實現工具欄調用空對象引用

我有問題實施操作欄（我認爲現在被工具欄取代）。我想要的是一個有3個點的小下拉菜單，我可以有幾個選項，比如設置和點數。我試圖設置它，使菜單出現在homelistview.java頁面上。我覺得我一直在嘗試不同的解決方案，並且每次都會得到一個新的錯誤，並且總是指向下面提到的同一位置。實現工具欄調用空對象引用

setSupportActionBar(toolbar);

我原本以爲是因爲我沒有包含setContentView（R.layout.activity_main）;但其中包括2個內容視圖並不令人滿意。任何幫助，將不勝感激。

這是我的代碼。

styles.xml

<!-- Base application theme. --> 
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar"> 
    <!-- Customize your theme here. --> 
    <item name="colorPrimary">@color/colorPrimary</item> 
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item> 
    <item name="colorAccent">@color/colorAccent</item> 

</style> 

<style name="AppTheme.NoActionBar"> 
    <item name="windowActionBar">false</item> 
    <item name="windowNoTitle">true</item> 
</style> 

<style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" /> 

<style name="AppTheme.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />

--------------- menu_main.xml ------------- ------

<menu xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
tools:context="cs495capstone.edu.bsu.myapplication.MainActivity"> 
<item 
    android:id="@+id/action_settings" 
    android:orderInCategory="100" 
    android:title="@string/action_settings" 
    app:showAsAction="never" /> 
<item 
    android:id="@+id/action_credits" 
    android:orderInCategory="100" 
    android:title="@string/action_credits" 
    app:showAsAction="never" /> 
<item 
    android:id="@+id/action_lovely" 
    android:orderInCategory="100" 
    android:title="@string/action_lovely" 
    app:showAsAction="never" /> 
</menu>

-------------- activity_main.xml中----------------

<?xml version="1.0" encoding="utf-8"?> 
<android.support.design.widget.CoordinatorLayout 
xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:fitsSystemWindows="true" 
tools:context="cs495capstone.edu.bsu.myapplication.HomeActivityListview"> 

<android.support.design.widget.AppBarLayout 
    android:layout_height="wrap_content" 
    android:layout_width="match_parent" 
    android:theme="@style/AppTheme.AppBarOverlay"> 

    <android.support.v7.widget.Toolbar 
     android:id="@+id/toolbar" 
     android:layout_width="match_parent" 
     android:layout_height="?attr/actionBarSize" 
     android:background="?attr/colorPrimary" 
     app:popupTheme="@style/AppTheme.PopupOverlay" /> 

</android.support.design.widget.AppBarLayout> 

<include layout="@layout/activity_add_appointment" /> 
<include layout="@layout/activity_add_history" /> 
<include layout="@layout/activity_appointments" /> 
<include layout="@layout/activity_dog_profile" /> 
<include layout="@layout/activity_history" /> 
<include layout="@layout/activity_home" /> 
<include layout="@layout/activity_home_activity_listview" /> 
<include layout="@layout/activity_login" /> 
<include layout="@layout/activity_new_dog" /> 
<include layout="@layout/activity_registration" /> 
<include layout="@layout/activity_splash_screen" /> 
<include layout="@layout/activity_update_dog" /> 

</android.support.design.widget.CoordinatorLayout>

----------------------- homeactivitylistview.xml ---------------------- ---

public class HomeActivityListview extends AppCompatActivity { 

    ListView lv; 
    Context context; 
    ArrayList dogName; 
    ArrayList dogID; 
    public static int [] dogImages={R.drawable.dogpic}; 
    public static String [] dogNames={}; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_home_activity_listview); 
     Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 

     context=this; 

     lv=(ListView) findViewById(R.id.listView); 
     lv.setAdapter(new CustomAdapter(this, dogImages)); 
    } 


@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) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 


public void sendProfile(View view) { 
     Intent intent = new Intent(getApplicationContext(), DogProfileActivity.class); 
     startActivity(intent); 

    } 

    public void NumberOne(View view) { 
     AlertDialog.Builder alertDlg = new AlertDialog.Builder(this); 
     alertDlg.setMessage("Confirm Dog went number one"); 
     alertDlg.setCancelable(false); 

     alertDlg.setPositiveButton("Confirm", new DialogInterface.OnClickListener() { 
      @Override 
      public void onClick(DialogInterface dialog, int which) { 
       //HomeActivity.super.onBackPressed(); 
      } 
     }); 

     alertDlg.setNegativeButton("Change", new DialogInterface.OnClickListener(){ 

      @Override 
      public void onClick(DialogInterface dialog, int which) { 
       //HomeActivity.super.onBackPressed(); 
      } 
     }); 
     alertDlg.create().show(); 

