android studio中货币转换计算器

以下是一个简单的货币转换计算器的示例代码，使用了汇率API进行货币转换：

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    EditText editTextAmount;
    TextView textViewResult;

    String currencyFrom = "USD";
    String currencyTo = "CNY";
    double rate = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        editTextAmount = findViewById(R.id.editTextAmount);
        textViewResult = findViewById(R.id.textViewResult);

        // 获取汇率
        new GetRateTask().execute();
    }

    public void onClickConvert(View view) {
        // 获取输入金额
        String input = editTextAmount.getText().toString().trim();
        if (input.isEmpty()) {
            Toast.makeText(this, "请输入金额", Toast.LENGTH_SHORT).show();
            return;
        }

        // 计算转换结果
        double amount = Double.parseDouble(input);
        double result = amount * rate;

        // 显示转换结果
        textViewResult.setText(String.format("%.2f %s = %.2f %s", amount, currencyFrom, result, currencyTo));
    }

    private class GetRateTask extends AsyncTask<Void, Void, String> {

        @Override
        protected String doInBackground(Void... voids) {
            try {
                URL url = new URL("https://api.exchangeratesapi.io/latest?base=" + currencyFrom + "&symbols=" + currencyTo);
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.setRequestMethod("GET");
                connection.setConnectTimeout(5000);
                connection.setReadTimeout(5000);

                BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String line;
                StringBuilder response = new StringBuilder();
                while ((line = reader.readLine()) != null) {
                    response.append(line);
                }
                reader.close();

                return response.toString();
            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }
        }

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

            if (s != null) {
                try {
                    JSONObject jsonObject = new JSONObject(s);
                    rate = jsonObject.getJSONObject("rates").getDouble(currencyTo);
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

注意：这里使用了第三方API获取汇率，需要在`AndroidManifest.xml`文件中添加网络权限：

<uses-permission android:name="android.permission.INTERNET" />