OnClickListener引發NullPointerException

Question

我試圖將onClick偵聽器設置為ViewPager頁面中的按鈕，但是當我嘗試運行應用程序時，我得到了NullPointerException

....

public class MainActivity extends Activity {
    private ViewPager vPager;
    private MyPagerAdapter pagerAdapter;
    private TextView tv;
    private MyViewPagerListener pagerListener;
    private Button deleteAll;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tv=(TextView) findViewById(R.id.page_state);

        pagerListener = new MyViewPagerListener();
        pagerAdapter = new MyPagerAdapter();
        vPager = (ViewPager) findViewById(R.id.vPager);
        vPager.setAdapter(pagerAdapter);
        vPager.setCurrentItem(0);
        vPager.setOnPageChangeListener(pagerListener);
        //Here is the problem
        ClickListener cl = new ClickListener();
        deleteAll = (Button) vPager.findViewById(R.id.btnDelete);
        deleteAll.setOnClickListener(cl);
    }

    .....

}

Answer 1

您應該注冊一個新的OnClickListener對象，而不是ClickListener。 另外，您還必須提供onClick方法的實現，如下所示：

new OnClickListener() {
public void onClick(View v) {
  // do something when the button is clicked
}
};