java - AsyncTask - 从主 UI 线程调用

Question

在我为 Android 应用程序中的 Activity 组合的 AsyncTask 期间尝试显示和隐藏对话框时，我遇到了问题。

这是我目前正在做的事情:

public void syncCard(final Tag tag) {
    syncTask = new SyncTask();
    syncTask.execute(tag);
}

private class SyncTask extends AsyncTask<Tag, Void, Void> {
    private final Dialog dialog;
    private boolean mException;

    public SyncTask() {
        // Prepare dialog
        dialog = buildSyncingDialog();
    }

    @Override
    protected void onPreExecute() {
        dialog.show();
    }

    @Override
    protected Void doInBackground(Tag... params) {
        mTagcomm = IsoDep.get(params[0]);
        if (mTagcomm == null) {
            //TODO - Handle communication error with the present card
        }
        mException = false;

        try {
             // Open connection
            mTagcomm.connect();
            lastAts = getAts(mTagcomm);

            mProvider.setmTagCom(mTagcomm);

            EmvParser parser = new EmvParser(mProvider, true);
            mCard = parser.readEmvCard();
            if (mCard != null) {
                mCard.setAtrDescription(extractAtsDescription(lastAts));
            }

        } catch (IOException e) {
            mException = true;
        } finally {
            // close tagcomm
            IOUtils.closeQuietly(mTagcomm);
        }

        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
       if (dialog.isShowing()) {
           dialog.dismiss();
       }

        if (!mException) {
            if (mCard != null) {
                showPaymentCardDetails();
            } else if (mCard.isNfcLocked()) {
                //TODO - Show error message informing user the card is locked
            }
        } else {

        }
    }

    private Dialog buildSyncingDialog() {
        String syncingText = String.format( "%s\n%s",
                getString( R.string.syncing ), getString( R.string.do_not_remove_card ) );
        Dialog dialog = new CustomDialog( PaymentCardRegisterActivity.this,
                syncingText, R.layout.layout_syncing );
        dialog.setCancelable( false );

        return dialog;
    }

    @Override
    public void onCancelled() {
        dialog.dismiss();
    }
}

我看到以下错误:

java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

我遇到了这个旧答案 - Can't create handler inside thread which has not called Looper.prepare()

但是我仍然对我需要做什么感到有点困惑，该帖子的最后一个回复提到从 UI 线程运行任务，我将如何使用上面的代码来执行此操作？

编辑

我的 Activity 类扩展了 NfcActivity，因为我使用此类来读取非接触式卡详细信息。

我的 syncCard 正在从另一个后台线程调用(我相信)，就像这样

@Override
public void onNewIntent(final Intent intent) {
    super.onNewIntent(intent);
    processIntent(intent);
}

private void processIntent(final Intent intent) {
    String action = intent.getAction();

    if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) {
        Tag tagFromIntent = intent.getParcelableExtra( NfcAdapter.EXTRA_TAG );
        onTagDiscovered(tagFromIntent);
    }
}

@Override
public void onTagDiscovered( final Tag tag ) {
    super.onTagDiscovered(tag);
    try {
        PaymentCardRegisterActivity.this.syncCard(tag);
    } catch ( Exception e) {
        Log.e( PaymentCardRegisterActivity.class.getName(), "Failed to sync card", e );
        // Return to start activity
        finish();
    }
}

Answer 1

如果 onTagDiscovered 正在非 UI 线程的线程上运行，那么您应该将对 syncCard 的调用分派(dispatch)到主线程。如果您有对 Activity 的引用，则可以使用 runOnUiThread 并发布 Runnable。这将确保 Runnable 在主线程上执行。在您的代码中，我认为您需要更改此内容

@Override
public void onTagDiscovered( final Tag tag ) {
    super.onTagDiscovered(tag);
    try
    {
            PaymentCardRegisterActivity.this.syncCard(tag);
    }
    catch ( Exception e)
    {
            Log.e( PaymentCardRegisterActivity.class.getName(), "Failed to sync card", e );
            // Return to start activity
            finish();
    }
}

进入此

@Override
public void onTagDiscovered( final Tag tag ) {
    super.onTagDiscovered(tag);
    runOnUiThread(new Runnable() {

        public void run() {
            try {
                PaymentCardRegisterActivity.this.syncCard(tag);
            } catch ( Exception e) {
                Log.e( PaymentCardRegisterActivity.class.getName(), "Failed to sync card", e );
            }
        }
    });
}