I have two images (not colors) called black and white. I've written this code so far:

public class MainActivity extends AppCompatActivity
{
    View parentView;
    SwitchCompat switchCompat;

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

        switchCompat = findViewById(R.id.switchCompat);
        parentView = findViewById(R.id.parentView);

        SharedPreferences prefs = getSharedPreferences("save", MODE_PRIVATE);
        switchCompat.setChecked(prefs.getBoolean("value", false);
        
        switchCompat.setOnClickListener(view -> {
            if(switchCompat.isChecked()) {
               parentView.setImageResource(R.drawable.black);
               SharedPreferences.Editor ed = getSharedPreferences("save", MODE_PRIVATE);
               ed.putBoolean("value", true);
               ed.apply();
               switchCompat.setChecked(true);
            } else {
               parentView.setImageResource(R.drawable.white);
               SharedPreferences.Editor ed = getSharedPreferences("save", MODE_PRIVATE);
               ed.putBoolean("value", false);
               ed.apply();
               switchCompat.setChecked(false);
            }
        });
    }

Default background is white. As you see, if the user check switch on the background should be black, but this doesn't work. Do you know any solution?

CodePudding user response：

You needn't set the SwitchCompat if its changed, its redundant. Also SharedPreferences.Editor was initialized wrong. Try this

public class MainActivity extends AppCompatActivity implements CompoundButton.OnCheckedChangeListener {

    View parentView;
    SwitchCompat switchCompat;
    SharedPreferences prefs;

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

        switchCompat = findViewById(R.id.switchCompat);
        parentView = findViewById(R.id.parentView);

        prefs = getSharedPreferences("save", MODE_PRIVATE);
        switchCompat.setChecked(prefs.getBoolean("value", false));
        if (prefs.getBoolean("value", false)) { 
            parentView.setBackgroundResource(R.drawable.black);
         } else {
            parentView.setBackgroundResource(R.drawable.white);
         }
        switchCompat.setOnCheckedChangeListener(this);
    }

    @Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            if(buttonView.getId() == R.id.switchCompat) {
                if(isChecked) {
                  parentView.setImageResource(R.drawable.black);
                  SharedPreferences.Editor ed = prefs.edit();
                  ed.putBoolean("value", true);
                  ed.apply();
                } else {
                  parentView.setImageResource(R.drawable.white);
                  SharedPreferences.Editor ed = prefs.edit();
                  ed.putBoolean("value", false);
                  ed.apply();
                }
        }
    }
}