Android开发：如何计算TimePicker选中时间与当前时间的差值

Hey there! Let's get that time difference calculation working for you. First, a quick note: your original code grabs the current time only when the activity starts, which will be outdated if the user waits to select a time. We'll fix that and add the difference logic step by step.

Here's the revised code with full time difference functionality:

public class ScheduleMessage extends AppCompatActivity {
    TextView textView;
    TimePicker timePicker;
    String date, timeDifference;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_schedule_message);
        
        timePicker = findViewById(R.id.simpleTimePicker);
        textView = findViewById(R.id.selectedTime);
        
        timePicker.setOnTimeChangedListener(
                new TimePicker.OnTimeChangedListener() {
                    @Override
                    public void onTimeChanged(TimePicker view, int hourOfDay, int minute) {
                        // 1. Get fresh current time when the user selects a time
                        Calendar currentCalendar = Calendar.getInstance();
                        long currentTimeMillis = currentCalendar.getTimeInMillis();
                        
                        // 2. Create a Calendar for the selected time (same date as current)
                        Calendar selectedCalendar = Calendar.getInstance();
                        selectedCalendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                        selectedCalendar.set(Calendar.MINUTE, minute);
                        selectedCalendar.set(Calendar.SECOND, 0); // Standardize seconds to 0
                        selectedCalendar.set(Calendar.MILLISECOND, 0);
                        long selectedTimeMillis = selectedCalendar.getTimeInMillis();
                        
                        // 3. Calculate the raw difference in milliseconds
                        long differenceMillis = selectedTimeMillis - currentTimeMillis;
                        
                        // 4. Convert milliseconds to hours and minutes for readability
                        long hours = differenceMillis / (1000 * 60 * 60);
                        long minutes = (differenceMillis % (1000 * 60 * 60)) / (1000 * 60);
                        
                        // Format the selected time string
                        date = String.format("%02d:%02d", hourOfDay, minute);
                        // Handle negative differences (selected time is earlier in the day)
                        timeDifference = String.format("%s%02d hours %02d minutes", 
                                differenceMillis < 0 ? "-" : "", 
                                Math.abs(hours), 
                                Math.abs(minutes));
                        
                        // Update the TextView with all details
                        textView.setText(String.format("Selected: %s | Current: %s | Difference: %s",
                                date,
                                new SimpleDateFormat("HH:mm").format(currentCalendar.getTime()),
                                timeDifference));
                    }
                });
    }
}

Key Details: #

• Up-to-date current time: We fetch the current time inside the onTimeChanged method, so it always reflects the exact moment the user selects a time.
• Calendar-based calculation: Using Calendar objects lets us easily convert times to millisecond timestamps, which simplifies calculating the difference.
• Readable output: We convert the raw millisecond difference into hours and minutes, and handle negative values (when the selected time is earlier in the day than the current time) by adding a minus sign.
• Clean formatting: String.format ensures times are displayed with leading zeros (e.g., 09:05 instead of 9:5) for consistency.

内容的提问来源于stack exchange，提问作者HARSH ASHRA