如何使用android调用api，并写出代码

使用Android调用API需要以下步骤：

1. 在AndroidManifest.xml文件中添加网络权限：

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

2. 在Activity或Fragment中创建一个异步任务（AsyncTask）来执行API调用。在这个异步任务中，可以使用HttpURLConnection或OkHttp等库来发送HTTP请求并获取API响应。

3. 在异步任务的doInBackground()方法中执行API调用，例如：

URL url = new URL("https://api.example.com/data");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");

InputStream in = new BufferedInputStream(conn.getInputStream());
String response = convertStreamToString(in);

其中，convertStreamToString()是将输入流转换为字符串的自定义方法，例如：

private String convertStreamToString(InputStream is) {
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    StringBuilder sb = new StringBuilder();

    String line;
    try {
        while ((line = reader.readLine()) != null) {
            sb.append(line).append('\n');
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    return sb.toString();
}

4. 在异步任务的onPostExecute()方法中处理API响应，例如：

protected void onPostExecute(String response) {
    try {
        JSONObject json = new JSONObject(response);
        JSONArray data = json.getJSONArray("data");

        for (int i = 0; i < data.length(); i++) {
            JSONObject item = data.getJSONObject(i);
            // TODO: 处理API响应数据
        }
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

完整的示例代码如下：

public class MyActivity extends AppCompatActivity {

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

        new ApiTask().execute();
    }

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

        @Override
        protected String doInBackground(Void... voids) {
            try {
                URL url = new URL("https://api.example.com/data");
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");

                InputStream in = new BufferedInputStream(conn.getInputStream());
                String response = convertStreamToString(in);

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

        @Override
        protected void onPostExecute(String response) {
            try {
                JSONObject json = new JSONObject(response);
                JSONArray data = json.getJSONArray("data");

                for (int i = 0; i < data.length(); i++) {
                    JSONObject item = data.getJSONObject(i);
                    // TODO: 处理API响应数据
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }

        private String convertStreamToString(InputStream is) {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            StringBuilder sb = new StringBuilder();

            String line;
            try {
                while ((line = reader.readLine()) != null) {
                    sb.append(line).append('\n');
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            return sb.toString();
        }
    }
}