Error: Activity class {.MainActivity} does not exist

Question

I tried to run my android application in my android device but it keeps saying that my Main Activity does not exist although my Main Activity class is there

I tried to create a new project then copied my previous codes and it worked for a while. But then it produced the same error again.

Error while executing: am start -n "com.example.sms/com.example.sms.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] cmp=com.example.sms/.MainActivity }
Error type 3
Error: Activity class {com.example.sms/com.example.sms.MainActivity} does not exist.

Error while Launching activity

There is already a intent-filter in may android manifest:

        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

I already tried to clean and rebuild project. But it still gets the same error. My android device's version is android 9.

Here is my main activity:

package com.example.sms;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Bundle;
import android.telephony.SmsManager;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    EditText etNumber, etMessage;
    Button btnSend;


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

        etNumber = (EditText)findViewById(R.id.etNumber);
        btnSend = (Button)findViewById(R.id.btnSend);
        btnSend.setOnClickListener(this);

    }

    public void MyMessage() {

        String phoneNum = etNumber.getText().toString().trim();
        String spamMessage = "Hi";

        if (etNumber.getText().toString().equals("09152006203")) {
            if (!etNumber.getText().toString().equals("")) {
                SmsManager smsManager = SmsManager.getDefault();
                ArrayList<String> sms = smsManager.divideMessage(spamMessage);
                smsManager.sendMultipartTextMessage(phoneNum, null,sms,null, null);

                Toast.makeText(this, "Message has been sent", Toast.LENGTH_SHORT).show();

            } else {
                Toast.makeText(this, "Please enter number or message", Toast.LENGTH_SHORT).show();
            }
        } else {
            Toast.makeText(this, "Number is incorrect!", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        switch(requestCode){

            case 0:
                if(grantResults.length>=0 && grantResults[0] == PackageManager.PERMISSION_GRANTED){
                    MyMessage();
                } else {
                    Toast.makeText(this, "You do not have required permission", Toast.LENGTH_SHORT).show();
                }
        }
    }

    @Override
    public void onClick(View v) {
        int permissionCheck = ContextCompat.checkSelfPermission(this, Manifest.permission.SEND_SMS);

        if(permissionCheck == PackageManager.PERMISSION_GRANTED){
            MyMessage();
        }
        else{
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.SEND_SMS}, 0);
        }


    }
}

Answer 1

Can you try uninstalling app using following ADB command and re-run?

adb uninstall <your-apps-package-name>

Answer 2

you can delete the folder of idea,then restart your project.