Question

public class TimePickerClass  extends Activity{

public TimePicker mTimePicker;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_time_picker_class);
Button saveTimeButton;
mTimePicker = (TimePicker) findViewById(R.id.timePicker);
mTimePicker.setIs24HourView(true);
saveTimeButton = (Button) findViewById(R.id.next_button);
saveTimeButton.setOnClickListener(v -> {
    getTime();
});

  public String getTime(){
//TODO
int hour;
int minute;
hour = mTimePicker.getHour();
minute = mTimePicker.getMinute();
String message;
message = "Time:" + hour +" : " + minute;
return message;
}

你好！我有一个类，其中使用TimePicker获取用户选择的时间。我正在尝试这样做：

TimePickerClass time = new TimePickerClass();
String userTime = time.getTime();

但是这不起作用，应用程序已关闭。那如何实现呢？错误如下：

FATAL EXCEPTION: main
          Process: com.gfc.glanceclock, PID: 32256
          java.lang.NullPointerException: Attempt to invoke virtual method 'int android.widget.TimePicker.getHour()' on a null object reference

Answer 1

您正在尝试自己创建活动，这就是为什么未调用必要的生命周期方法而您获得NullPointerException的原因。

如果您想从TimePickerClass活动中获取时间，请启动它以获取结果，例如：

Intent intent = new Intent(context, TimePickerClass.class)
startActivityForResult(intent, REQUEST_CODE)

以及您的TimePickerClass活动中的设置结果：

mTimePicker.setOnTimeChangedListener(new TimePicker.OnTimeChangedListener() {

            public void onTimeChanged(TimePicker view, int hourOfDay, int minute) {
                 Intent intent = new Intent();
                 intent.putExtra("time", time.getTime());
                 setResult(RESULT_OK, intent);
                 finish();
            }
        });

然后您可以处理结果

protected void onActivityResult(int requestCode, int resultCode, Intent data)

方法。

您可以详细了解here。

Answer 2

您需要使用setOnTimeChangedListener()来实现此目的：-

当您尝试使用button click事件调用计时器方法时，计时器将获得NullPointerException。

mTimePicker.setOnTimeChangedListener(new TimePicker.OnTimeChangedListener() {

            public void onTimeChanged(TimePicker view, int hourOfDay, int minute) {
                 getTime();
            }
        });

如何在另一个课程中从timePicker获取时间？

2 个答案: