正在开发一个 Android 应用程序，其中每个 Activity 都有自己的计时器。最初我在每个类
中都有这样的代码public void tTimer() {
mTextField = (TextView) findViewById(R.id.countDown_timer);
final CountDownTimer tCounter = new CountDownTimer(7000, 1000) {
@Override
public void onTick(long millisUntilFinished) {
mTextField
.setText("Time Remaining: "
+ String.format(
"%d min, %d sec",
TimeUnit.MILLISECONDS
.toMinutes(millisUntilFinished),
TimeUnit.MILLISECONDS
.toSeconds(millisUntilFinished)
- TimeUnit.MINUTES
.toSeconds(TimeUnit.MILLISECONDS
.toMinutes(millisUntilFinished))));
}
@Override
public void onFinish() {
mTextField.setText("Done!");
Intent i = new Intent (ColdActivity.this, PopUpActivity.class);
startActivity(i);
}
};
Button startButton = (Button) findViewById(R.id.timer_button_start);
/* When the Start Button is touched, the Countdown Timer will start */
startButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog.Builder builder = new AlertDialog.Builder(
ColdActivity.this);
builder.setNegativeButton("Dismiss",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface arg0, int arg1) {
tCounter.start();
// Once the user has been notified that they should increase
// their alarm volume, and they dismiss the notification, the timer
// will start
}
});
builder.setTitle("Notification");
builder.setMessage("It is recommended that you turn your Alarm/Ringtone volume on so that you can hear the alarm when it is finished");
AlertDialog dlg = builder.create();
dlg.show();
}
});
Button stopButton = (Button) findViewById(R.id.timer_button_cancel);
/* When the Stop Button is touched, the Countdown Timer will stop */
stopButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
tCounter.cancel();
}
});
}
我现在尝试创建一个新类，它有一个名为 tTimer() 的方法，如上面的代码所示，以便我可以实例化该类的新对象，然后调用该方法在 onCreate() 中，这样我就不必像以前那样在每个类中重写计时器代码。
我尝试像这样参数化该方法:
CustomTimerActivity cGT = new CustomTimerActivity();
cGT.tTimer(7000, ColdActivity.this, R.id.countDown_timer, R.id.timer_button_start, R.id.timer_button_cancel);
我不断得到的是 NullPointerException，它指向我的名为 CustomTimerActivity
为什么我无法将资源 ID 作为参数传递？还是 NPE 来自其他地方？
这是我制作的CustomTimerActivity:
public class CustomTimerActivity extends Activity {
TextView mTextField;
int mId;
public void tTimer(long millisecs, final Activity activity1, int tv, int start, int cancel) {
mTextField = (TextView) findViewById(tv);
final CountDownTimer tCounter = new CountDownTimer(millisecs, 1000) {
@Override
public void onTick(long millisUntilFinished) {
mTextField
.setText("Time Remaining: "
+ String.format(
"%d min, %d sec",
TimeUnit.MILLISECONDS
.toMinutes(millisUntilFinished),
TimeUnit.MILLISECONDS
.toSeconds(millisUntilFinished)
- TimeUnit.MINUTES
.toSeconds(TimeUnit.MILLISECONDS
.toMinutes(millisUntilFinished))));
}
@Override
public void onFinish() {
mTextField.setText("Done!");
Intent i = new Intent (activity1, PopUpActivity.class);
startActivity(i);
}
};
Button startButton = (Button) findViewById(start);
/* When the Start Button is touched, the Countdown Timer will start */
startButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog.Builder builder = new AlertDialog.Builder(
activity1);
builder.setNegativeButton("Dismiss",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface arg0, int arg1) {
tCounter.start();
// Once the user has been notified that they should increase
// their alarm volume, and they dismiss the notification, the timer
// will start
}
});
builder.setTitle("Notification");
builder.setMessage("It is recommended that you turn your Alarm/Ringtone volume on so that you can hear the alarm when your tea is finished");
AlertDialog dlg = builder.create();
dlg.show();
}
});
Button stopButton = (Button) findViewById(cancel);
/* When the Stop Button is touched, the Countdown Timer will stop */
stopButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
tCounter.cancel();
}
});
}
}
问题一定与 findViewById() 和用作输入的 Id 有关，对吧？
这是调用 Intent 时遇到的另一个 NullPointerException。
最佳答案
该 Activity 尚未在构造函数中初始化。仅在构造函数中收集参数并在 onCreate(Bundle) 方法中进行初始化!
但是，如果您想从 givin Activity 中调用它，则必须在该类上调用 .findViewById，而不是在您自己的类上调用 .findViewById
关于java - 如何将资源 ID 作为参数传递；没有空指针异常，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28903948/