Question

这是我的代码

public class GameStartActivity extends AppCompatActivity {

TextView timerTV;
Timer20 timer;
@Override
protected void onCreate(Bundle savedInstanceState) {
    timerTV = (TextView) findViewById(R.id.timerTV);
    timer = new Timer20(20000, 1000);
    timer.start();

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_game_start);
}

public class Timer20 extends CountDownTimer {

    public Timer20(long startTime, long interval) {
        super(startTime, interval);
    }

    @Override
    public void onFinish() {
        start();
    }

    @Override
    public void onTick(long millisUntilFinished) {
        timerTV.setText( "0:" + String.valueOf( millisUntilFinished / 1000 ) );
    }

}
}

我在timerTV.setText ......行上得到了这个错误。：

java.lang.NullPointerException：尝试在空对象引用上调用虚方法'void android.widget.TextView.setText（java.lang.CharSequence）'

因此，当我达到这个意图时，它会因此崩溃。

Answer 1

您需要在setContentView

中的onCreate后初始化您的观看次数

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_game_start);

    timerTV = (TextView) findViewById(R.id.timerTV);
    timer = new Timer20(20000, 1000);
    timer.start();
}

Answer 2

您应该在开头本身初始化onCreate中的视图。

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_game_start);
timerTV = (TextView) findViewById(R.id.timerTV);
timer = new Timer20(20000, 1000);
timer.start();
}

Android：TextView表现得像是null

2 个答案: