Android工作室 - 不产生输出

Question

我想创建一个可以扫描连接到我的Lan网络的其他IP的应用程序。这是我的java代码，也许有一个错误导致我的编码没有产生结果。

package com.example.admin.ipscanner3;

import android.content.Context;
import android.net.wifi.WifiManager;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

TextView tvWifiState;
TextView tvScanning, tvResult;

ArrayList<InetAddress> inetAddresses;

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

    tvWifiState = (TextView)findViewById(R.id.WifiState);
    tvScanning = (TextView)findViewById(R.id.Scanning);
    tvResult = (TextView)findViewById(R.id.Result);

    //To prevent memory leaks on devices prior to Android N,
    //retrieve WifiManager with
    //getApplicationContext().getSystemService(Context.WIFI_SERVICE),
    //instead of getSystemService(Context.WIFI_SERVICE)
    WifiManager wifiManager =
            (WifiManager) 
 getApplicationContext().getSystemService(Context.WIFI_SERVICE);
    tvWifiState.setText(readtvWifiState(wifiManager));

    new ScanTask(tvScanning, tvResult).execute();
    }

    // "android.permission.ACCESS_WIFI_STATE" is needed
    private String readtvWifiState(WifiManager wm){
    String result = "";
    switch (wm.getWifiState()){
        case WifiManager.WIFI_STATE_DISABLED:
            result = "WIFI_STATE_DISABLED";
            break;
        case WifiManager.WIFI_STATE_DISABLING:
            result = "WIFI_STATE_DISABLING";
            break;
        case WifiManager.WIFI_STATE_ENABLED:
            result = "WIFI_STATE_ENABLED";
            break;
        case WifiManager.WIFI_STATE_ENABLING:
            result = "WIFI_STATE_ENABLING";
            break;
        case WifiManager.WIFI_STATE_UNKNOWN:
            result = "WIFI_STATE_UNKNOWN";
            break;
        default:
    }
    return result;
   }

    private class ScanTask extends AsyncTask<Void, String, Void> {

    TextView tvCurrentScanning, tvScanResullt;
    ArrayList<String> canonicalHostNames;

    public ScanTask(TextView tvCurrentScanning, TextView tvScanResullt) {
        this.tvCurrentScanning = tvCurrentScanning;
        this.tvScanResullt = tvScanResullt;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        tvCurrentScanning.setText("Finished.");
        tvScanResullt.setText("");
        for(int i = 0; i < inetAddresses.size(); i++){
            tvScanResullt.append(canonicalHostNames.get(i) + "\n");
        }
    }

    @Override
    protected Void doInBackground(Void... voids) {
        scanInetAddresses();
        return null;
    }

    @Override
    protected void onProgressUpdate(String... values) {
        tvCurrentScanning.setText(values[0]);
    }

    private void scanInetAddresses(){
        //May be you have to adjust the timeout
        final int timeout = 500;

        if(inetAddresses == null){
            inetAddresses = new ArrayList<>();
        }
        inetAddresses.clear();

        if(canonicalHostNames == null){
            canonicalHostNames = new ArrayList<>();
        }
        canonicalHostNames.clear();

        //For demonstration, scan 192.168.1.xxx only
        byte[] ip = {(byte) 183, (byte) 171, (byte) 93, 0};
        for (int j = 0; j < 255; j++) {
            ip[3] = (byte) j;
            try {
                InetAddress checkAddress = InetAddress.getByAddress(ip);
                publishProgress(checkAddress.getCanonicalHostName());
                if (checkAddress.isReachable(timeout)) {
                    inetAddresses.add(checkAddress);

 canonicalHostNames.add(checkAddress.getCanonicalHostName());
                }
            } catch (UnknownHostException e) {
                e.printStackTrace();
                publishProgress(e.getMessage());
            } catch (IOException e) {
                e.printStackTrace();
                publishProgress(e.getMessage());
            }
        }
      }
    }
  }

这是我的界面/布局。我认为这里没有错误。

    <?xml version="1.0" encoding="utf-8"?>
  <android.support.constraint.ConstraintLayout 
 xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context="com.example.admin.ipscanner3.MainActivity">

   <TextView
      android:id="@+id/title"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="center_horizontal"
      android:layout_marginBottom="8dp"
      android:layout_marginEnd="8dp"
      android:layout_marginTop="8dp"
      android:autoLink="web"
      android:text="http://android-er.blogspot.com/"
      android:textStyle="bold"
      app:layout_constraintBottom_toBottomOf="parent"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintHorizontal_bias="0.502"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toTopOf="parent"
      app:layout_constraintVertical_bias="0.069" />

  <TextView
      android:id="@+id/WifiState"
      android:layout_width="match_parent"
      android:layout_height="wrap_content" />

  <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:orientation="horizontal"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.144">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Scanning: " />

    <TextView
        android:id="@+id/Scanning"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textStyle="italic" />
  </LinearLayout>

  <TextView
    android:id="@+id/Result"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:textStyle="bold"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.212" />

   </android.support.constraint.ConstraintLayout>

我已经添加了这两个权限，以获得访问wifi状态和互联网的权限。

    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
    <uses-permission android:name="android.permission.INTERNET"/>