NFC标签阅读器无法在另一个班级启动？

Question

我写了一个程序来读取nfc标签，并将它们可视化到Toast上，这非常好。代码:

package com.example.myapplication;
import android.app.Activity;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.nfc.NdefMessage;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.os.Bundle;
import android.os.Parcelable;
import android.util.Log;
import android.widget.Toast;
import java.io.UnsupportedEncodingException;
public class MainActivity extends Activity {
NfcAdapter nfcAdapter;
PendingIntent pendingIntent;
IntentFilter writeTagFilters[];
Tag myTag;
Context context;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
context = this;


nfcAdapter = NfcAdapter.getDefaultAdapter(this);
if (nfcAdapter == null) {
// Stop here, we definitely need NFC
Toast.makeText(this, "This device doesn't support NFC.", Toast.LENGTH_LONG).show();
finish();
}
readFromIntent(getIntent());
pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
tagDetected.addCategory(Intent.CATEGORY_DEFAULT);
writeTagFilters = new IntentFilter[]{tagDetected};
}
private void readFromIntent(Intent intent) {
String action = intent.getAction();
if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(action)
|| NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)
|| NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {
Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
NdefMessage[] msgs = null;
if (rawMsgs != null) {
msgs = new NdefMessage[rawMsgs.length];
for (int i = 0; i < rawMsgs.length; i++) {
msgs[i] = (NdefMessage) rawMsgs[i];
}
}
buildTagViews(msgs);
}
}
private void buildTagViews(NdefMessage[] msgs) {
if (msgs == null || msgs.length == 0) return;
String text = "";
//        String tagId = new String(msgs[0].getRecords()[0].getType());
byte[] payload = msgs[0].getRecords()[0].getPayload();
String textEncoding = ((payload[0] & 128) == 0) ? "UTF-8" : "UTF-16"; // Get the Text Encoding
int languageCodeLength = payload[0] & 0063; // Get the Language Code, e.g. "en"
// String languageCode = new String(payload, 1, languageCodeLength, "US-ASCII");
try {
// Get the Text
text = new String(payload, languageCodeLength + 1, payload.length - languageCodeLength - 1, textEncoding);
} catch (UnsupportedEncodingException e) {
Log.e("UnsupportedEncoding", e.toString());
}
Toast.makeText(getApplicationContext(), text, Toast.LENGTH_LONG).show();
}


@Override
protected void onNewIntent(Intent intent) {
setIntent(intent);
readFromIntent(intent);
if(NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction())){
myTag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
}
}
}

但是当我想要这个在另一个文件中启动时，应用程序只是崩溃而没有给我一个错误。

这是我使用的代码:

package com.example.myapplication;
import android.app.Activity;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.nfc.NdefMessage;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.os.Bundle;
import android.os.Parcelable;
import android.util.Log;
import android.widget.Toast;
import java.io.UnsupportedEncodingException;
public class MainActivity extends Activity {

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Nfc nfc = new Nfc();
nfc.startnfc();
}
}

我没有改变onCreate，因为它是从我的主应用程序导入的，所以你有一个更容易理解我的代码。这显然不会有什么不同。

package com.example.myapplication;
import static java.sql.DriverManager.println;
import android.app.Activity;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.nfc.NdefMessage;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.os.Bundle;
import android.os.Parcelable;
import android.util.Log;
import android.widget.Toast;
import java.io.UnsupportedEncodingException;
public class Nfc extends Activity {
NfcAdapter nfcAdapter;
PendingIntent pendingIntent;
IntentFilter writeTagFilters[];
Tag myTag;
Context context;

public void startnfc() {
setContentView(R.layout.activity_main);
context = this;


nfcAdapter = NfcAdapter.getDefaultAdapter(this);
if (nfcAdapter == null) {
// Stop here, we definitely need NFC
Toast.makeText(this, "This device doesn't support NFC.", Toast.LENGTH_LONG).show();
finish();
}
readFromIntent(getIntent());
pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
tagDetected.addCategory(Intent.CATEGORY_DEFAULT);
writeTagFilters = new IntentFilter[]{tagDetected};
}
private void readFromIntent(Intent intent) {
String action = intent.getAction();
if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(action)
|| NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)
|| NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {
Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
NdefMessage[] msgs = null;
if (rawMsgs != null) {
msgs = new NdefMessage[rawMsgs.length];
for (int i = 0; i < rawMsgs.length; i++) {
msgs[i] = (NdefMessage) rawMsgs[i];
}
}
buildTagViews(msgs);
}
}
private void buildTagViews(NdefMessage[] msgs) {
if (msgs == null || msgs.length == 0) return;
String text = "";
//        String tagId = new String(msgs[0].getRecords()[0].getType());
byte[] payload = msgs[0].getRecords()[0].getPayload();
String textEncoding = ((payload[0] & 128) == 0) ? "UTF-8" : "UTF-16"; // Get the Text Encoding
int languageCodeLength = payload[0] & 0063; // Get the Language Code, e.g. "en"
// String languageCode = new String(payload, 1, languageCodeLength, "US-ASCII");
try {
// Get the Text
text = new String(payload, languageCodeLength + 1, payload.length - languageCodeLength - 1, textEncoding);
} catch (UnsupportedEncodingException e) {
Log.e("UnsupportedEncoding", e.toString());
}
Toast.makeText(getApplicationContext(), text, Toast.LENGTH_LONG).show();
}


@Override
protected void onNewIntent(Intent intent) {
setIntent(intent);
readFromIntent(intent);
if(NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction())){
myTag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
}
}
}

这是我用Java编程的第二周了。为愚蠢的错误提前道歉

Answer 1

这是一个标准的类继承问题

它看起来就像你试图通过扩展Activity创建一个新的基类

在MainActivity.java中改变

一行public class MainActivity extends Activity {

public class MainActivity extends Nfc {

那么你可以修改

Nfc nfc = new Nfc();
nfc.startnfc();

startnfc()

因为你的Nfc类已经扩展了Activity类，所以当Android框架创建一个MainActivity的实例时，你的startnfc方法是可用的

Activity或从它扩展的东西不是你自己创建的实例