java - 如何保持第二个进程直到完成 Android 中的第一个进程？

Question

我在保持第二个过程直到完成第一个过程时遇到问题。我正在使用 AsyncTask。

我从 MySql 服务器获取数据。有时获取数据需要更多时间，因为我使用了共享服务器。

因此，有时第二个进程在第一个进程之前运行。

这是代码。

这是我的 ListView 代码

 listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        MainItemListNotes invoiceNotes = (MainItemListNotes) parent.getItemAtPosition(position);if (shareactivitycode.equals("Quote"))
        {
            if (invoiceNotes.getItemType().equals("Labels"))
            {
                getLabelQualityID(invoiceNotes.getItemID());

                getLabelPrice(labelQualityID);

                if (labelNoOfColour.equals("0"))
                {
                    double a = Double.parseDouble(lPurchasePrice);
                    double b = Double.parseDouble(lLowRate);
                    double c = Double.parseDouble(lSellRate);

                    double d = Double.parseDouble(labelWidth);
                    double e = Double.parseDouble(labelHeight);

                    Double f = ((d * e) / 625.0000) * a;
                    Double g = Double.parseDouble(String.format("%.4f", f));
                    Log.e("0purchaseP", String.valueOf(g));
                    Log.e("0purchaseP", labelWidth + " * " + labelHeight + " / " + "625" + " * " + lPurchasePrice);

                    Double h = Double.parseDouble(String.format("%.4f", ((d * e) / 625.0000) * b));
                    Log.e("0LowP", String.valueOf(h));
                    Log.e("0LowP", labelWidth + " * " + labelHeight + " / " + "625" + " * " + lLowRate);

                    Double i = Double.parseDouble(String.format("%.4f", ((d * e) / 625.0000) * c));
                    Log.e("0SellP", String.valueOf(i));
                    Log.e("0SellP", labelWidth + " * " + labelHeight + " / " + "625" + " * " + lSellRate);

                    Intent intent = new Intent(ItemList.this, NewQuotation.class);
                    intent.putExtra("itemid", invoiceNotes.getItemID());
                    intent.putExtra("itemname", invoiceNotes.getItemName());
                    intent.putExtra("hsncode", invoiceNotes.getHSNCode());
                    intent.putExtra("itemtype", invoiceNotes.getItemType());
                    intent.putExtra("labelwidth", labelWidth);
                    intent.putExtra("labelheight", labelHeight);
                    intent.putExtra("packing", labelPacking);
                    intent.putExtra("purchaserate", String.valueOf(g));
                    intent.putExtra("lowrate", String.valueOf(h));
                    intent.putExtra("sellrate", String.valueOf(i));
                    setResult(3, intent);
                    finish();
                }
            }
        }
    }
});

这是getLabelQualityID(invoiceNotes.getItemID());代码

private void getLabelQualityID(String itemid) {
    String URL = "myserverurl.com";
    class VoucherDetails extends AsyncTask<Void, Void, String> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);

            try {
                JSONObject obj = new JSONObject(s);

                if (!obj.getBoolean("error")) {

                    JSONObject product = obj.getJSONObject("voucher");

                    labelQualityID = product.getString("id");
                    labelWidth = product.getString("width");
                    labelHeight = product.getString("height");
                    labelNoOfColour = product.getString("noofcolor");
                    labelPacking = product.getString("labelpacking");

                } else {
                    Toast.makeText(getApplicationContext(), "Invalid Voucher ID", Toast.LENGTH_SHORT).show();
                }
            } catch (JSONException e)
            {
                e.printStackTrace();
                Log.e("Sum Error ", e.toString());
                Toast.makeText(getApplicationContext(), "Error : "+e.toString(), Toast.LENGTH_SHORT).show();
            }
        }

        @Override
        protected String doInBackground(Void... voids) {
            RequestHandler requestHandler = new RequestHandler();

