android - 为什么 getActionBar() 从 Android 获取 TabHost 中的空值？

标签 android nullpointerexception android-actionbar android-tabactivity

我正在尝试在 Android 中编写代码，以在向下滚动事件期间隐藏 Actionbar。我有一个 10x50 的网格。所以当我向下滚动时，操作栏应该隐藏。我在 Log Cat 中正确获得滚动状态结果，所以每当我申请 getActionBar().hide 时，我都会收到 NullPointerException 错误。

我的代码: 

package com.example.complexdatepicker;

import android.app.TabActivity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TabHost;
import android.widget.TabHost.TabSpec;

public class MainActivity extends TabActivity 
{

@Override
protected void onCreate(Bundle savedInstanceState) 
{


        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        TabHost tabHost = getTabHost();


        TabSpec tab1 = tabHost.newTabSpec("Home");

        tab1.setIndicator("Home");
        Intent photosIntent = new Intent(this, Home.class);
        tab1.setContent(photosIntent);

        tabHost.addTab(tab1);


}

 }

Home.java

package com.example.complexdatepicker;

import java.util.ArrayList;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.widget.GridView;


public class Home extends ActionBarActivity 
{

ArrayList<String> abc;

TestGrid tg;

GridView gv;

int mLastFirstVisibleItem;

int mLastVisibleItemCount;

@Override
protected void onCreate(Bundle savedInstanceState) 
{


        super.onCreate(savedInstanceState);

        setContentView(R.layout.home);

        gv = (GridView) findViewById(R.id.gridView1);

        abc = new ArrayList<String>();

        for(int i=0;i<500;i++)
        {

            abc.add(String.valueOf(i));

        }


        tg = new TestGrid(Home.this,Home.this,abc);

        gv.setAdapter(tg);

        getSupportActionBar().hide(); /// Getting Error at this point..


     /*         
        gv.setOnScrollListener(new AbsListView.OnScrollListener() {
            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                if (mLastFirstVisibleItem > firstVisibleItem) {
                    Log.e(getClass().toString(), "scrolling up");
                    getActionBar().show();
                } else if (mLastFirstVisibleItem < firstVisibleItem) {
                    Log.e(getClass().toString(), "scrolling down");
                    getActionBar().hide();

                } else if (mLastVisibleItemCount < visibleItemCount) {
                    Log.e(getClass().toString(), "scrolling down");
                    getActionBar().hide();
                } else if (mLastVisibleItemCount > visibleItemCount) {
                    Log.e(getClass().toString(), "scrolling up");
                    getActionBar().show();
                }
                mLastFirstVisibleItem = firstVisibleItem;
                mLastVisibleItemCount = visibleItemCount;
            }

            public void onScrollStateChanged(AbsListView listView, int scrollState) {
            }
        });

     */         

}

 }

TestGrid.java

package com.example.complexdatepicker;
import java.util.ArrayList;
import java.util.Calendar;
import android.annotation.SuppressLint;
import android.app.DatePickerDialog;
import android.app.Dialog;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.app.DialogFragment;
import android.support.v4.app.FragmentActivity;
import android.util.Log;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.View.OnClickListener;
import android.widget.BaseAdapter;
import android.widget.DatePicker;
import android.widget.TextView;
import android.widget.Toast;

public class TestGrid extends BaseAdapter
{

    private ArrayList<String> abc;

    private FragmentActivity activity;

    private Context context; 

    String text;

    int c = 0;

    int x = 0;

    SelectDateFragment newFragment;



    public TestGrid(FragmentActivity activity , Context cont,ArrayList<String> abc)
    {

        super();

        this.activity=activity;

        this.context = cont;

        this.abc = abc;

    }

    @Override
    public int getCount() 
    {

        return abc.size();

    }

    @Override
    public Object getItem(int in) 
    {       

        return abc.get(in);

    }

    @Override
    public long getItemId(int arg0) 
    {

        return 0;

    }

    public class ViewHolder
    {

        public TextView txt;

