braintree-android-drop-in: Crash in 'BrowserSwitchClient' in version 3.14.0

From: @TatyanaRTB

General information

• SDK/Library version: Android SDK 4.0.1
• Environment: Development
• Android Version and Device: All Android versions with various devices
• Braintree dependencies:

• com.braintreepayments.api:braintree:3.14.0
• com.braintreepayments.api:drop-in:4.6.0
• com.braintreepayments.api:google-payment:3.3.1

Issue description

The issue is related to https://github.com/braintree/braintree_android/issues/308. Firstly we observed crash from the #308 and now after fixes crash happens in next step by code, when BrowserSwitchOptions.start is called:

ThreeDSecure:

public static void continuePerformVerification(BraintreeFragment fragment, ThreeDSecureRequest request, ThreeDSecureLookup threeDSecureLookup) {
    boolean showChallenge = threeDSecureLookup.getAcsUrl() != null;
    String threeDSecureVersion = threeDSecureLookup.getThreeDSecureVersion();
    fragment.sendAnalyticsEvent(String.format("three-d-secure.verification-flow.challenge-presented.%b", showChallenge));
    fragment.sendAnalyticsEvent(String.format("three-d-secure.verification-flow.3ds-version.%s", threeDSecureVersion));
    if (!showChallenge) {
        completeVerificationFlowWithNoncePayload(fragment, threeDSecureLookup.getCardNonce());
    } else if (!threeDSecureVersion.startsWith("2.")) {
        fragment.browserSwitch(13487, ThreeDSecureV1BrowserSwitchHelper.getUrl(fragment.getReturnUrlScheme(), fragment.getConfiguration().getAssetsUrl(), request, threeDSecureLookup));
    } else {
        performCardinalAuthentication(fragment, threeDSecureLookup);
    }
}

BrowserSwitchFragment:

public void browserSwitch(int requestCode, String url) {
    BrowserSwitchOptions browserSwitchOptions = (new BrowserSwitchOptions()).requestCode(requestCode).url(Uri.parse(url));
    this.browserSwitchClient.start(browserSwitchOptions, this);
}

BrowserSwitchClient:

public void start(BrowserSwitchOptions browserSwitchOptions, Fragment fragment) {
    if (fragment instanceof BrowserSwitchListener) {
        this.start(browserSwitchOptions, fragment, (BrowserSwitchListener)fragment);
    } else {
        throw new IllegalArgumentException("Fragment must implement BrowserSwitchListener.");
    }
}

The issue can be reproduced by the following steps:

1. Select credit card option in DropIn dialog
2. Enter card parameters
3. Press Go/Next button on the keyboard two-three times: https://monosnap.com/file/kcCFXR7wLZkKU7MtGu1bgvD6dHJaqF

Please block the button from several payment attempts if request to Braintree API is already in progress. Several payment flows are started in parallel and BraintreeFragment is detached from Activity when receive first successful payment result. Other payment results cause this crash.

java.lang.IllegalStateException: Fragment must be attached to an activity.
	at com.braintreepayments.browserswitch.BrowserSwitchClient.start(BrowserSwitchClient.java:206) ~[na:0.0]
	at com.braintreepayments.browserswitch.BrowserSwitchClient.start(BrowserSwitchClient.java:186) ~[na:0.0]
	at com.braintreepayments.browserswitch.BrowserSwitchFragment.browserSwitch(BrowserSwitchFragment.java:59) ~[na:0.0]
	at com.braintreepayments.api.ThreeDSecure.continuePerformVerification(ThreeDSecure.java:266) ~[na:0.0]
	at com.braintreepayments.api.ThreeDSecure$3.onLookupComplete(ThreeDSecure.java:155) ~[na:0.0]
	at com.braintreepayments.api.ThreeDSecure$7.success(ThreeDSecure.java:503) ~[na:0.0]
	at com.braintreepayments.api.internal.HttpClient$3.run(HttpClient.java:288) ~[na:0.0]
	at android.os.Handler.handleCallback(Handler.java:739) ~[na:0.0]
	at android.os.Handler.dispatchMessage(Handler.java:95) ~[na:0.0]
	at android.os.Looper.loop(Looper.java:157) ~[na:0.0]
	at android.app.ActivityThread.main(ActivityThread.java:5429) ~[na:0.0]
	at java.lang.reflect.Method.invoke(Native Method) ~[na:0.0]
	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) ~[na:0.0]
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) ~[na:0.0]