Android：比较当前时间与TimePicker输入时间时单数字时间匹配异常

Hey Rajat, I see exactly where the problem is—your substring-based time parsing is failing for single-digit hours or minutes because it relies on fixed character positions, which don't hold when the time has only one digit for hour/minute. Let's break this down and fix it step by step.

The Root Cause #

When you use substring to slice the time string (like grabbing the first 2 characters for hour), it works fine for times like 10:10 (since the hour is two digits). But for 1:10, the first two characters are 1:, which isn't a valid hour number. This throws off your conditional logic, sending it into the ELSE branch instead of the intended one for single-digit times.

Solution: Use Dynamic Time Splitting Instead of Fixed Substrings #

Instead of relying on fixed character indices, split the time string by the colon (:) to separate hours and minutes. This works reliably for both single-digit and double-digit time values.

Step 1: Split the User-Input Time #

First, take the time from your TimePicker and split it into hour and minute components:

String targetTime = yourTimePicker.getText().toString();
String[] timeComponents = targetTime.split(":");

// Parse to integers (handle potential invalid input with try-catch)
int targetHour = 0;
int targetMinute = 0;
try {
    targetHour = Integer.parseInt(timeComponents[0]);
    targetMinute = Integer.parseInt(timeComponents[1]);
} catch (NumberFormatException | ArrayIndexOutOfBoundsException e) {
    // Handle invalid time format (e.g., show error to user)
    e.printStackTrace();
}

Step 2: Get Current Time Values #

Retrieve the current hour and minute using a reliable time API (choose based on your Android API level):

// For API level <26, use Calendar
Calendar currentTime = Calendar.getInstance();
int currentHour = currentTime.get(Calendar.HOUR_OF_DAY); // Use HOUR for 12-hour format
int currentMinute = currentTime.get(Calendar.MINUTE);

// For API level >=26, use LocalDateTime (cleaner)
// LocalDateTime now = LocalDateTime.now();
// int currentHour = now.getHour();
// int currentMinute = now.getMinute();

Step 3: Compare Times & Trigger Vibration #

Now compare the integer values directly—no more string-based branch confusion:

@Override
public void onTick(long millisUntilFinished) {
    // Refresh current time each tick
    Calendar currentTime = Calendar.getInstance();
    int currentHour = currentTime.get(Calendar.HOUR_OF_DAY);
    int currentMinute = currentTime.get(Calendar.MINUTE);

    if (currentHour == targetHour && currentMinute == targetMinute) {
        // Trigger vibration
        Vibrator vibrator = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
        if (vibrator != null && vibrator.hasVibrator()) {
            vibrator.vibrate(1000); // Vibrate for 1 second—adjust as needed
        }
        // Optional: Cancel the timer if you don't want repeated vibrations
        // yourCountDownTimer.cancel();
    }
}

Why This Works #

By splitting the time string dynamically, you avoid the pitfalls of fixed-position substring calls. Whether the user enters 1:10 or 12:34, split(":") will always give you the correct hour and minute as separate elements, which you can safely convert to integers for comparison.

Bonus: Avoid Invalid Inputs #

Adding a try-catch block around the integer parsing ensures your app doesn't crash if the user enters a malformed time (like 10-10 instead of 10:10). You can also add input validation to the TimePicker to enforce the correct HH:mm or H:mm format upfront.

内容的提问来源于stack exchange，提问作者Rajat