android - onPageSelected 不适用于第一页

Question

我的寻呼机适配器(扩展 PagerAdepter)中有一个 TextView 。我用 MainActivity 的 onPageSelected 更新了这个 TextView 。其位置 > 0 的更新 TextView ，但启动页面(位置 0)不会在启动时更新。当我向前滑动然后向后滑动；它为位置 0 设置值，但我无法在开始时设置值。星页如何设置值？

public void onPageSelected(int position) {

             switch (position) {
                case 0: 

                     PagerAdapter.tv.setText("value"); // => doesnt work on start

                    break;

                            default:
                                   PagerAdapter.tv.setText("value");
                                         break;
}
}

完整代码:

public class QuizStart extends SlidingFragmentActivity {
 @Override
        protected void onCreate(final Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

           this.setContentView(R.layout.activity_main);

              mPager = (ViewPager)findViewById(R.id.pager);         
            QuestionPagerAdapter mAdapter = new QuestionPagerAdapter();

            mPager.setAdapter(mAdapter);
            QuizStart.onPageSelected(0);

         mPager.setOnPageChangeListener(new OnPageChangeListener() {


            @Override
            public void onPageScrollStateChanged(int arg0) { }

            @Override
            public void onPageScrolled(int arg0, float arg1, int arg2) { }

            @Override
            public void onPageSelected(int position) {

             switch (position) {
                case 0: 

                     PagerAdapter.tv.setText("value"); // => doesnt work on start

                    break;

                            default:
                                   PagerAdapter.tv.setText("value");
                                         break;
                }
            }

        });
}
}

Answer 1

您可以在创建 OnPageChangeListener 时手动调用 onPageSelected(0) 来设置起始状态:

OnPageChangeListener pageChangeListener = new OnPageChangeListener() {
    @Override
    public void onPageScrollStateChanged(int arg0) { }

    @Override
    public void onPageScrolled(int arg0, float arg1, int arg2) { }

    @Override
    public void onPageSelected(int position) {

        switch (position) {
        case 0: 
            QuizStart.next.setText(getmycurrentpage()+"");
            break;

        default:

            QuizStart.next.setText(getmycurrentpage()+"");
            break;
        }
    }
});

   mPager.setOnPageChangeListener(pageChangeListener);
   // do this in a runnable to make sure the viewPager's views are already instantiated before triggering the onPageSelected call
   mPager.post(new Runnable()
   {
       @Override
       public void run() 
       {
           pageChangeListener .onPageSelected(viewPager.getCurrentItem());
       }
   });

编辑

现在它不会得到 @metemet06

所指出的 Null Pointer exception