How to prevent multiple instances of app/activity when it is started from Intent.createChooser()?

Question

I have a simple app with a single TextView which displays plain text from an ACTION_SEND intent. My issue is that every time that some text is shared to this app a new instance is created. I can see multiple instances of the app on checking the recent apps. I'm testing it on API 23.

This is my code:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d("MainActivity.java", "onCreate");

        ((TextView) findViewById(R.id.temp_textview)).setText("Share text/links from other apps");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Intent intent = getIntent();
        String action = intent.getAction();
        intent.getFlags();
        Log.d("onResume - intent: ",intent.toString());
        String type = intent.getType();
        TextView displayText = (TextView) findViewById(R.id.temp_textview);

        if (Intent.ACTION_SEND.equals(action) && type!=null) {
            Log.d("MainActivity.java", "Intent verified");
            if ("text/plain".equals(type)) {
                handleSendText(intent, displayText);
            }
        }
    }

    void handleSendText(Intent intent, TextView displayText) {
        String sharedText = intent.getStringExtra(Intent.EXTRA_TEXT);
        Log.d("MainActivity.java", sharedText);
        if (sharedText != null) {
            displayText.setText(sharedText);
        }
    }
}

I have tried fiddling with the launchMode in the manifest but none of the options solved the issue.

Edit 1:

Here's my manifest file:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="chaitanya.im.example">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
            <intent-filter>
                <action android:name="android.intent.action.SEND" />
                <category android:name="android.intent.category.DEFAULT" />
                <data android:mimeType="text/plain" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Answer 1

Normally, if another application launches your Activity (via ACTION_SEND, for example), your Activity will be launched into the existing task of the other app. So if you use 5 other apps and each of them launch your Activity using ACTION_SEND, you will have 5 instances of your Activity, each in a separate task.

If you want your Activity to run by itself, in its own task, and not in the other app's task, then you need to specify launchMode="singleTask" in the <activity> declaration in the manifest for this Activity. Then, when another app launches your Activity, the Activity will be launched in a separate task. If there is already an instance of the Activity running in that task, then Android will not create a new instance of the Activity, it will just call onNewIntent() and deliver the Intent that the other app used in the call to startActivity().