ViewPager 及其 Indicator 不可见

Question

我正在尝试使用 CardView 显示一些新闻。在这些之上，将有一个 ViewPager 和 ViewPager Indicator，用于显示广告。这些是相关代码。

fragment_news.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context="net.devbyzero.app.school.fragment.NewsFragment">


    <!-- for displaying ads -->
    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

    <LinearLayout
        android:id="@+id/llDots"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_marginTop="10dp"
        android:gravity="center"
        android:orientation="horizontal" >
    </LinearLayout>


    <!-- for displaying news -->
    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">
                <android.support.v7.widget.RecyclerView
                    android:id="@+id/news_list"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    />
        </LinearLayout>

</FrameLayout>

vp_item.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center"
    android:padding="10dp" >

    <ImageView
        android:id="@+id/flag"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:contentDescription="@string/app_name"
        android:padding="1dp" />

</RelativeLayout>

ViewPagerAdapter.java

import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.RelativeLayout;

public class ViewPagerAdapter extends PagerAdapter {

    Context context;
    int[] flag;
    LayoutInflater inflater;

    public ViewPagerAdapter(Context context, int[] flag){
        this.context = context;
        this.flag = flag;
    }

    @Override
    public int getCount() {
        return flag.length;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return (view == (RelativeLayout) object);
    }

    @Override
    public float getPageWidth(int position) {
        return 0.7f;
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        ImageView imgflag;

        inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View itemView = inflater.inflate(R.layout.vp_item, container,false);

        // Locate the ImageView in vp_item.xml
        imgflag = (ImageView) itemView.findViewById(R.id.flag);
        // Capture position and set to the ImageView
        imgflag.setImageResource(flag[position]);

        // Add viewpager_item.xml to ViewPager
        ((ViewPager) container).addView(itemView);

        return itemView;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        // Remove viewpager_item.xml from ViewPager
        ((ViewPager) container).removeView((RelativeLayout) object);
    }
}

NewsFragment.java

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import android.widget.LinearLayout.LayoutParams;

import net.devbyzero.app.school.NewsListAdapter;
import net.devbyzero.app.school.R;
import net.devbyzero.app.school.ViewPagerAdapter;
import net.devbyzero.app.school.data.NewsProvider;

import java.util.ArrayList;

public class NewsFragment extends Fragment {

    private RecyclerView recView;
    private NewsListAdapter adapter;
    private ViewPager vPager;
    private PagerAdapter pAdapter;
    private LinearLayout llDots;

    public static NewsFragment newInstance(String param1, String param2){
        NewsFragment fragment = new NewsFragment();
        return fragment;
    }

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

        View view = inflater.inflate(R.layout.fragment_news, container, false);
        recView = (RecyclerView) view.findViewById(R.id.news_list);
        recView.setLayoutManager(new LinearLayoutManager(getActivity()));

        vPager = (ViewPager) view.findViewById(R.id.pager);
        llDots = (LinearLayout) view.findViewById(R.id.llDots);
        int[] banners = new int[]{R.drawable.banner1, R.drawable.banner2, R.drawable.banner3};
        pAdapter = new ViewPagerAdapter(getActivity(), banners);
        vPager.setAdapter(pAdapter);

        for (int x = 0; x < pAdapter.getCount(); x++){
            ImageButton imgDot = new ImageButton(getActivity());
            imgDot.setTag(x);
            imgDot.setImageResource(R.drawable.dot_selector);
            imgDot.setBackgroundResource(0);
            imgDot.setPadding(5, 5, 5, 5);
            LayoutParams params = new LayoutParams(20, 20);
            imgDot.setLayoutParams(params);
            if(x == 0) imgDot.setSelected(true);
            llDots.addView(imgDot);
        }

        ((AppCompatActivity)getActivity()).getSupportActionBar().setTitle("News");

        adapter = new NewsListAdapter(new NewsProvider().getNews());
        recView.setAdapter(adapter);
        return view;
    }
}

CardView 部分工作正常。但不是 ViewPager 和指示器。它们根本没有显示。诡异的。顺便说一句，ViewPager 代码取自 this site.

那怎么解决呢？

Answer 1

Use LinearLayout in place of FrameLayout with vertical orientation

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:weightSum="3">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1.5"
        android:orientation="vertical"
        android:weightSum="1.5">

        <!-- for displaying ads -->
        <android.support.v4.view.ViewPager
            android:id="@+id/pager"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1.0" />

        <LinearLayout
            android:id="@+id/llDots"
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:layout_weight="0.5"
            android:gravity="center"
            android:background="@android:color/black"
            android:orientation="horizontal" />

    </LinearLayout>


    <!-- for displaying news -->
    <android.support.v7.widget.RecyclerView
        android:id="@+id/news_list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1.5" />


</LinearLayout>

您可以根据需要space为特定的小部件管理权重值。

Answer 2

上面需要布局来实现这样的概念。因此，您必须使用 LinearLayout 而不是 FrameLayout。此外，您没有将适配器设置为 ViewPager，因此无论如何高度都将为 0。

ViewPager 及其 Indicator 不可见

ViewPager and its Indicator are not visible

android

android-viewpager

viewpagerindicator