[android] Font size of TextView in Android application changes on changing font size from native settings

I want to specify my own text size in my application, but I am having a problem doing this.

When I change the font size in the device settings, the font size of my application TextView also changes.

change the DP to sp it is good pratice for android android:textSize="18sp"

It is not a good thing to have to specify DIP or SP again by code when already defined in a dimen.xml file.

I think that the best option is to use PX when using a dimen.xml value :

tv.setTextSize(TypedValue.COMPLEX_UNIT_PX, getResources().getDimensionPixelSize(R.dimen.txt_size));

This way, you can switch from DP to SP if needed in dimen.xml file without having to change any code.

simple way to prevent the whole app from getting effected by system font size is to updateConfiguration using a base activity.

//in base activity add this code.
public  void adjustFontScale( Configuration configuration) {

    configuration.fontScale = (float) 1.0;
    DisplayMetrics metrics = getResources().getDisplayMetrics();
    WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
    wm.getDefaultDisplay().getMetrics(metrics);
    metrics.scaledDensity = configuration.fontScale * metrics.density;
    getBaseContext().getResources().updateConfiguration(configuration, metrics);

}

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    adjustFontScale( getResources().getConfiguration());
}

You can use this code:

android:textSize="32dp"

it solves your problem but you must know that you should respect user decisions. by this, changing text size from device settings will not change this value. so that's why you need to use sp instead of dp. So my suggestion is to review your app with different system font sizes(small,normal,big,...)

this may help. add the code in your custom Application or BaseActivity

/**
 * ?? getResource ??,????????
 *
 * @return
 */
@Override
public Resources getResources() {
    Resources resources = super.getResources();
    if (resources != null && resources.getConfiguration().fontScale != 1) {
        Configuration configuration = resources.getConfiguration();
        configuration.fontScale = 1;
        resources.updateConfiguration(configuration, resources.getDisplayMetrics());
    }
    return resources;
}

however, Resource#updateConfiguration is deplicated in API level 25, which means it will be unsupported some day in the future.

this solutions is with Kotlin and without using the deprecated function resources.updateConfiguration

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        adjustFontScale(resources.configuration)
    }

    private fun adjustFontScale(configuration: Configuration?) {
        configuration?.let {
            it.fontScale = 1.0F
            val metrics: DisplayMetrics = resources.displayMetrics
            val wm: WindowManager = getSystemService(Context.WINDOW_SERVICE) as WindowManager
            wm.defaultDisplay.getMetrics(metrics)
            metrics.scaledDensity = configuration.fontScale * metrics.density

            baseContext.applicationContext.createConfigurationContext(it)
            baseContext.resources.displayMetrics.setTo(metrics)

        }
    }

Observation: this is the same solution as the above but udpated with Kotlin

Use the dimension type of resources like you use string resources (DOCS).

In your dimens.xml file, declare your dimension variables:

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <dimen name="textview_height">25dp</dimen>
  <dimen name="textview_width">150dp</dimen>
  <dimen name="ball_radius">30dp</dimen>
  <dimen name="font_size">16sp</dimen>
</resources>

Then you can use these values like this:

<TextView
   android:layout_height="@dimen/textview_height"
   android:layout_width="@dimen/textview_width"
   android:textSize="@dimen/font_size"/>

You can declare different dimens.xml files for different types of screens. Doing this will guarantee the desired look of your app on different devices.

When you don't specify android:textSize the system uses the default values.

for kotlin, it works for me

priceTextView.textSize = 12f

The easiest to do so is simply to use something like the following:

android:textSize="32sp"

If you'd like to know more about the textSize property, you can check the Android developer documentation.

If units used are SP, not DP, and you want to override system font scaling, all you do is override one method in activity - see this post.

resources.updateConfiguration is deprecated and buggy (on Oreo I had issues with formatted text).

in android 8 this solution work for me

add this code in base activity

@Override
protected void attachBaseContext(Context newBase) {
    super.attachBaseContext(newBase);
    final Configuration override = new Configuration(newBase.getResources().getConfiguration());
    override.fontScale = 1.0f;
    applyOverrideConfiguration(override);
}

source https://stackoverflow.com/a/57225687/7985871

Override getResources() in Activity.

Set TextView's size in sp as usual like android:textSize="32sp"

override fun getResources(): Resources {
    return super.getResources().apply {
        configuration.fontScale = 1F
        updateConfiguration(configuration, displayMetrics)
    }
}

Also note that if the textSize is set in code, calling textView.setTextSize(X) interprets the number (X) as SP. Use setTextSize(TypedValue.COMPLEX_UNIT_DIP, X) to set values in dp.