Set theme color dynamically

Question

I am using themes (dynamically) in my android app, like this:

my_layout.xml (extract):

<TextView
    android:id="@+id/myItem"
    style="?my_item_style" />

attrs.xml (extract):

<attr name="my_item_style" format="reference" />

themes.xml (extract):

<style name="MainTheme.Blue">
      <item name="my_item_style">@style/my_item_style_blue</item>
</style>

<style name="MainTheme.Green">
      <item name="my_item_style">@style/my_item_style_green<item>
</style>

styles.xml (extract):

<style name="my_item_style_blue">
      <item name="android:textColor">@color/my_blue</item>
</style>

<style name="my_item_style_green">
      <item name="android:textColor">@color/my_blue</item>
</style>

So, as you can see, I am setting themes dynamically. I am using this class:

public class ThemeUtils {

  private static int sTheme;
  public final static int THEME_BLUE = 1;
  public final static int THEME_GREEN = 2;

  public static void changeToTheme(MainActivity activity, int theme) {
      sTheme = theme;
      activity.startActivity(new Intent(activity, MyActivity.class));
  }

  public static void onActivityCreateSetTheme(Activity activity)
  {
      switch (sTheme)
      {
          default:
          case THEME_DEFAULT:
          case THEME_BLUE:
              activity.setTheme(R.style.MainTheme_Blue);
              break;
          case THEME_GREEN:
              activity.setTheme(R.style.MainTheme_Green);
              break;
      }
  }

}

What I want to know, is there a way how to do this (change theme color) in code? For example, I have following code (extract):

((TextView) findViewById(R.id.myItem)).setTextColor(R.color.blue);

It can be done by some helper method, which would use switch command for available themes and return correct color for a theme. But I would like to know if there is some better, nicer and faster way.

Thanks!

Answer 1

I have finally done it using following method:

public static int getColor(String colorName) {
    Context ctx = getContext();
    switch (sTheme) {
        default:
        case THEME_DEFAULT:
            return ctx.getResources().getIdentifier("BLUE_" + colorName, "color", ctx.getPackageName());
        case THEME_BLUE:
            return ctx.getResources().getIdentifier("BLUE_" + colorName, "color", ctx.getPackageName());
        case THEME_GREEN:
            return ctx.getResources().getIdentifier("GREEN_" + colorName, "color", ctx.getPackageName());
    }
}

This returns color according to my theme (I used prefixes).

Answer 2

If I understand corectly you're looking for a way to

1. extract a style from a theme,
2. extract a value (text color) from said style.

Let's get to it.

// Extract ?my_item_style from a context/activity.
final TypedArray a = context.obtainStyledAttributes(new int[] { R.attr.my_item_style });
@StyleRes final int styleResId = a.getResourceId(0, 0);
a.recycle();

// Extract values from ?my_item_style.
final TypedArray b = context.obtainStyledAttributes(styleResId, new int[] { android.R.attr.textColor });
final ColorStateList textColors = b.getColorStateList(0);
b.recycle();

// Apply extracted values.
if (textColors != null) {
    textView.setTextColor(textColors);
}

A couple of notes:

1. TypedArray does not support getting support vector drawables and theme references in color state lists on older API levels. If you're willing to use AppCompat internal API you may want to try TintTypedArray.
2. Allocating int[] all the time is costly, make it a static final.
3. If you want to resolve multiple attributes at once the array of attributes has to be sorted! Else it crashes sometimes. <declare-styleable> generates such array and corresponding indices for you.

Answer 3

Have you check this MultipleThemeMaterialDesign demo?

SettingActivity:

@Override
protected void onCreate(Bundle savedInstanceState) {
    Preferences.applyTheme(this);
    getDelegate().installViewFactory();
    getDelegate().onCreate(savedInstanceState);
    super.onCreate(savedInstanceState);
    setToolbar();
    addPreferencesFromResource(R.xml.preferences);
    Preferences.sync(getPreferenceManager());
    mListener = new SharedPreferences.OnSharedPreferenceChangeListener() {
        @Override
        public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            Preferences.sync(getPreferenceManager(), key);
            if (key.equals(getString(R.string.pref_theme))) {
                finish();
                final Intent intent = IntentCompat.makeMainActivity(new ComponentName(
                        SettingsActivity.this, MainActivity.class));
                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | IntentCompat.FLAG_ACTIVITY_CLEAR_TASK);
                startActivity(intent);
            }
        }
    };
}

See full example for demo.