android - How to remove all Activities except root activity with launch mode and activity alias?

Question

I'm studying launch mode intent flag and activity alias in Android programming.

There are activities (A - B - A - B) in back stack, and I want to start activity A and I also want to reuse A at bottom of back stack. So final state of back stack I want is just (A).

To do so, I write code like this

A (MainActivity)

package com.example.intentflagexampele;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

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

        findViewById(R.id.button).setOnClickListener(v -> {
            Intent intent = new Intent(MainActivity.this, MainActivity2.class);
            startActivity(intent);
        });
    }
}

B (MainActivity2)

package com.example.intentflagexampele;

import androidx.appcompat.app.AppCompatActivity;

import android.content.ComponentName;
import android.content.Intent;
import android.os.Bundle;

public class MainActivity2 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        findViewById(R.id.button).setOnClickListener(v -> {
            Intent intent = new Intent(MainActivity2.this, MainActivity.class);
            startActivity(intent);
        });

        findViewById(R.id.button2).setOnClickListener(v -> {
            Intent intent = new Intent();
            ComponentName componentName = new ComponentName(MainActivity2.this,
                    "com.example.intentflagexampele.SplashActivity");
            intent.setComponent(componentName);
            intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP | Intent.FLAG_ACTIVITY_CLEAR_TOP);
            startActivity(intent);
        });
    }
}

AndroidManifest.xml

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.IntentFlagExample2">
        <activity android:name=".MainActivity2"/>
        <activity android:name=".MainActivity">
        </activity>

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

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

</manifest>

The problem is that whenever I start SplashActivity with button2, Back Stack become (A - B - A) not (A).

What should I do? Is there something wrong?

question from:https://stackoverflow.com/questions/65949043/how-to-remove-all-activities-except-root-activity-with-launch-mode-and-activity

Answer 1

Try something like this:

Intent intent = new Intent(this, A.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_NEW_TASK); 
startActivity(intent);

This will clear the back stack of activities.