    }


    @Override
    public View getView(final int arg0, View arg1, ViewGroup arg2) 
    {

        final SharedPreferences pref = context.getApplicationContext().getSharedPreferences("TestDate", 0);

        ViewHolder view;

        LayoutInflater inflator = activity.getLayoutInflater();

        if(arg1==null)
        {

            view = new ViewHolder();

            arg1 = inflator.inflate(R.layout.test_grid, null);

            view.txt = (TextView) arg1.findViewById(R.id.txt);

            arg1.setTag(view);

        }
        else
        {

            view = (ViewHolder) arg1.getTag();

        }





         View.OnClickListener alert = new OnClickListener() 
         {


                public void onClick(View v) 
                {


                        Toast.makeText(activity.getApplicationContext(), abc.get(arg0)+" - Clicked ", Toast.LENGTH_SHORT).show();


                    newFragment = new SelectDateFragment();

                    Bundle args = new Bundle();

                    newFragment.setArguments(args);


                    newFragment.setOnDateSetListener(new DatePickerDialog.OnDateSetListener()
                    {

                        @Override
                        public void onDateSet(DatePicker view, int yy, int mm, int dd)
                        {

                            String saved_date = pref.getString("SavedDate", null);

                            Toast.makeText(activity.getApplicationContext(), "SavedDate : "+saved_date,Toast.LENGTH_LONG).show(); 


                        }


                    });



                    newFragment.show(activity.getSupportFragmentManager(), "DatePicker");       

                }


         };



        view.txt.setOnClickListener(alert);






        text = String.valueOf(abc.get(arg0));

        view.txt.setBackgroundResource(R.drawable.txtbk);

        view.txt.setTextSize(18);

        view.txt.setTextColor(Color.BLACK);

        view.txt.setGravity(Gravity.CENTER);    

        view.txt.setText(text);

        return arg1;

    }




    @SuppressLint({ "ValidFragment", "NewApi" })
    public class SelectDateFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener 
    {


        private DatePickerDialog.OnDateSetListener externalListener;

        public void setOnDateSetListener(DatePickerDialog.OnDateSetListener listener)
        {
            this.externalListener = listener;
        }

        @Override
        public Dialog onCreateDialog(Bundle savedInstanceState) 
        {


                final Calendar calendar = Calendar.getInstance();

                int yy = calendar.get(Calendar.YEAR);

                int mm = calendar.get(Calendar.MONTH);

                int dd = calendar.get(Calendar.DAY_OF_MONTH);

                return new DatePickerDialog(getActivity(), this, yy, mm, dd);


        }


        public void onDateSet(DatePicker view, int yy, int mm, int dd)
        {

            SharedPreferences pref = context.getApplicationContext().getSharedPreferences("TestDate", 0);

            Editor et = pref.edit();

            et.putString("SavedDate", String.valueOf(dd+"/"+mm+"/"+yy));

            et.commit();

            Log.d("SavedDate : ", String.valueOf(dd+"/"+mm+"/"+yy));

            if(externalListener != null)


                externalListener.onDateSet(view, yy, mm, dd);




        }


        public void onFinishEditDialog(String inputText) 
        {



        }


    }


}

AndroidManifest.xml

   <manifest 
     xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.example.complexdatepicker"
     android:versionCode="1"
     android:versionName="1.0" >

   <uses-sdk
      android:minSdkVersion="14"
      android:targetSdkVersion="17" />

  <application
      android:allowBackup="true"
      android:icon="@drawable/ic_launcher"
      android:label="@string/app_name"
      android:theme="@style/Theme.AppCompat" >

 <activity

        android:name="com.example.complexdatepicker.MainActivity"
        android:label="@string/app_name" >

     <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <activity
        android:name="com.example.complexdatepicker.Home"
        android:label="@string/app_name" ></activity>

 </application>

样式.xml

<resources>

<!--
    Base application theme, dependent on API level. This theme is replaced
    by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
-->
<style name="AppBaseTheme" parent="android:Theme.Light">
    <!--
        Theme customizations available in newer API levels can go in
        res/values-vXX/styles.xml, while customizations related to
        backward-compatibility can go here.
    -->
</style>

