隱藏MenuItem按鈕並在ActionBar中顯示ProgressBar

我有一個包含片段的活動。在操作欄中有一個刷新按鈕，當按下時，我想要轉換爲進度條來顯示活動。雖然我收到以下錯誤：隱藏MenuItem按鈕並在ActionBar中顯示ProgressBar

Unable to start activity ComponentInfo{com.mycompany.myapp.Views.MasterDetails.MasterActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'android.view.MenuItem android.view.MenuItem.setActionView(android.view.View)' on a null object reference

在此行中：儘快itemBtnRefresh.setActionView(abprogress);爲背景的動作開始（「refreshData（）」）

上正確換一個按鈕，一個不確定的進度任何幫助嗎？

public class MasterActivity extends AppCompatActivity { 

    private String TAG = getClass().getSimpleName(); 

    private Toolbar mToolbar; 
    private ActionBar ab; 
    private MenuItem itemBtnRefresh; 
    private View abprogress; 

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

     mToolbar = (Toolbar) findViewById(R.id.masterToolBar); 
     setSupportActionBar(mToolbar); 
     ab = getSupportActionBar(); 
     ab.setDisplayHomeAsUpEnabled(true); 

     LayoutInflater inflater = (LayoutInflater) getApplicationContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     abprogress = inflater.inflate(R.layout.refresh_menuitem, null); 

     refreshData(); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     invalidateOptionsMenu(); 
     getMenuInflater().inflate(R.menu.menu_master, menu); 
     itemBtnRefresh = menu.findItem(R.id.master_refresh_action); 
     return super.onCreateOptionsMenu(menu); 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     switch (item.getItemId()) { 
      case R.id.master_refresh_action: 
       refreshData(); 
       return true; 
      default: 
       return super.onOptionsItemSelected(item); 
     } 
    } 

    public void refreshData() { 

     //... do a background task 
     // show the progressbar and hide the refresh button 

     itemBtnRefresh.setActionView(abprogress); 


     //.. finish the background task 
     // hide progressbar and show button 
     itemBtnRefresh.setActionView(null); 
    } 

}

menu_master.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android" 
     xmlns:app="http://schemas.android.com/apk/res-auto"> 
    <item 
     android:id="@+id/master_refresh_action" 
     android:icon="@drawable/ic_refresh" 
     android:title="Refresh" 
     app:showAsAction="ifRoom"/> 
</menu>

refresh_menuitem.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
       android:layout_width="wrap_content" 
       android:layout_height="wrap_content" 
       android:addStatesFromChildren="true" 
       android:focusable="true" 
       android:paddingLeft="4dp" 
       android:paddingRight="4dp" 
       android:gravity="center" 
       android:orientation="horizontal" 
       style="?attr/actionButtonStyle"> 
    <ProgressBar 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:focusable="true" 
     style="@android:style/Widget.Holo.ProgressBar.Small"/> 

</LinearLayout>

來源

2017-01-16 user-44651

onCreateOptionsMenu被onCreate，你的第一refreshData()電話後執行，所以'itemBtnRefresh'仍然是空。

嘗試在itemBtnRefresh之後立即調用onCreateOptionsMenu進行初始化。

來源

2017-01-16 15:59:32

隱藏MenuItem按鈕並在ActionBar中顯示ProgressBar

回答

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