如何将此代码更改为Kotlin以从Firebase数据库查看pdf

如何解决如何将此代码更改为Kotlin以从Firebase数据库查看pdf

如何将我的Java代码更改为kotlin代码，以从Firebase数据库中查看pdf

公共类javaclasActivity扩展了AppCompatActivity {

private TextView text1;
private PDFView pdfView;
private FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference mref = database.getReference("url");

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

    pdfView = (PDFView) findViewById(R.id.pdfView33);
    text1 = (TextView) findViewById(R.id.text11);

    mref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            String value = dataSnapshot.getValue(String.class);
            text1.setText(value);
            Toast.makeText(javaclasActivity.this,"updated",Toast.LENGTH_SHORT).show();
            String url = text1.getText().toString();
            new RetrivePdfStream().execute(url);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
            Toast.makeText(javaclasActivity.this,"failed to load",Toast.LENGTH_SHORT).show();
        }
    });}

///我在下面的这段代码中遇到了麻烦

    class RetrivePdfStream extends AsyncTask<String,Void,InputStream> {

        @Override
        protected InputStream doInBackground(String... strings) {
            InputStream inputStream = null;
            try {
                URL url = new URL(strings[0]);
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                if (urlConnection.getResponseCode() == 200) {
                    inputStream = new BufferedInputStream(urlConnection.getInputStream());
                }

            } catch (IOException e) {
                return null;
            }
            return inputStream;
        }

        @Override
        protected void onPostExecute(InputStream inputStream) {
            pdfView.fromStream(inputStream).load();
        }


    }
}

到此kotlin文件

class pdfActivity：AppCompatActivity（）{

lateinit var pdfview: PDFView
lateinit var text1 : TextView
var database:FirebaseDatabase=FirebaseDatabase.getInstance()
var mref :DatabaseReference=database.getReference("url")

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_pdf)

    pdfview=findViewById(R.id.pdfView33)
    text1=findViewById(R.id.text11)

    



}

}

主要问题是这个

class RetrivePdfStream {

解决方法

您可能要在此处修复某些格式。

此外，如果我理解正确，则希望将Java迁移到Kotlin。 对于Kotlin中的RetrivePdfStream，您不是从AsyncTask继承的。 这样做：

class RetrivePdfStream : AsyncTask<String,Void,InputStream>() { ... }