<!-- Application theme. -->
<style name="AppTheme" parent="AppBaseTheme">
    <!-- All customizations that are NOT specific to a particular API-level can go here. -->
</style>

     </resources>

错误图片:

enter image description here

错误:

05-25 11:10:37.374: E/AndroidRuntime(872): FATAL EXCEPTION: main
05-25 11:10:37.374: E/AndroidRuntime(872): java.lang.RuntimeException: Unable to start  activity ComponentInfo{com.example.complexdatepicker/com.example.complexdatepicker.MainActivity}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.complexdatepicker/com.example.complexdatepicker.Home}: java.lang.NullPointerException
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.os.Handler.dispatchMessage(Handler.java:99)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.os.Looper.loop(Looper.java:137)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.ActivityThread.main(ActivityThread.java:5103)
05-25 11:10:37.374: E/AndroidRuntime(872):  at java.lang.reflect.Method.invokeNative(Native Method)
05-25 11:10:37.374: E/AndroidRuntime(872):  at java.lang.reflect.Method.invoke(Method.java:525)
05-25 11:10:37.374: E/AndroidRuntime(872):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
05-25 11:10:37.374: E/AndroidRuntime(872):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-25 11:10:37.374: E/AndroidRuntime(872):  at dalvik.system.NativeStart.main(Native Method)
05-25 11:10:37.374: E/AndroidRuntime(872): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.complexdatepicker/com.example.complexdatepicker.Home}: java.lang.NullPointerException
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.ActivityThread.startActivityNow(ActivityThread.java:2054)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:135)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:347)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:749)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.widget.TabHost.setCurrentTab(TabHost.java:413)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.widget.TabHost.addTab(TabHost.java:240)
05-25 11:10:37.374: E/AndroidRuntime(872):  at com.example.complexdatepicker.MainActivity.onCreate(MainActivity.java:42)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.Activity.performCreate(Activity.java:5133)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
05-25 11:10:37.374: E/AndroidRuntime(872):  ... 11 more  
05-25 11:10:37.374: E/AndroidRuntime(872): Caused by: java.lang.NullPointerException
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.support.v7.app.ActionBarImplICS.hide(ActionBarImplICS.java:289)
05-25 11:10:37.374: E/AndroidRuntime(872):  at com.example.complexdatepicker.Home.onCreate(Home.java:50)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.Activity.performCreate(Activity.java:5133)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-25 11:10:37.374: E/AndroidRuntime(872):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
05-25 11:10:37.374: E/AndroidRuntime(872):  ... 21 more

这些都是上面的代码和错误详细信息，请告诉我如何在 TabWidget 中使用 getActionBar()。

请给我一些好的解决方案。

最佳答案

您的主页 Activity 必须扩展 ActionBarActivity 而不是 FragmentActivity 以便您可以调用 getActionBar() 方法。

ActionBarActivity 扩展 FragmentActivity。此外，您应该使用 getSupportActionBar() 而不是 getActionBar()，因为最新的要求 API 级别 11。

另请注意，您需要导入 v4 支持库才能调用 getSupportActionBar() 并支持 v7 库才能使用 ActionBarActivity。

关于android - 为什么 getActionBar() 从 Android 获取 TabHost 中的空值？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/23845738/

上一篇：java - Google Play 游戏服务解锁成就 - 在游戏中存储解锁或每次调用解锁()？

下一篇：android - 从 Android 上的相机录制视频到 mp4

相关文章：

android - 布局内部的 LinearLayout 与父级不匹配

java - 访问来自不同类的变量

java - 为什么Java中这段代码会抛出nullpointerException？

Android > 4.0 fragment 和标签

java - 使用 setRequestedOrientation() 时出现黑屏

Java - 填充 ArrayList 会出现空指针错误

java - 当我请求操作时，是什么导致了此 NPE？

android - 如何设置actionBar弹出背景？

android - StickyHeaderListView 与 ActionBarPullToRefresh 重叠

Android 自动更新不起作用

©2024 IT工具网  联系我们