我试图将ViewPager添加到我的项目中，但存在问题

Question

该问题是由以下原因引起的：

java.lang.ArrayIndexOutOfBoundsException： 长度=0;索引=0

at com.example.proje.DetayActivity.onCreate(DetayActivity.java：78(

在此页面中，我添加了要在活动中显示的视图页。我认为数组列表有问题，但它看起来很正常，因为我找不到任何问题。谢谢你的帮助。

---

package com.example.proje;
imports..
public class DetayActivity extends AppCompatActivity {
ViewPager viewPager;
LinearLayout sliderDotspanel;
private int dotscount;
private ImageView[] dots;
private ArrayList<String> urls;
String key;
TextView txt1;
TextView txt2;
TextView txt3;
TextView txt4;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detay);
setTitle("Detaylar");
txt1 = findViewById(R.id.txttarih);
txt2 = findViewById(R.id.txturunadi);
txt3 = findViewById(R.id.txtfiyati);
txt4 = findViewById(R.id.txtaciklama);
Intent intent = getIntent();
key = intent.getStringExtra("key");
urls = new ArrayList<>();
getdata();

viewPager = findViewById(R.id.viewPager);
sliderDotspanel = findViewById(R.id.SliderDots);

ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(this , urls);
viewPager.setAdapter(viewPagerAdapter);
dotscount = viewPagerAdapter.getCount();
dots = new ImageView[dotscount];
for (int i = 0; i < dotscount; i++) {
dots[i] = new ImageView(this);
dots[i].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.non_active_dot));
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
params.setMargins(8, 0, 8, 0);
sliderDotspanel.addView(dots[i], params);
}
dots[0].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.active_dot));
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
for (int i = 0; i < dotscount; i++) {
dots[i].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.non_active_dot));
}
dots[position].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.active_dot));
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
}
private void getdata() {
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("urunler").child(key);
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
Urun urun = dataSnapshot.getValue(Urun.class);
txt1.setText(urun.getTarih());
txt2.setText(urun.getUrunAdi());
txt3.setText(Double.toString(urun.getFiyat()));
txt4.setText(urun.getAciklama());
urls.add(urun.getResim1());
urls.add(urun.getResim2());
urls.add(urun.getResim3());
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}

此页面是查看页适配器

package com.example.proje;
imports..
public class ViewPagerAdapter extends PagerAdapter {
private Context context;
private LayoutInflater layoutInflater;
private Integer [] images = {R.drawable.logo,R.drawable.doluredkalp,R.drawable.redheart};
private ArrayList<String> urls = new ArrayList<>();

public ViewPagerAdapter(Context context , ArrayList<String> urls) {
this.context = context;
this.urls = urls;
}
@Override
public int getCount() {
return urls.size();
}
@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
@Override
public Object instantiateItem(ViewGroup container, final int position) {
final String url = urls.get(position);
layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View view = layoutInflater.inflate(R.layout.layoutpager, null);
ImageView imageView = view.findViewById(R.id.imageView);    
Picasso.get().load(url).placeholder(R.drawable.logo).into(imageView);
ViewPager vp = (ViewPager) container;
vp.addView(view, 0);
return view;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
ViewPager vp = (ViewPager) container;
View view = (View) object;
vp.removeView(view);
}
}

Answer 1

你的问题符合要求

dots[0].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.active_dot));

数组dots为空，当您尝试获取索引 0 处的元素时，会出现此错误，因为索引 0 处没有元素。

更新：

您可以看到点是一个计数等于dotscount的数组。

dotscount变量是viewPagerAdapter项的计数

你传递给视图PagerAdapterurls数组，它是空的。

这就是您收到错误的原因ArrayIndexOutOfBoundsException

我认为您应该在填充数组后onDataChange方法中创建dots数组urls这将修复此错误