Question

我想创建一个包含2个标签的viewpager，我有3个布局：

这是包含纸张的activity_chart.xml：

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</android.support.v4.view.ViewPager>

这是AccountsActivityChart.java：

import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;

import com.rastari.salar.mymetarialbank.R;
import com.rastari.salar.mymetarialbank.adapter.TabsPagerAdapter;

/**
 * Created by Salar on 9/5/2015.
 */
public class AccountsActivityChart extends FragmentActivity implements ActionBar.TabListener {

    private ViewPager viewPager;
    private TabsPagerAdapter mAdapter;
    private ActionBar actionBar;
    // Tab titles
    private String[] tabs = { "Accounts Activity", "Chart Activity" };

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

        // Initilization
        viewPager = (ViewPager) findViewById(R.id.pager);
        actionBar = getActionBar();
        mAdapter = new TabsPagerAdapter(getSupportFragmentManager());

        viewPager.setAdapter(mAdapter);
        actionBar.setHomeButtonEnabled(false);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        // Adding Tabs
        for (String tab_name : tabs) {
            actionBar.addTab(actionBar.newTab().setText(tab_name)
                    .setTabListener(this));
        }

        /**
         * on swiping the viewpager make respective tab selected
         * */
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

            @Override
            public void onPageSelected(int position) {
                // on changing the page
                // make respected tab selected
                actionBar.setSelectedNavigationItem(position);
            }

            @Override
            public void onPageScrolled(int arg0, float arg1, int arg2) {
            }

            @Override
            public void onPageScrollStateChanged(int arg0) {
            }
        });
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
        // on tab selected
        // show respected fragment view
        viewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {
    }
}

这是TabsPagerAdapter.java类：

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;


/**
 * Created by Salar on 26/4/2015.
 */
public class TabsPagerAdapter extends FragmentPagerAdapter {
    public TabsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int index) {

        switch (index) {
            case 0:
                // Accounts Activity fragment activity
                return new AccountsActivityFragment();
            case 1:
                // Chart Activity activity
                return new ChartActivityFragment();
        }
        return null;
    }

    @Override
    public int getCount() {
        // get item count - equal to number of tabs
        return 2;
    }

}

这是AccountsActivityFragment.java：

import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.rastari.salar.mymetarialbank.R;

/**
 * Created by Salar on 25/4/2015.
 */
public class AccountsActivityFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_accounts_activity, container, false);

        return rootView;
    }
}

这是ChartActivityFragment.java：

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.rastari.salar.mymetarialbank.R;

/**
 * Created by Salar on 9/5/2015.
 */
public class ChartActivityFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_chart_activity, container, false);

        return rootView;
    }
}

这很明显：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.rastari.salar.mymetarialbank" >

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/MyMetarialBank">
        <activity
            android:name=".activity.Login"
            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=".activity.MainActivity"/>
        <activity android:name=".activity.AccountsActivityChart"/>
    </application>

</manifest>

当我运行应用程序时，我收到此错误：

尝试调用虚方法＆＃39; void android.app.ActionBar.setHomeButtonEnabled（布尔值）＆＃39;在null对象上参考

我该如何解决这个问题？

Answer 1

我认为您已经应用了没有操作栏的主题。这就是为什么当您获取操作栏实例时，它将为null并且您在null操作栏实例上调用setHomeButtonEnabled。这就是你收到错误的原因。

Answer 2

尝试actionBar = getSupportActionBar（）; 而不是actionBar = getActionBar（）;

什么是ActionBar.setHomeButtonEnabled（boolean）

2 个答案: