Detailed explanation of the example of Android implementing online preview of office documents

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public class MainActivity extends AppCompatActivity {
 
    private static final int REQ_STORAGE = 1001;
    private WebView webView;
    private TbsReaderView tbsView;
    private FrameLayout container;
    private String remoteDocUrl = "/";
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        (savedInstanceState);
        setContentView(.activity_main);
 
        webView    = findViewById(.web_view);
        tbsView    = findViewById(.tbs_view);
        container  = findViewById(.tbs_container);
 
        findViewById(.btn_web_preview).setOnClickListener(v -> previewWithWeb());
        findViewById(.btn_tbs_preview).setOnClickListener(v -> previewWithTbs());
    }
 
    /** Solution 1: WebView + Office Online */
    private void previewWithWeb() {
        ();
        ();
 
        WebSettings ws = ();
        (true);
        (true);
        (false);
        (true);
 
        String urlEncoded = (remoteDocUrl);
        String previewUrl = "/op/?src=" + urlEncoded;
        (previewUrl);
    }
 
    /** Solution 2: TBS SDK preview, storage permissions are required */
    private void previewWithTbs() {
        ();
        ();
        if ((this,
            .WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            (this,
                new String[]{.WRITE_EXTERNAL_STORAGE}, REQ_STORAGE);
        } else {
            downloadAndOpenWithTbs(remoteDocUrl);
        }
    }
 
    @Override
    public void onRequestPermissionsResult(int req,
        @NonNull String[] perms, @NonNull int[] grantResults) {
        if (req == REQ_STORAGE && >0
            && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            downloadAndOpenWithTbs(remoteDocUrl);
        } else {
            (this, "Storage permission denied", Toast.LENGTH_SHORT).show();
        }
    }
 
    /** After downloading it locally, open it with TbsReaderView */
    private void downloadAndOpenWithTbs(String urlStr) {
        new Thread(() -> {
            try {
                URL url = new URL(urlStr);
                HttpURLConnection conn =
                    (HttpURLConnection) ();
                ();
                InputStream is = ();
                File file = new File(getExternalFilesDir(null), "");
                FileOutputStream fos = new FileOutputStream(file);
                byte[] buf = new byte[4096];
                int len;
                while ((len = (buf))>0) (buf,0,len);
                ();
                ();
 
                runOnUiThread(() -> openFileInTbs(()));
            } catch (Exception e) {
                ();
                runOnUiThread(() ->
                    (this, "Download failed", Toast.LENGTH_SHORT).show());
            }
        }).start();
    }
 
    private void openFileInTbs(String filePath) {
        Bundle params = new Bundle();
        (TbsReaderView.KEY_FILE_PATH, filePath);
        (TbsReaderView.KEY_TEMP_PATH,
            getExternalFilesDir(null).getPath());
        boolean ok = (getFileType(filePath), false);
        if (ok) {
            (params);
        } else {
            (this, "TBS kernel is not loaded or not supported", Toast.LENGTH_SHORT).show();
        }
    }
 
    private String getFileType(String path) {
        if (path == null || !(".")) return "";
        return (('.') + 1);
    }
 
    @Override
    protected void onDestroy() {
        ();
        ();
    }
}

<!--  —— statement INTERNET With read and write permissions，And register TbsReaderView Permissions -->
<manifest xmlns:andro
    package="">
  <uses-permission android:name=""/>
  <uses-permission android:name=".WRITE_EXTERNAL_STORAGE"/>
  <application
      android:allowBackup="true"
      android:label="OfficePreview"
      android:icon="@mipmap/ic_launcher"
      android:theme="@style/">
    <activity android:name=".MainActivity">
      <intent-filter>
        <action android:name=""/>
        <category android:name=""/>
      </intent-filter>
    </activity>
  </application>
</manifest>

​​​​​​​<!-- activity_main.xml —— Also included WebView and TbsReaderView -->
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:andro
    android:layout_width="match_parent"
    android:layout_height="match_parent">
 
  <!-- WebView Method preview -->
  <WebView
      android:
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:visibility="gone"/>
 
  <!-- TBS SDK Method preview -->
  <FrameLayout
      android:
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:visibility="gone">
    <
        android:
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
  </FrameLayout>
 
  <!-- Bottom button -->
  <LinearLayout
      android:layout_gravity="bottom|center_horizontal"
      android:orientation="horizontal"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:padding="16dp">
    <Button
        android:
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Web Preview"/>
    <Button
        android:
        android:layout_marginStart="16dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TBS Preview"/>
  </LinearLayout>
</FrameLayout>