java - findPreference() 返回 null

Question

我正在尝试实用地将 SwitchPreferenceCompat 的切换开关更改为 true 和 false。但是，在 SettingsFragment 类中，方法 ammendSwitchPreferenceSetting() 首选项变量始终为 null，但是如果我从 onCreatePreferences() 中调用此方法，它将起作用，但我需要在其他地方调用它。

import android.os.Bundle;

import androidx.appcompat.app.ActionBar;
import androidx.appcompat.app.AppCompatActivity;
import androidx.preference.CheckBoxPreference;
import androidx.preference.PreferenceFragmentCompat;
import androidx.preference.SwitchPreferenceCompat;

public class SettingsActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.settings_activity);

        getSupportFragmentManager()
                .beginTransaction()
                .replace(R.id.settings, new SettingsFragment())
                .commit();
        ActionBar actionBar = getSupportActionBar();

        //will allow the user to go back to parent page of the application
        if (actionBar != null) {
            actionBar.setDisplayHomeAsUpEnabled(true);
        }
    }

    public static class SettingsFragment extends PreferenceFragmentCompat {
        @Override
        public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
            setPreferencesFromResource(R.xml.root_preferences, rootKey);
        }

        public void ammendSwitchPreferenceSetting(String key, boolean value){
            //is always null for some reason
            SwitchPreferenceCompat preference =  findPreference(key);
            preference.setChecked(value);
        }

    }
}

 <SwitchPreferenceCompat
            android:enabled="true"
            android:summary="some summary"
            app:defaultValue="true"
            app:key="NetworkType"
            app:title="some title" />

然后我从另一个类调用它

SettingsActivity.SettingsFragment settingsFragment = new SettingsActivity.SettingsFragment();
settingsFragment.ammendSwitchPreferenceSetting("NetworkType", false);

Answer 1

我正在使用 Kotlin，这就是我更改开关值的方法。

val sharedpref = PreferenceManager.getDefaultSharedPreferences(this).edit()
sharedpref.putBoolean("NetworkType",false).apply()

在java中，会是这样的

sharedpref prefs = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
sharedpref.Editor editor = prefs.edit();
editor.putBoolean("NetworkType",false);
editor.apply();

Note: I didn't teste this Java version, but the concept is like that.