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

我试图在我的Android设备上运行我的Android应用程序，但它一直显示我的主活动不存在，尽管我的主活动类在那里

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.

我试图创建一个新的项目，然后复制我以前的代码，它在一段时间内奏效了。但随后它又产生了同样的错误。

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:

在5月份的Android清单中已经有了一个意图过滤器：

        <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.

我已经试着清理和重建项目了。但它仍然得到相同的错误。我的安卓设备版本是安卓9。

Here is my main activity:

以下是我的主要活动：

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);
        }


    }
}

优秀答案推荐

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

你可以尝试使用以下ADB命令卸载应用程序并重新运行吗？

adb uninstall <your-apps-package-name>

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

您可以删除IDEA文件夹，然后重新启动您的项目。

I have had this happen to me once when I enabled the Fingerprint / PIN lock on the AVD and ran the app afterwards.

我有一次遇到过这种情况，当时我启用了AVD上的指纹/PIN锁，然后运行了这款应用程序。

I found I needed to unlock the device before running the app.

我发现我需要在运行这款应用程序之前解锁设备。

Take the path:

走这条路：

tab Run / edit Configuration / tab general / Lunch Options / launch.

选项卡运行/编辑配置/选项卡常规/午餐选项/启动。

And select the default activity option.
If the problem does not resolve, select the Specified Activity option and select the MainActivity.

并选择默认活动选项。如果问题没有解决，请选择指定的活动选项，然后选择MainActivity。

If the problem is resolved, it is likely that the activity path is in the wrong androidManifest. You can write the path completely in androidmanifest.

如果问题得到解决，很可能是活动路径位于错误的androidManifest中。您可以将路径完整地写在android清单中。

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

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

In the code above write the path of the activity instead of the word path.
And also go back app configurations and choose the default activity one again.

在上面的代码中，写下活动的路径，而不是单词路径。还可以返回应用程序配置，再次选择默认活动。

Had this in react native, all the above solutions did not work for me
while in root, I did cd android
then ./gradlew uninstallAll
then after its done, cd out , run the project and the error was gone

在REACT本机中，以上所有解决方案都不适用于我在根目录下，然后我做了CD Android。/gradlew卸载完成后，CD出来，运行项目，错误消失了

Add the intent-filter to the AndroidManifest.xml:

将Intent-Filter添加到androidManifest.xml：

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

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

try this

尝尝这个

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

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

or

或

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

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

or

或

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

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

You can look at this response here Error type 3 Error: Activity class {} does not exist.

您可以在此处查看此响应错误类型3错误：活动类{}不存在。

Also, another common problem is if you are running your app on a physical device that has multiple user accounts. E.g. Main User and A Guest User. In this case there might be a conflict if one user does not update their application. Follow the following steps;

此外，另一个常见的问题是，如果你在有多个用户账户的物理设备上运行应用程序。例如，主用户和访客用户。在这种情况下，如果一个用户不更新其应用程序，则可能会发生冲突。遵循以下步骤；

1. Go to Settings.


2. Go to Apps.


3. Select your app.


4. Open the overflow menu on the top right and select Uninstall for all users.


5. Done. Try to install then launch your app again.

The other alternative, which is longer, is to uninstall the app while in one account, then switch accounts and uninstall in the other.

另一种更长的选择是，在一个账户中卸载应用程序，然后在另一个账户中切换账户并卸载。

Hope it helps.

希望能有所帮助。

The same error occurred to me and I solved it by renaming the package and using "clean project and rebuild project" ... then I shut down android stodio and restarted it then it worked fine.

同样的错误也发生在我身上，我通过重命名包并使用“清理项目和重建项目”来解决它。然后，我关闭了安卓系统，然后重启了它，然后它运行得很好。

You can look at this response here Error type 3 Error: Activity class {} does not exist.

您可以在此处查看此响应错误类型3错误：活动类{}不存在。

Also, another common problem is if you are running your app on a physical device that has multiple user accounts. E.g. Main User and A Guest User. In this case there might be a conflict if one user does not update their application. Follow the following steps;

此外，另一个常见的问题是，如果你在有多个用户账户的物理设备上运行应用程序。例如，主用户和访客用户。在这种情况下，如果一个用户不更新其应用程序，则可能会发生冲突。遵循以下步骤；

Go to Settings.
Go to Apps.
Select your app.
Open the overflow menu on the top right and select Uninstall for all users.
Done. Try to install then launch your app again.
The other alternative, which is longer, is to uninstall the app while in one account, then switch accounts and uninstall in the other.

转到设置。转到应用程序。选择您的应用程序。打开右上角的溢出菜单，然后选择为所有用户卸载。好了。尝试安装，然后再次启动您的应用程序。另一种更长的选择是，在一个账户中卸载应用程序，然后在另一个账户中切换账户并卸载。