Question

以下代码片段是用于反应原生的NFC模块。我用它读了NFC标签ID。问题是如果你把应用程序放在后台，如果你再次点击应用程序图标，应用程序将崩溃，但如果你从任务列表中打开它，它可以正常工作。

NFC读取模块：

＆＃13;

//package com.toastexample;
package net.opencampus.android.client;
import android.widget.Toast;
import android.util.Log;

import com.facebook.react.bridge.NativeModule;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.bridge.ReactContext;
import com.facebook.react.bridge.ReactContextBaseJavaModule;
import com.facebook.react.bridge.ReactMethod;
import com.facebook.react.bridge.ActivityEventListener;
import com.facebook.react.bridge.LifecycleEventListener;

import android.app.Activity;
import android.content.Intent;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import java.nio.ByteBuffer;
import com.facebook.react.bridge.WritableMap;
import com.facebook.react.bridge.Arguments;
import com.facebook.react.bridge.Promise;
import com.facebook.react.modules.core.DeviceEventManagerModule;
import android.support.annotation.Nullable;

import java.util.Map;
import java.util.HashMap;

public class NfcReadModule extends ReactContextBaseJavaModule implements ActivityEventListener, LifecycleEventListener {
public static final String TAG = "NFCActivity";
  private static final String DURATION_SHORT_KEY = "SHORT";
  private static final String DURATION_LONG_KEY = "LONG";

  private ReactApplicationContext reactContext;

  private static final char[] HAX_ARRAY = "0123456789ABCDEF".toCharArray();
  String serialNumber;
  String intentText = "Empty";
  Promise tagPromise;

  public NfcReadModule(ReactApplicationContext reactContext) {
    super(reactContext);
    this.reactContext = reactContext;
    this.reactContext.addActivityEventListener(this);
  }

  @Override
  public String getName() {
    return "NfcReadModule";
  }

  @Override
  public void onNewIntent(Intent intent) {
    intentText = "onNewIntent";
    Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
    serialNumber = bytesToHex(tag.getId());
    WritableMap params = Arguments.createMap();
    params.putString("serial", serialNumber);
    sendEvent(this.reactContext, "tagDetected", params);

  }

  @ReactMethod
  public void getCardId(Promise promise) {
    this.tagPromise = promise;
  }

  @Override
  public void onHostResume() {
    
  }

  @Override
  public void onHostPause() {
    
  }

  @Override
  public void onHostDestroy() {
    
  }

  @Override
    public void onActivityResult(
      final Activity activity,
      final int requestCode,
      final int resultCode,
      final Intent intent) {

    }

  @ReactMethod
  public void show() {

  }

  @Override
  public Map<String, Object> getConstants() {
    final Map<String, Object> constants = new HashMap<>();
    constants.put(DURATION_SHORT_KEY, Toast.LENGTH_SHORT);
    constants.put(DURATION_LONG_KEY, Toast.LENGTH_LONG);
    return constants;
  }

  private static String bytesToHex(byte[] bytes) {
    char[] hexChars = new char[bytes.length * 2];
    for ( int j = 0; j < bytes.length; j++ ) {
        int v = bytes[bytes.length - j - 1] & 0xFF;
        hexChars[j * 2] = HAX_ARRAY[v >>> 4];
        hexChars[j * 2 + 1] = HAX_ARRAY[v & 0x0F];
    }
    return new String(hexChars);
  }

  private void sendEvent(ReactContext reactContext, String eventName, @Nullable WritableMap params) {
    if (reactContext.hasActiveCatalystInstance()) {
      reactContext
        .getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)
        .emit(eventName, params);
    }
  }
}

＆＃13;

崩溃时从logcat登录：

＆＃13;

05-09 10:34:03.457 22282 22282 E AndroidRuntime: FATAL EXCEPTION: main
05-09 10:34:03.457 22282 22282 E AndroidRuntime: Process: net.xxxx.android.client, PID: 22282
05-09 10:34:03.457 22282 22282 E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'byte[] android.nfc.Tag.getId()' on a null object reference
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at net.xxxx.android.client.NfcReadModule.onNewIntent(NfcReadModule.java:61)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at com.facebook.react.bridge.ReactContext.onNewIntent(ReactContext.java:208)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at com.facebook.react.ReactInstanceManager.onNewIntent(ReactInstanceManager.java:503)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at com.facebook.react.ReactActivityDelegate.onNewIntent(ReactActivityDelegate.java:189)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at com.facebook.react.ReactActivity.onNewIntent(ReactActivity.java:99)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.app.Instrumentation.callActivityOnNewIntent(Instrumentation.java:1223)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.app.Instrumentation.callActivityOnNewIntent(Instrumentation.java:1235)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.app.ActivityThread.deliverNewIntents(ActivityThread.java:2802)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.app.ActivityThread.performNewIntents(ActivityThread.java:2817)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.app.ActivityThread.handleNewIntent(ActivityThread.java:2833)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.app.ActivityThread.-wrap15(ActivityThread.java)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1556)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.os.Handler.dispatchMessage(Handler.java:102)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.os.Looper.loop(Looper.java:154)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at android.app.ActivityThread.main(ActivityThread.java:6119)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at java.lang.reflect.Method.invoke(Native Method)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
05-09 10:34:03.457 22282 22282 E AndroidRuntime: 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
05-09 10:34:03.467   607  2381 W ActivityManager:   Force finishing activity net.xxxx.android.client/.MainActivity

＆＃13;

我做错了什么？提前谢谢。

Answer 1

通过添加检查标记是否为空来修复：

@Override
  public void onNewIntent(Intent intent) {
    intentText = "onNewIntent";
    Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
    if (tag != null) {
      serialNumber = bytesToHex(tag.getId());
      WritableMap params = Arguments.createMap();
      params.putString("serial", serialNumber);
      sendEvent(this.reactContext, "tagDetected", params);
    }
  }

React Native：Android应用程序崩溃，onNewIntent

1 个答案: