如何知道 Activity 上哪些配置已更改？

Question

onConfigurationChanged method get called on an Activity by the system when there is(are) any changes in the configuration. This method only get called for those configurations which are defined in the manifest by the configChanges attribute.

I have multiple configurations (orientation|screenSize) defined in this configChanges attribute and I want to detect which configuration(s) has been changed so that I can do some work based on that change, how can I achieve this?

To solve this I have following code snippet:

public class MyActivity extends AppCompatActivity {
    private final String TAG = "my-activity";

    private Configuration prevConfig;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    protected void onResume () {
        super.onResume();
        prevConfig = new Configuration(getResources().getConfiguration());
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        int diff = newConfig.diff(prevConfig);

        if(((diff & ActivityInfo.CONFIG_ORIENTATION) != 0)
                || ((diff & ActivityInfo.CONFIG_SCREEN_SIZE) != 0)) {
            Log.d(TAG, "Orientation or Screen size has been changed.");
        }

        // other configuration change checking goes here

        prevConfig = new Configuration(newConfig);
    }
}

By this I can detect which configuration has been changed.

I want to know if this is the best way to achieve the goal?

Answer 1

How to know which configuration has been changed on an Activity?

To simplify the problem. You don't have to define configChanges in AndroidManifest.xml if you don't want to take control yourself when configurations changed.

The way I used is just override the onSaveInstanceState to store the Configuration before the activity being killed, and then restore it to a property like yours as prevConfig . Since android.content.res.Configuration is a kind of Parcelable. It is very easy to put it into the Bundle by calling putParcelable and recover it on onCreate .

By doing so, You will get two Configuration in onCreate() . You get the previous one from the Bundle savedInstanceState and the current the from Activity.getResources().getConfiguration() . The Configuration has a public method diff , which we can use it to return a bit mask of the differences between them.

To me, the most important thing is how to distinguish the bit mask easily. Fortunately, there is a method from the official repo we can referenced. It's static and also public. But we can't call it because of the hide annotation in JavaDoc. So, my first try was using reflection to invoke the method. It seems like the method is completely removed from the SDK due to the exception that occurred. After looking at the source. I just copy it to my own sources. Coping seems like a bad idea. But, again. It's a public static method, So it is not too difficult to copy and easy to maintain.

Here is my solution written in Kotlin.

package com.example.android.configchangeapp

import android.content.pm.ActivityInfo
import android.content.res.Configuration
import android.os.Bundle
import android.util.Log
import androidx.activity.ComponentActivity

class MainActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val config = resources.configuration
        val prevConfig = savedInstanceState?.getParcelable<Configuration>("config")
        if (prevConfig != null) {
            val diff = config.diff(prevConfig)
            val diffString = configurationDiffToString(diff)
            Log.d(TAG, "diff: $diffString")
        }
    }

    override fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)
        outState.putParcelable("config", resources.configuration)
    }

    companion object {
        const val TAG = "MainActivity"

        fun configurationDiffToString(diff: Int): String {
            val list = ArrayList<String>()
            if (diff and ActivityInfo.CONFIG_MCC != 0) {
                list.add("CONFIG_MCC")
            }
            if (diff and ActivityInfo.CONFIG_MNC != 0) {
                list.add("CONFIG_MNC")
            }
            if (diff and ActivityInfo.CONFIG_LOCALE != 0) {
                list.add("CONFIG_LOCALE")
            }
            if (diff and ActivityInfo.CONFIG_TOUCHSCREEN != 0) {
                list.add("CONFIG_TOUCHSCREEN")
            }
            if (diff and ActivityInfo.CONFIG_KEYBOARD != 0) {
                list.add("CONFIG_KEYBOARD")
            }
            if (diff and ActivityInfo.CONFIG_KEYBOARD_HIDDEN != 0) {
                list.add("CONFIG_KEYBOARD_HIDDEN")
            }
            if (diff and ActivityInfo.CONFIG_NAVIGATION != 0) {
                list.add("CONFIG_NAVIGATION")
            }
            if (diff and ActivityInfo.CONFIG_ORIENTATION != 0) {
                list.add("CONFIG_ORIENTATION")
            }
            if (diff and ActivityInfo.CONFIG_SCREEN_LAYOUT != 0) {
                list.add("CONFIG_SCREEN_LAYOUT")
            }
            if (diff and ActivityInfo.CONFIG_COLOR_MODE != 0) {
                list.add("CONFIG_COLOR_MODE")
            }
            if (diff and ActivityInfo.CONFIG_UI_MODE != 0) {
                list.add("CONFIG_UI_MODE")
            }
            if (diff and ActivityInfo.CONFIG_SCREEN_SIZE != 0) {
                list.add("CONFIG_SCREEN_SIZE")
            }
            if (diff and ActivityInfo.CONFIG_SMALLEST_SCREEN_SIZE != 0) {
                list.add("CONFIG_SMALLEST_SCREEN_SIZE")
            }
            if (diff and ActivityInfo.CONFIG_DENSITY != 0) {
                list.add("CONFIG_DENSITY")
            }
            if (diff and ActivityInfo.CONFIG_LAYOUT_DIRECTION != 0) {
                list.add("CONFIG_LAYOUT_DIRECTION")
            }
            if (diff and ActivityInfo.CONFIG_FONT_SCALE != 0) {
                list.add("CONFIG_FONT_SCALE")
            }
            if (diff and ActivityInfo.CONFIG_FONT_WEIGHT_ADJUSTMENT != 0) {
                list.add("CONFIG_AUTO_BOLD_TEXT")
            }

            return buildString {
                append("{")
                append(list.joinToString(", "))
                append("}")
            }
        }
    }
}