[英]Hide item in ActionBar in Activity with Fragments in ViewPager
要求 -我有一個應用程序,其中有3個片段封裝在ViewPager中。 活動中有一個工具欄,其中有2個菜單項,我只想在選擇第二個片段時才顯示其中一個。
問題 -我的代碼拋出NullPointerException
堆棧跟蹤:
11-27 15:10:01.940 25899-25899/com.example.michael.ims_application_apps E/AndroidRuntime: java.lang.NullPointerException
11-27 15:10:01.940 25899-25899/com.example.michael.ims_application_apps E/AndroidRuntime: at com.example.michael.ims_application_apps.MainActivity.onCreateOptionsMenu(MainActivity.java:67)
11-27 15:10:01.940 25899-25899/com.example.michael.ims_application_apps E/AndroidRuntime: at android.app.Activity.onCreatePanelMenu(Activity.java:2476)
11-27 15:10:01.940 25899-25899/com.example.michael.ims_application_apps E/AndroidRuntime: at android.support.v4.app.FragmentActivity.onCreatePanelMenu(FragmentActivity.java:262)
11-27 15:10:01.940 25899-25899/com.example.michael.ims_application_apps E/AndroidRuntime: at android.support.v7.internal.view.WindowCallbackWrapper.onCreatePanelMenu(WindowCallbackWrapper.java:85)
11-27 15:10:01.
這是我的活動
public class MainActivity extends AppCompatActivity
{
private ViewPager pager;
private AdapterFragment mAdapter;
private PageIndicator mIndicator;
private String name;
MyTimer tim;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
android.support.v7.widget.Toolbar myToolbar = (android.support.v7.widget.Toolbar) findViewById(R.id.tool_bar);
setSupportActionBar(myToolbar);
getSupportActionBar().setDisplayShowHomeEnabled(true);
getSupportActionBar().setIcon(R.mipmap.ic_launcher);
// Pada activity ini akan make AdapterFragment
mAdapter = new AdapterFragment(getSupportFragmentManager());
// Untuk ViewPagerIndicator
pager = (ViewPager)findViewById(R.id.pager);
pager.setAdapter(mAdapter);
// TitlePageIndicator merupakan class di library ViewPagerIndicator
mIndicator = (TitlePageIndicator)findViewById(R.id.indicator);
mIndicator.setViewPager(pager);
if(pager.getCurrentItem() != 1)
{
MenuItem sync = (MenuItem) findViewById(R.id.action_sync);
sync.setVisible(false);
}
//Hidupin session waktu N.B: Waktu boleh berapa lama apps ke-pause secara pastinya belum diset !!!!
// tim = new MyTimer(50000,10);
}
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item)
{
int id = item.getItemId();
// set OptionButton yang di device
switch (id)
{
case R.id.action_sync:
if(pager.getCurrentItem() != 1)
{
Log.d("Tag", pager.getCurrentItem()+"");
setVisible(false);
}
Toast.makeText(this, "Sync", Toast.LENGTH_LONG).show();
return true;
case R.id.Logout:
SharedPreferences setting = getSharedPreferences("USER", 0);
SharedPreferences.Editor editor = setting.edit();
editor.putString("userName", "-1");
editor.commit();
Intent i = new Intent(MainActivity.this, LoginActivity.class);
startActivity(i);
finish();
}
return super.onOptionsItemSelected(item);
}
誰能幫助我解決問題? 謝謝
覆蓋活動的onPrepareOptionsMenu(Menu menu)
,然后在其中放置隱藏/顯示邏輯。
public boolean onPrepareOptionsMenu(Menu menu) {
MenuItem item = menu.findItem(R.id.action_sync);
item.setVisible(pager.getCurrentItem() == 1);
return true;
}
然后,每當出現不同的片段時,調用活動的invalidateOptionsMenu()
( 請參閱ViewPager.OnPageChangeListener )。 它將觸發onPrepareOptionsMenu(Menu menu)
。
viewPager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
invalidateOptionsMenu();
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
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