    } 
    public void NumberTwo(View view) { 
     AlertDialog.Builder alertDlg = new AlertDialog.Builder(this); 
     alertDlg.setMessage("Confirm Dog went number two"); 
     alertDlg.setCancelable(false); 

     alertDlg.setPositiveButton("Confirm", new DialogInterface.OnClickListener() { 
      @Override 
      public void onClick(DialogInterface dialog, int which) { 
       //HomeActivity.super.onBackPressed(); 
      } 
     }); 

     alertDlg.setNegativeButton("Change", new DialogInterface.OnClickListener(){ 

      @Override 
      public void onClick(DialogInterface dialog, int which) { 
       //HomeActivity.super.onBackPressed(); 
      } 
     }); 
     alertDlg.create().show(); 

    } 

    public void AddNewDog(View view) { 
     Intent intent = new Intent(getApplicationContext(), NewDogActivity.class); 
     startActivity(intent); 
    } 

}

------------------ main_activity.java -----------------

public class MainActivity extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

} 

@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) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 
}

-------------- homelistview.java ------------------

public class HomeActivityListview extends AppCompatActivity { 

    ListView lv; 
    Context context; 
    ArrayList dogName; 
    ArrayList dogID; 
    public static int [] dogImages={R.drawable.dogpic}; 
    public static String [] dogNames={}; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_home_activity_listview); 
     Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 

     context=this; 

     lv=(ListView) findViewById(R.id.listView); 
     lv.setAdapter(new CustomAdapter(this, dogImages)); 
    } 


@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) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 


public void sendProfile(View view) { 
     Intent intent = new Intent(getApplicationContext(), DogProfileActivity.class); 
     startActivity(intent); 

    } 

    public void NumberOne(View view) { 
     AlertDialog.Builder alertDlg = new AlertDialog.Builder(this); 
     alertDlg.setMessage("Confirm Dog went number one"); 
     alertDlg.setCancelable(false); 

     alertDlg.setPositiveButton("Confirm", new DialogInterface.OnClickListener() { 
      @Override 
      public void onClick(DialogInterface dialog, int which) { 
       //HomeActivity.super.onBackPressed(); 
      } 
     }); 

     alertDlg.setNegativeButton("Change", new DialogInterface.OnClickListener(){ 

      @Override 
      public void onClick(DialogInterface dialog, int which) { 
       //HomeActivity.super.onBackPressed(); 
      } 
     }); 
     alertDlg.create().show(); 

    } 
    public void NumberTwo(View view) { 
     AlertDialog.Builder alertDlg = new AlertDialog.Builder(this); 
     alertDlg.setMessage("Confirm Dog went number two"); 
     alertDlg.setCancelable(false); 

     alertDlg.setPositiveButton("Confirm", new DialogInterface.OnClickListener() { 
      @Override 
      public void onClick(DialogInterface dialog, int which) { 
       //HomeActivity.super.onBackPressed(); 
      } 
     }); 

     alertDlg.setNegativeButton("Change", new DialogInterface.OnClickListener(){ 

      @Override 
      public void onClick(DialogInterface dialog, int which) { 
       //HomeActivity.super.onBackPressed(); 
      } 
     }); 
     alertDlg.create().show(); 

    } 

    public void AddNewDog(View view) { 
     Intent intent = new Intent(getApplicationContext(), NewDogActivity.class); 
     startActivity(intent); 
    } 

}

--- ------------ androidmanifest -----------------

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
package="cs495capstone.edu.bsu.doggydid" > 

<uses-permission android:name="android.permission.INTERNET" /> 

<application 
    android:allowBackup="true" 
    android:icon="@mipmap/ic_launcher" 
    android:label="@string/app_name" 
    android:supportsRtl="true" 
    android:theme="@style/AppTheme" > 
    <activity android:name=".SplashScreenActivity" > 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
    <activity 
     android:name=".RegistrationActivity" 
     android:label="Registration" /> 
    <activity 
     android:name=".NewDogActivity" 
     android:label="Dog Information" /> 
    <activity 
     android:name=".LoginActivity" 
     android:label="Login" /> 
    <activity 
     android:name=".HomeActivity" 
     android:label="@string/title_activity_home" /> 
    <activity 
     android:name=".DogProfileActivity" 
     android:label="@string/title_activity_dog_profile" /> 
    <activity 
     android:name=".HistoryActivity" 
     android:label="@string/title_activity_records" /> 
    <activity 
     android:name=".addHistoryActivity" 
     android:label="@string/title_activity_add_record" /> 
    <activity 
     android:name=".EventsActivity" 
     android:label="@string/title_activity_events" /> 
    <activity 
     android:name=".addEventsActivity" 
     android:label="@string/title_activity_add_events" /> 
    <activity 
     android:name=".UpdateDogActivity" 
     android:label="@string/title_activity_update_dog" /> 
    <activity 
     android:name=".HomeActivityListview" 
     android:label="@string/title_activity_home_activity_listview" 
     android:theme="@style/AppTheme.NoActionBar"> 
    </activity> 
</application> 

