通过动态获取资源ID，执行接口回调-----来实现日夜模式切换

1：在res文件下，values文件   colors.xml里面

<resources>
    <color name="colorPrimary">#3F51B5color>
    <color name="colorPrimaryDark">#303F9Fcolor>
    <color name="colorAccent">#FF4081color>

    <color name="colorPrimary_night">#3b3b3bcolor>
    <color name="colorPrimaryDark_night">#383838color>
    <color name="colorAccent_night">#a72b55color>

    <color name="textColor">#FF000000color>
    <color name="textColor_night">#FFFFFFcolor>
    <color name="backgroundColor">#FFFFFFcolor>
    <color name="backgroundColor_night">#3b3b3bcolor>
resources>

2：布局

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/relativeLayout"
    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="com.bawei.Day_night_qiehuan.MainActivity">

    <Button
        android:id="@+id/btn_theme"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="切换日/夜间模式" />

    <TextView
        android:id="@+id/tv"
        android:layout_below="@id/btn_theme"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:text="通过动态获取资源ID，执行接口回调的方法" />
RelativeLayout>
3：建一个ThemeManager类

public class ThemeManager {
    // 默认是日间模式
    private static ThemeMode mThemeMode = ThemeMode.DAY;
    // 主题模式监听器
    private static List mThemeChangeListenerList = new LinkedList<>();
    // 夜间资源的缓存，key : 资源类型, 值
    private static HashMap> sCachedNightResrouces = new HashMap<>();
    // 夜间模式资源的后缀，比如日件模式资源名为：R.color.activity_bg, 那么夜间模式就为 ：R.color.activity_bg_night
    private static final String RESOURCE_SUFFIX = "_night";

    /**
     * 主题模式，分为日间模式和夜间模式
     */
    public enum ThemeMode {
        DAY, NIGHT
    }

    /**
     * 设置主题模式
     *
     * @param themeMode
     */
    public static void setThemeMode(ThemeMode themeMode) {
        if (mThemeMode != themeMode) {
            mThemeMode = themeMode;
            if (mThemeChangeListenerList.size() > 0) {
                for (OnThemeChangeListener listener : mThemeChangeListenerList) {
                    listener.onThemeChanged();
                }
            }
        }
    }

    /**
     * 根据传入的日间模式的resId得到相应主题的resId，注意：必须是日间模式的resId
     *
     * @param dayResId 日间模式的resId
     * @return 相应主题的resId，若为日间模式，则得到dayResId；反之夜间模式得到nightResId
     */
    public static int getCurrentThemeRes(Context context, int dayResId) {
        if (getThemeMode() == ThemeMode.DAY) {
            return dayResId;
        }
        // 资源名
        String entryName = context.getResources().getResourceEntryName(dayResId);
        // 资源类型
        String typeName = context.getResources().getResourceTypeName(dayResId);
        HashMap cachedRes = sCachedNightResrouces.get(typeName);
        // 先从缓存中去取，如果有直接返回该id
        if (cachedRes == null) {
            cachedRes = new HashMap<>();
        }
        Integer resId = cachedRes.get(entryName + RESOURCE_SUFFIX);
        if (resId != null && resId != 0) {
            return resId;
        } else {
            //如果缓存中没有再根据资源id去动态获取
            try {
                // 通过资源名，资源类型，包名得到资源int值
                int nightResId = context.getResources().getIdentifier(entryName + RESOURCE_SUFFIX, typeName, context.getPackageName());
                // 放入缓存中
                cachedRes.put(entryName + RESOURCE_SUFFIX, nightResId);
                sCachedNightResrouces.put(typeName, cachedRes);
                return nightResId;
            } catch (Resources.NotFoundException e) {
                e.printStackTrace();
            }
        }
        return 0;
    }

    /**
     * 注册ThemeChangeListener
     *
     * @param listener
     */
    public static void registerThemeChangeListener(OnThemeChangeListener listener) {
        if (!mThemeChangeListenerList.contains(listener)) {
            mThemeChangeListenerList.add(listener);
        }
    }

    /**
     * 反注册ThemeChangeListener
     *
     * @param listener
     */
    public static void unregisterThemeChangeListener(OnThemeChangeListener listener) {
        if (mThemeChangeListenerList.contains(listener)) {
            mThemeChangeListenerList.remove(listener);
        }
    }

    /**
     * 得到主题模式
     *
     * @return
     */
    public static ThemeMode getThemeMode() {
        return mThemeMode;
    }

    /**
     * 主题模式切换监听器
     */
    public interface OnThemeChangeListener {
        /**
         * 主题切换时回调
         */
        void onThemeChanged();
    }
}

4：现在我们来看看 MainActivity 的代码：

public class MainActivity extends AppCompatActivity implements ThemeManager.OnThemeChangeListener{
    private TextView tv;
    private Button btn_theme;
    private RelativeLayout relativeLayout;
    private ActionBar supportActionBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ThemeManager.registerThemeChangeListener(this);
        supportActionBar = getSupportActionBar();
        btn_theme = (Button) findViewById(R.id.btn_theme);
        relativeLayout = (RelativeLayout) findViewById(R.id.relativeLayout);
        tv = (TextView) findViewById(R.id.tv);
        btn_theme.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ThemeManager.setThemeMode(ThemeManager.getThemeMode() == ThemeManager.ThemeMode.DAY
                        ? ThemeManager.ThemeMode.NIGHT : ThemeManager.ThemeMode.DAY);
            }
        });
    }
    public void initTheme() {
        tv.setTextColor(getResources().getColor(ThemeManager.getCurrentThemeRes(MainActivity.this, R.color.textColor)));
        btn_theme.setTextColor(getResources().getColor(ThemeManager.getCurrentThemeRes(MainActivity.this, R.color.textColor)));
        relativeLayout.setBackgroundColor(getResources().getColor(ThemeManager.getCurrentThemeRes(MainActivity.this, R.color.backgroundColor)));
        // 设置标题栏颜色
        if(supportActionBar != null){
            supportActionBar.setBackgroundDrawable(new ColorDrawable(getResources().getColor(ThemeManager.getCurrentThemeRes(MainActivity.this, R.color.colorPrimary))));
        }
        // 设置状态栏颜色
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            Window window = getWindow();
            window.setStatusBarColor(getResources().getColor(ThemeManager.getCurrentThemeRes(MainActivity.this, R.color.colorPrimary)));
        }
    }

    @Override
    public void onThemeChanged() {
        initTheme();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        ThemeManager.unregisterThemeChangeListener(this);
    }

}