Question

我试图从firebase中恢复四张照片，并将它们显示在幻灯片中，并使用getUrl()来检索URL。

但是，setSliderViews()方法无法执行，并且我看到此错误：

致命异常：main：”

如何解决此问题？

public class MainActivity extends AppCompatActivity {


    Upload data;
    ArrayList<String> url = new ArrayList<String>();
    SliderLayout sliderLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        sliderLayout = findViewById(R.id.imageSlider);

        sliderLayout.setIndicatorAnimation(SliderLayout.Animations.FILL); //set indicator animation by using SliderLayout.Animations. :WORM or THIN_WORM or COLOR or DROP or FILL or NONE or SCALE or SCALE_DOWN or SLIDE and SWAP!!
        sliderLayout.setScrollTimeInSec(1); //set scroll delay in seconds :
        getUrl();
        setSliderViews();
    }
    private void  getUrl(){

        final ArrayList<String> mUrl = new ArrayList<String>();

        FirebaseDatabase.getInstance().getReference("upload").addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                    data = snapshot.getValue(Upload.class);

                    if (data != null) {
                        mUrl.add(data.getImageUrl());
                    }
                }
                url = mUrl;
            }
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }
    private void setSliderViews() {

        for (int i = 0; i <= 3; i++) {

            SliderView sliderView = new SliderView(this);
                switch (i) {
                    case 0:
                        sliderView.setImageUrl(url.get(0));
                        break;
                    case 1:
                        sliderView.setImageUrl(url.get(1));
                        break;
                    case 2:
                        sliderView.setImageUrl(url.get(2));
                        break;
                    case 3:
                        sliderView.setImageUrl(url.get(3));
                        break;
                }


            sliderView.setImageScaleType(ImageView.ScaleType.CENTER_CROP);
            //sliderView.setDescription(" " + (i + 1));
            final int finalI = i;
            sliderView.setOnSliderClickListener(new SliderView.OnSliderClickListener() {
                @Override
                public void onSliderClick(SliderView sliderView) {
                    Toast.makeText(MainActivity.this, "This is slider " + (finalI + 1), Toast.LENGTH_SHORT).show();
                }
            });

            //at last add this view in your layout :
            sliderLayout.addSliderView(sliderView);
        }

    }

    }

This screen from lolcat describe error

Answer 1

addListenerForSingleValueEvent不会立即执行，因此在您的setSliderViews()被称为'url'ArrayList时是空的。您需要等待侦听器执行。

查看此线程： wait until firebase retrieves data

使用Firebase中的图片网址制作幻灯片

1 个答案: