and detailed description!
LGTM!