0

我的问题与后退按钮和后台堆栈有关，我有一个用于读取 nfc 标签的应用程序，所以我启动了 Activity A，然后转到 Activity B，它在清单中声明为 SingleTop。我将手机靠近标签，它会读取标签，此时一切正常。

如果我按下后退按钮，它将返回到活动 B，而不是转到活动 A，然后如果我再次按下后退按钮，它会转到活动 A。

像这样：

A->B->阅读标签->B->按返回按钮->B->按返回按钮->A->按返回按钮->关闭应用程序。

我想要这样：

A->B->阅读标签->B->按返回按钮-> A->按返回按钮->关闭应用程序。

我只想要 B 的一个实例。我尝试了单个任务，但问题是我点击了应用程序图标，并启动了活动 b，但保留了读取标签的意图。

public class B extends Activity {
private static final String KINVEY_KEY = YOUR_APP_KEY;
private static final String KINVEY_SECRET_KEY = 'YOUR_APP_SECRET_KEY';

private KCSClient kinveyClient;
private NfcAdapter mNfcAdapter;

private Button mEnableWriteButton;
private EditText mTextField;
private ProgressBar mProgressBar;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_tags);

    mTextField = (EditText) findViewById(R.id.text_field);

    mProgressBar = (ProgressBar) findViewById(R.id.progress_bar);
    mProgressBar.setVisibility(View.GONE);

    mEnableWriteButton = (Button) findViewById(R.id.enable_write_button);
    mEnableWriteButton.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            setTagWriteReady(!isWriteReady);
            mProgressBar.setVisibility(isWriteReady ? View.VISIBLE : View.GONE);
        }
    });

    mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
    if (mNfcAdapter == null) {
        Toast.makeText(this, 'Sorry, NFC is not available on this device', Toast.LENGTH_SHORT).show();
        finish();
    }

    // Initialize Kinvey
    KinveySettings settings = new KinveySettings(KINVEY_KEY, KINVEY_SECRET_KEY);
    kinveyClient = KCSClient.getInstance(this.getApplicationContext(), settings);
}

private boolean isWriteReady = false;

public void setTagWriteReady(boolean isWriteReady) {
    this.isWriteReady = isWriteReady;
    if (isWriteReady) {
        IntentFilter[] writeTagFilters = new IntentFilter[] { new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED) };
        mNfcAdapter.enableForegroundDispatch(TagsActivity.this, NfcUtils.getPendingIntent(TagsActivity.this),
                writeTagFilters, null);
    } else {
        // Disable dispatch if not writing tags
        mNfcAdapter.disableForegroundDispatch(TagsActivity.this);
    }
    mProgressBar.setVisibility(isWriteReady ? View.VISIBLE : View.GONE);
}

@Override
public void onNewIntent(Intent intent) {
    // onResume gets called after this to handle the intent
    setIntent(intent);
}

@Override
public void onResume() {
    super.onResume();
    if (isWriteReady && NfcAdapter.ACTION_TAG_DISCOVERED.equals(getIntent().getAction())) {
        processWriteIntent(getIntent());
    } else if (!isWriteReady
            && (NfcAdapter.ACTION_TAG_DISCOVERED.equals(getIntent().getAction()) || NfcAdapter.ACTION_NDEF_DISCOVERED
                    .equals(getIntent().getAction()))) {
        processReadIntent(getIntent());
    }
}

private static final String MIME_TYPE = 'application/com.tapped.nfc.tag';


public void processWriteIntent(Intent intent) {
    if (isWriteReady && NfcAdapter.ACTION_TAG_DISCOVERED.equals(getIntent().getAction())) {

        Tag detectedTag = getIntent().getParcelableExtra(NfcAdapter.EXTRA_TAG);

        String tagWriteMessage = mTextField.getText().toString();
        byte[] payload = new String(tagWriteMessage).getBytes();

        if (detectedTag != null && NfcUtils.writeTag(
                NfcUtils.createMessage(MIME_TYPE, payload), detectedTag)) {

            Toast.makeText(this, "Wrote '" + tagWriteMessage + "' to a tag!", 
                    Toast.LENGTH_LONG).show();
            setTagWriteReady(false);
        } else {
            Toast.makeText(this, "Write failed. Please try again.", Toast.LENGTH_LONG).show();
        }
    }
}

public void processReadIntent(Intent intent) {
    List<NdefMessage> intentMessages = NfcUtils.getMessagesFromIntent(intent);
    List<String> payloadStrings = new ArrayList<String>(intentMessages.size());

    for (NdefMessage message : intentMessages) {
        for (NdefRecord record : message.getRecords()) {
            byte[] payload = record.getPayload();
            String payloadString = new String(payload);

            if (!TextUtils.isEmpty(payloadString))
                payloadStrings.add(payloadString);
        }
    }

    if (!payloadStrings.isEmpty()) {
        String content =  TextUtils.join(",", payloadStrings);
        Toast.makeText(TagsActivity.this, "Read from tag: " + content,
                Toast.LENGTH_LONG).show();
        saveTag(content);
    }
}

private void saveTag(String tagMessage){
    TagReadEntity tag = new TagReadEntity(UUID.randomUUID().toString(), 
            tagMessage, System.currentTimeMillis());

    kinveyClient.mappeddata("tags").save(tag, new ScalarCallback<TagReadEntity>() {

        @Override
        public void onSuccess(TagReadEntity tag) {
            Log.i("NFC Demo", "Saved tag!");
        }

        @Override
        public void onFailure(Throwable e) {
            Log.e("NFC Demo", "Error saving tag", e);
        }
    });
}
}

和清单：

<activity
        android:name=".TagsActivity"
        android:label="@string/title_activity_tags"
        android:launchMode="singleTop"
        android:screenOrientation="portrait" >
        <intent-filter>
            <action android:name="android.nfc.action.NDEF_DISCOVERED" />

            <category android:name="android.intent.category.DEFAULT" />

            <data android:mimeType="application/com.tapped.nfc.tag" />
        </intent-filter>
        <intent-filter>
            <action android:name="android.nfc.action.TAG_DISCOVERED" />

            <category android:name="android.intent.category.DEFAULT" />

            <data android:mimeType="application/com.tapped.nfc.tag" />
        </intent-filter>
    </activity>
4

1 回答 1

0

我将任务声明为单任务，现在似乎可以工作了。

android:launchMode="singleTask"

我尝试了标准，每次我读取一个 nfc 标签时，都会创建一个新活动，如果读取 10 个标签，我需要按 9 次后退按钮。在我尝试过 singleTop 之后，现在我从 A 到 B，然后无论我阅读标签多少次，只有 2 个 B 实例，所以我需要按一次返回到活动 B，然后再返回到关闭应用程序。

于 2013-01-22T02:04:32.600 回答