Question

出于某种原因，我刚刚开始的项目似乎让我很紧张。我显然不知道为什么，我的应用程序不会运行。这是我的MainActivity的代码：

package com.example.testarearg;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class MainActivity extends FragmentActivity   {

/**
 * The {@link android.support.v4.view.PagerAdapter} that will provide
 * fragments for each of the sections. We use a
 * {@link android.support.v4.app.FragmentPagerAdapter} derivative, which
 * will keep every loaded fragment in memory. If this becomes too memory
 * intensive, it may be best to switch to a
 * {@link android.support.v4.app.FragmentStatePagerAdapter}.
 */
SectionsPagerAdapter mSectionsPagerAdapter;

/**
 * The {@link ViewPager} that will host the section contents.
 */
ViewPager mViewPager;

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


    // For each of the sections in the app, add a tab to the action bar.
    for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
        // Create a tab with text corresponding to the page title defined by
        // the adapter. Also specify this Activity object, which implements
        // the TabListener interface, as the callback (listener) for when
        // this tab is selected.

    }
}




/**
 * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
 * one of the sections/tabs/pages.
 */
public class SectionsPagerAdapter extends FragmentPagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a DummySectionFragment (defined as a static inner class
        // below) with the page number as its lone argument.
        Fragment fragment = new DummySectionFragment();
        Bundle args = new Bundle();
        args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
        fragment.setArguments(args);
        return fragment;
    }


    @Override
    public int getCount() {
        // Show 3 total pages.
        return 3;
    }


}

/**
 * A dummy fragment representing a section of the app, but that simply
 * displays dummy text.
 */
public static class DummySectionFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */ private String mText; // display this text in your fragment

     public static Fragment getInstance(String text) {
       Fragment f = new Fragment();
       Bundle args = new Bundle();
       args.putString("text", text);
       f.setArguments(args);
       return f;
     }

     public void onCreate(Bundle state) {
       super.onCreate(state);
       setmText(getArguments().getString("text"));
       // rest of your code
     }

    public static final String ARG_SECTION_NUMBER = "section_number";

    public DummySectionFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main_dummy, container, false);
        TextView dummyTextView = (TextView) rootView.findViewById(R.id.section_label);
        dummyTextView.setText(Integer.toString(getArguments().getInt(ARG_SECTION_NUMBER)));
        return rootView;
    }

    public String getmText() {
        return mText;
    }

    public void setmText(String mText) {
        this.mText = mText;
    }
}

}

这是我的logcat日志的截图。 http://s23.postimg.org/imxwv32ez/5555.jpg

Answer 1

此行有一个NullPointerException：

for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {

因为mSectionsPagerAdapter永远不会在您的代码中初始化

Answer 2

mSectionsPagerAdapter.getCount()

返回null，因为您从未将mSectionsPagerAdapter初始化为任何内容

Answer 3

问题是NullPointerException。 mSectionsPagerAdapter为空。您需要在使用之前对其进行初始化。

申请无法启动

3 个答案: