On Android, How to Switch Activities Programmatically

On Android, how do you switch activities programmatically?

This should do it for you:

Intent myIntent = new Intent(this, MyActivityName.class);
startActivity(myIntent);

You can call that from anywhere in your current activity.

How to switch between Android apps programmatically

I finally figured out how to switch between apps
programatically (preserving their state). In each app, I used 'getTaskId()' to get its task id and saved it to a file on /sdcard/.

Then, in each app, on a button click, I call

void switchTask()
{
  int tid;
  ActivityManager am;
  am = (ActivityManager)Ctx.getSystemService( Context.ACTIVITY_SERVICE );
  tid = getPkgTaskId();  // read task id of *other* app from file
  am.moveTaskToFront( tid, 0, null );
}

Note: These need permissions:

READ_EXTERNAL_STORAGE
WRITE_EXTERNAL_STORAGE
REORDER_TASKS

How can I configure Launcher activity programmatically in android?

Long story short, you cannot change the Activity that is launched by default. Update: There is an alternative as described by CommonsWare in another answer.

However, there are reasonable work arounds. In your MainActivity you can check whether the user is logged in and immediately redirect them to the LoginActivity. That has the added benefit of automatically returning to the MainActivity after you have logged in.

Alternatively, you can always go first to the LoginActivity, and if the user is already logged in, send them to the MainActivity (rewrite the Intent history to remove the return to LoginActivity or set the noHistory flag in the manifest).

Android Switch between activities

Here you aren't ever switching to the next Activity, just changing the layout of the current Activity

 new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                setContentView(R.layout.selectscreen); //where <next> is you target      activity :)
                }
            }, 5000);

instead of setContentView() you need to use an Intent

Intent i = new Intent(MainActivity.this, SelectPetsScreen.this);
startActivity(i);

Since you aren't actually going to the next Activity (java file) your onClick() isn't set.

Edit

This is what you are doing

public class MainActivity extends Activity {
Button fButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //Delay Code after 5 seconds
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            setContentView(R.layout.selectscreen); //where <next> is you target      activity :)
            }
        }, 5000);   
}

This is what you should be doing. Notice the difference in the run() function

public class MainActivity extends Activity {
Button fButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //Delay Code after 5 seconds
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            Intent i = new Intent(MainActivity.this, SelectPetsScreen.this);
            startActivity(i);
            }
        }, 5000);   
}

How to change main activity in Android programmatically

check this one below

Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
intent.setComponent(new ComponentName(packageName,mainActivity));
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
ctx.startActivity(intent);

Change Activity's theme programmatically

As docs say you have to call setTheme before any view output. It seems that super.onCreate() takes part in view processing.

So, to switch between themes dynamically you simply need to call setTheme before super.onCreate like this:

public void onCreate(Bundle savedInstanceState) {
    setTheme(android.R.style.Theme);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_second);
}

Change Activity in Android

There are tons of tutorials about this, also on Stackoverflow.
Reading the Docs would help too...
But here is the Solution you are searching for:
On Android, how do you switch activities programmatically?

Enable/disable an activity programmatically

Here's an example how to enable/disable an Activity:

    PackageManager pm = getPackageManager(); 
    pm.setComponentEnabledSetting(new ComponentName(this, com.packagename.MyActivity.class),
                                  PackageManager.COMPONENT_ENABLED_STATE_DISABLED, PackageManager.DONT_KILL_APP);

    pm.setComponentEnabledSetting(new ComponentName(this, com.packagename.MyActivity.class),
                                  PackageManager.COMPONENT_ENABLED_STATE_ENABLED, PackageManager.DONT_KILL_APP);