Question

我是第一次在android中尝试Fragments，我使用FragmentPagerAdapter来获取有限数量的片段，在这种情况下是3.唯一的问题是，当我滑动时，它会进入第二页和第三页，但是每次都显示第一个片段的布局，而不是另一个片段。

MainActivity.java：

package com.example.swipetabtest;

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.support.v4.view.ViewPager.OnPageChangeListener;
import android.widget.Toast;

public class MainActivity extends FragmentActivity {
    FragmentPagerAdapter adapterViewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ViewPager vpPager = (ViewPager) findViewById(R.id.vpPager);
        adapterViewPager = new MyPagerAdapter(getSupportFragmentManager());
        vpPager.setAdapter(adapterViewPager);
    }

    public static class MyPagerAdapter extends FragmentPagerAdapter {
    private static int NUM_ITEMS = 3;

        public MyPagerAdapter(FragmentManager fragmentManager) {
            super(fragmentManager);
        }

        // Returns total number of pages
        @Override
        public int getCount() {
            return NUM_ITEMS;
        }

        // Returns the fragment to display for that page
        @Override
        public Fragment getItem(int position) {
            switch (position) {
            case 0:
                return FirstFragment.newInstance(0, "Page # 1");
            case 1:
                return SecondFragment.newInstance(1, "Page # 2");
            case 2:
                return ThirdFragment.newInstance(2, "Page # 3");
            default:
                return null;
            }
        }

    }

}

FirstFragment.java

package com.practice.swipetabtest;

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

public class FirstFragment extends Fragment {
    // Store instance variables
    private String title;
    private int page;

    // newInstance constructor for creating fragment with arguments
    public static FirstFragment newInstance(int page, String title) {
        FirstFragment fragmentFirst = new FirstFragment();
        Bundle args = new Bundle();
        args.putInt("someInt", page);
        args.putString("someTitle", title);
        fragmentFirst.setArguments(args);
        return fragmentFirst;
    }

    // Store instance variables based on arguments passed
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        page = getArguments().getInt("someInt", 0);
        title = getArguments().getString("someTitle");
    }

    // Inflate the view for the fragment based on layout XML
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_first, container, false);
        return view;
    }
}

SecondFragment.java

package com.practice.swipetabtest;

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

public class SecondFragment extends Fragment {
    // Store instance variables
    private String title;
    private int page;

    // newInstance constructor for creating fragment with arguments
    public static FirstFragment newInstance(int page, String title) {
        FirstFragment fragmentFirst = new FirstFragment();
        Bundle args = new Bundle();
        args.putInt("someInt", page);
        args.putString("someTitle", title);
        fragmentFirst.setArguments(args);
        return fragmentFirst;
    }

    // Store instance variables based on arguments passed
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        page = getArguments().getInt("someInt", 1);
        title = getArguments().getString("someTitle");
    }

    // Inflate the view for the fragment based on layout XML
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_second, container, false);
        return view;
    }
}

ThirdFragment.java

package com.practice.swipetabtest;

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

public class ThirdFragment extends Fragment {
    // Store instance variables
    private String title;
    private int page;

    // newInstance constructor for creating fragment with arguments
    public static FirstFragment newInstance(int page, String title) {
        FirstFragment fragmentFirst = new FirstFragment();
        Bundle args = new Bundle();
        args.putInt("someInt", page);
        args.putString("someTitle", title);
        fragmentFirst.setArguments(args);
        return fragmentFirst;
    }

    // Store instance variables based on arguments passed
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        page = getArguments().getInt("someInt", 2);
        title = getArguments().getString("someTitle");
    }

    // Inflate the view for the fragment based on layout XML
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_third, container, false);
        return view;
    }
}

activity_main.xml中：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <android.support.v4.view.ViewPager
        android:id="@+id/vpPager"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    </android.support.v4.view.ViewPager>
</LinearLayout>

fragment_first.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView 
        android:text="this is the first fragment"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>

fragment_second.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:text="this is the second fragment"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>

fragment_third.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:text="hey look a third fragment"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>

我尝试检查一些显而易见的事情，例如每个片段是否正确的布局是否膨胀，以及switch语句是否适用于正确的片段，但它们看起来也不错......

但它会不断显示第一个片段的布局。

Answer 1

问题是，如果你看一下你的FirstFragment，SecondFragment和ThirdFragment类instantiateFragment方法，你实际上是在所有这三个方法中创建一个新的FirstFragment实例。

您正在致电：

        FirstFragment fragmentFirst = new FirstFragment();

在所有三个课程中，您应该致电：

        SecondFragment fragmentSecond = new SecondFragment();

或

        ThirdFragment fragmentThird = new ThirdFragment();

取决于您所在的班级。

Answer 2

@Override
        public Fragment getItem(int position) {
            switch (position) 
           {
              Fragment frag=null;
        if(position==0)
            frag=new FirstFragment();
        if(position==1)
            frag=new SecondFragment();
        if(position==2)
            frag=new ThirdFragment();

        return frag;
            }

FragmentActivity没有显示片段的正确布局

2 个答案: