Hey there! I’ve run into this exact problem when building an SMS-focused app, so let me break down the solution step by step—this should get you up and running with SIM selection before sending texts.

First, Understand the API Background #

Before Android 5.1 (API Level 22), there was no official support for dual-SIM SMS control. So if your app targets devices below this version, you’ll have to inform users that SIM selection isn’t available. For API 22+, Google introduced the SubscriptionManager class to handle multi-SIM operations, which is what we’ll rely on here.

Step 1: Request Necessary Permissions #

You’ll need these permissions in your AndroidManifest.xml:

<uses-permission android:name="android.permission.SEND_SMS" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />
<!-- For Android 10+, use READ_PHONE_NUMBERS instead of READ_PHONE_STATE -->
<uses-permission android:name="android.permission.READ_PHONE_NUMBERS" android:maxSdkVersion="29" />

Don’t forget to request these permissions at runtime, especially for Android 6.0 (API 23) and above—users need to explicitly grant access to phone state and SMS features.

Step 2: Fetch Available Active SIM Cards #

Use SubscriptionManager to get a list of active SIMs with their details (like carrier name, phone number, and unique subscription ID). Here’s a code snippet:

private List<SubscriptionInfo> getActiveSIMs() {
    SubscriptionManager subscriptionManager = getSystemService(SubscriptionManager.class);
    List<SubscriptionInfo> activeSubscriptions = new ArrayList<>();
    
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_PHONE_STATE) == PackageManager.PERMISSION_GRANTED) {
        activeSubscriptions = subscriptionManager.getActiveSubscriptionInfoList();
    }
    return activeSubscriptions;
}

This will give you a list of SubscriptionInfo objects—each represents an active, usable SIM card in the device.

Step 3: Show a SIM Selection Dialog #

Once you have the list, create an alert dialog to let users pick their preferred SIM. Here’s how to build it:

private void showSIMSelectionDialog(List<SubscriptionInfo> simList) {
    if (simList.isEmpty()) {
        Toast.makeText(this, "No active SIM cards found", Toast.LENGTH_SHORT).show();
        return;
    }
    if (simList.size() == 1) {
        // Only one SIM available—send directly without selection
        sendSMSWithSIM(simList.get(0).getSubscriptionId());
        return;
    }

    String[] simOptions = new String[simList.size()];
    for (int i = 0; i < simList.size(); i++) {
        SubscriptionInfo sim = simList.get(i);
        simOptions[i] = sim.getCarrierName() + " (" + sim.getNumber() + ")";
    }

    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setTitle("Choose SIM to Send SMS")
           .setItems(simOptions, (dialog, which) -> {
               int selectedSubId = simList.get(which).getSubscriptionId();
               sendSMSWithSIM(selectedSubId);
           })
           .show();
}

This dialog displays each SIM’s carrier name and associated phone number for clear, user-friendly selection.

Step 4: Send SMS Using the Selected SIM #

Use SMSManager.getSMSManagerForSubscriptionId() to get an instance tied to the user’s chosen SIM, then send your message:

private void sendSMSWithSIM(int subId) {
    String recipientNumber = "RECIPIENT_PHONE_NUMBER"; // Replace with actual number
    String smsContent = "Your message content here";
    
    try {
        SMSManager smsManager = SMSManager.getSMSManagerForSubscriptionId(subId);
        smsManager.sendTextMessage(recipientNumber, null, smsContent, null, null);
        Toast.makeText(this, "SMS sent successfully", Toast.LENGTH_SHORT).show();
    } catch (Exception e) {
        Toast.makeText(this, "Failed to send SMS: " + e.getMessage(), Toast.LENGTH_SHORT).show();
        e.printStackTrace();
    }
}

Key Notes & Edge Cases #

• Permissions Check: Always verify you have the required permissions before accessing SubscriptionManager—otherwise, you’ll hit a SecurityException.
• API Compatibility: For devices below API 22, you can’t specify a SIM—fall back to the system default, or show a message telling users SIM selection isn’t supported on their device.
• Carrier Restrictions: Some carriers may block SMS from certain SIMs (e.g., data-only SIMs), so make sure to handle exceptions gracefully.

Putting it all together: When the user triggers an SMS send, call getActiveSIMs(), then pass the result to showSIMSelectionDialog() to let them pick their SIM before sending.

内容的提问来源于stack exchange，提问作者Samrat Lahiri