            HashMap<String, String> params = new HashMap<>();
            params.put("itemid", itemid);

            return requestHandler.sendPostRequest(URL, params);
        }
    }

    VoucherDetails ul = new VoucherDetails();
    ul.execute();
}

这是getLabelPrice(labelQualityID);代码

private void getLabelPrice(String qualityid) {
    String URL = "myserverurl.com";
    class VoucherDetails extends AsyncTask<Void, Void, String> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);

            try {
                JSONObject obj = new JSONObject(s);

                if (!obj.getBoolean("error")) {

                    JSONObject product = obj.getJSONObject("voucher");

                    lPurchasePrice = product.getString("purchaserate");
                    lLowRate = product.getString("lowrate");
                    lSellRate = product.getString("sellrate");

                } else {
                    Toast.makeText(getApplicationContext(), "Invalid Voucher ID", Toast.LENGTH_SHORT).show();
                }
            } catch (JSONException e)
            {
                e.printStackTrace();
                Log.e("Sum Error ", e.toString());
                Toast.makeText(getApplicationContext(), "Error : "+e.toString(), Toast.LENGTH_SHORT).show();
            }
        }

        @Override
        protected String doInBackground(Void... voids) {
            RequestHandler requestHandler = new RequestHandler();

            HashMap<String, String> params = new HashMap<>();
            params.put("id", qualityid);

            return requestHandler.sendPostRequest(URL, params);
        }
    }

    VoucherDetails ul = new VoucherDetails();
    ul.execute();
}

labelNoOfColour 来自 getLabelQualityID()& lPurchasePrice, lLowRate, lSellRate, labelWidth, labelHeight 来自getLabelPrice() 函数。

有时 getLabelQualityID() 和 getLabelPrice() 需要时间来获取数据。 & if (labelNoOfColour.equals("0"))，进程在获取数据之前执行。

有时 getLabelPrice() 过程在 getLabelQualityID() 完成之前运行。

请指导我如何在第一个过程完成之前保持第二个过程。

Answer 1

当您运行多个 AsycTask 时，一个线程可能先于另一个线程执行，这很常见。因此，为确保顺序处理，您需要为您的 AsyncTask 设置一个监听器，以跟踪线程是否已完成。我想建议以下实现。

创建一个 interface 类，如下所示。

public interface ThreadFinishListener {
    void onThreadFinished();
}

现在为您的第一个线程创建一个监听器变量和一个构造函数，我想这是 VoucherDetails。

private void getLabelQualityID(String itemid) {

    String URL = "myserverurl.com";

    class VoucherDetails extends AsyncTask<Void, Void, String> {

        // Create a listener
        ThreadFinishListener listener;

        // Create a constructor
        public VoucherDetails(ThreadFinishListener listener) {
            this.listener = listener;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);

            try {
                JSONObject obj = new JSONObject(s);

                if (!obj.getBoolean("error")) {

                    JSONObject product = obj.getJSONObject("voucher");

                    labelQualityID = product.getString("id");
                    labelWidth = product.getString("width");
                    labelHeight = product.getString("height");
                    labelNoOfColour = product.getString("noofcolor");
                    labelPacking = product.getString("labelpacking");

                    // invoke the listener method here when you are done with your first thread
                    listener.onThreadFinished();

                } else {
                    Toast.makeText(getApplicationContext(), "Invalid Voucher ID", Toast.LENGTH_SHORT).show();
                }
            } catch (JSONException e) {
                e.printStackTrace();
                Log.e("Sum Error ", e.toString());
                Toast.makeText(getApplicationContext(), "Error : "+e.toString(), Toast.LENGTH_SHORT).show();
            }
        }

        @Override
        protected String doInBackground(Void... voids) {
            RequestHandler requestHandler = new RequestHandler();

            HashMap<String, String> params = new HashMap<>();
            params.put("itemid", itemid);

            return requestHandler.sendPostRequest(URL, params);
        }
    }

    VoucherDetails ul = new VoucherDetails(new ThreadFinishListener() {
        @Override
        public void onThreadFinished() {
            // Call the second thread here
        }
    });

    ul.execute();
}

希望对您有所帮助!