</manifest>

-----------------------錯誤讀數--------------------

04-14 13：35：36.905 3117-3117/cs495capstone.edu.bsu.doggydid E/AndroidRuntime：致命異常：主工藝：cs495capstone.edu.bsu.doggydid，PID：3117 了java.lang.RuntimeException ：無法啓動活動ComponentInfo {cs495capstone.edu.bsu.doggydid/cs495capstone.edu.bsu.doggydid.HomeActivityListview}：java.lang.NullPointerException：試圖調用虛擬方法'java.lang.CharSequence android.support.v7.widget .Toolbar.getTitle（）'在空對象引用 at android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2298）在android.app.ActivityThread.access $ 800（ActivityThread.java:144） at android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1278））在android.os.Handler.dispatchMessage（Handler.java:102） at android.os.Looper.loop（Looper.java:135） at android.app.ActivityThread.main（ActivityThread.java:5221）在java.lang.reflect.Method.invoke（Native Method） at java.lang.reflect.Method.invoke（Method。（ZygoteInit.java:694）由於： java.lang.NullPointerException：嘗試在android.support.v7.widget.ToolbarWidgetWrapper的空對象引用上調用虛擬方法'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle（）'（ToolbarWidgetWrapper .java：98） at android.support.v7.widget.ToolbarWidgetWrapper。（ToolbarWidgetWrapper.java:91） at android.support.v7.app.ToolbarActionBar。（ToolbarActionBar.java:73） at android.support.v7 .app.AppCompatDelegateImplV7.setSupportActionBar（AppCo mpatDelegateImplV7.java:205） at android.support.v7.app.AppCompatActivity.setSupportActionBar（AppCompatActivity.java:99） at cs495capstone.edu.bsu.doggydid.HomeActivityListview.onCreate（HomeActivityListview.java:31） at android。 app.Activity.performCreate（Activity.java:5933） at android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1105） at android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2251） at android.app。 Activity.Thread.handleLaunchActivity（ActivityThread.java:2360） at android.app.ActivityThread.access $ 800（ActivityThread.java:144） at andro id.app.ActivityThread $ H.handleMessage（ActivityThread.java:1278） at android.os.Handler.dispatchMessage（Handler.java:102） at android.os.Looper.loop（Looper.java:135） at android.app.ActivityThread.main（ActivityThread.java:5221） at java.lang.reflect.Method.invoke（Native Method） at java.lang.reflect.Method.invoke（Method.java:372） at com .android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:899）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:694）

來源

2016-04-14 shadowice0823

它看起來像你設置初始化'HomeActivityListview'和'MainActivity'中的'Toolbar'。您粘貼的XML文件看起來像是由'tools：context =「cs495capstone.edu.bsu.myapplication.HomeActivityListview」'判斷的'HomeActivityListview'的佈局文件。你可以驗證'activity_main.xml'包含一個''工具欄'與'ID'「R.id.toolbar」？ – Ryan

這可能是它看着有一個工具欄作爲一個自定義的應用程序欄佈局和工具欄的新項目，然後看我的編輯XML沒有創建這些。當我試圖在設計視圖中添加它們時，它是固執的 – shadowice0823

是的，'設計'模式可能有點笨重。我建議在需要進行更改時使用XML文件的「文本」編輯模式。 – Ryan

工具欄工具欄是德只有clared /初始化在OnCreate，因此範圍出去了該方法的...

定義對象作爲活動變量和onCreate

public class HomeActivityListview extends AppCompatActivity { 

    ListView lv; 
    Context context; 
    ArrayList dogName; 
    ArrayList dogID; 
    public static int [] dogImages={R.drawable.dogpic}; 
    public static String [] dogNames={}; 
    private Toolbar toolbar; //define it here 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_home_activity_listview); 
     toolbar = (Toolbar) findViewById(R.id.toolbar); //but init here 
     setSupportActionBar(toolbar); 

     context=this; 

     lv=(ListView) findViewById(R.id.listView); 
     lv.setAdapter(new CustomAdapter(this, dogImages)); 
    }

來源

2016-04-14 18:16:19

如果我刪除工具欄中的工具欄，工具欄=（工具欄）findViewByID（R.id.toolbar）;它會拋出一個錯誤，並希望我在那裏初始化它，然後將工具欄添加回 – shadowice0823

如何刪除它？ –

結束瞭解決它。在我的activity_main xml類中，我只在xml中編碼，當我在設計模式下查看時，它沒有顯示appbarlayout或toolbar選項 – shadowice0823

實現工具欄調用空對象引用

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