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直接給代碼*-*

Fragment：

public boolean onKeyDown(int keyCode, KeyEvent event){if ((keyCode == KeyEvent.KEYCODE_BACK)){//執行操作((MainActivity) Objects.requireNonNull(getActivity())).viewPager.setCurrentItem(3); }return true;}

MainActivity：

@BindView(R.id.viewPager)public ViewPager viewPager;Fragment currentFragment; viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener(){@Overridepublic void onPageScrolled(int position, float positionOffset, int positionOffsetPixels){}@Overridepublic void onPageSelected(int position){FragmentManager fragmentManager = MainActivity.this.getSupportFragmentManager();List<Fragment> fragments = fragmentManager.getFragments();currentFragment=fragments.get(position);……}@Overridepublic void onPageScrollStateChanged(int state){}});setupViewPager(viewPager); private void setupViewPager(ViewPager viewPager){adapter = new ViewFragmentPagerAdapter(getSupportFragmentManager());adapter.addFragment(MainFragment.newInstance(getResources().getString(R.string.app_title)));adapter.addFragment(new Fragment());……viewPager.setAdapter(adapter);viewPager.setOffscreenPageLimit(5);} // 用來計算返回鍵的點擊間隔時間private long exitTime = 0;@Overridepublic boolean onKeyDown(int keyCode, KeyEvent event){if(currentFragment!=null&&currentFragment instanceof AboutApp){((AboutApp)currentFragment).onKeyDown(keyCode, event);return true;} else if (isTaskRoot()){if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN){if ((System.currentTimeMillis() - exitTime) > 2000){Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();exitTime = System.currentTimeMillis();}else{finish();}return true;}}return super.onKeyDown(keyCode, event);}

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總結

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