Question

我正在编写将使用WiFi Aware来发布服务的应用程序，但是我无法通过验证设备是否支持该服务的初始步骤。 API（来自Google，这里为https://developer.android.com/guide/topics/connectivity/wifi-aware）指定使用以下代码行：

context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_WIFI_AWARE);

但是，由于我还没有实例化一个称为“ context”的对象，所以不能将其放入MainActivity类。我试图四处寻找答案，但没有找到任何有效的方法。任何形式的帮助将不胜感激。谢谢。

更新

似乎可以单独使用该方法，但是除非在某个方法（例如我的Publish()方法）中调用它，否则它将导致该应用崩溃。我在下面附加了我的代码以供参考。谢谢。

我的代码：

package com.patrickutz.wifiawarepublish;

import android.content.Context;
import android.content.pm.PackageManager;
import android.net.wifi.aware.AttachCallback;
import android.net.wifi.aware.WifiAwareManager;
import android.net.wifi.aware.WifiAwareSession;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.net.wifi.aware.PublishConfig;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;


public class MainActivity extends AppCompatActivity {

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

// Constant values of WifiAwareManager
String state_change = WifiAwareManager.ACTION_WIFI_AWARE_STATE_CHANGED;
int data_init = WifiAwareManager.WIFI_AWARE_DATA_PATH_ROLE_INITIATOR;
int data_resp = WifiAwareManager.WIFI_AWARE_DATA_PATH_ROLE_RESPONDER;

public void publish(View view) {

    // Check whether or not device supports WiFi Aware
    boolean hasWiFiAware = getPackageManager().hasSystemFeature(PackageManager.FEATURE_WIFI_AWARE);

    // Toast myToast = Toast.makeText(this, message, duration);
    // Messages for whether or not device has WiFi Aware
    Toast hasAware = Toast.makeText(this, "WiFi Aware Supported", Toast.LENGTH_SHORT);
    Toast noAware = Toast.makeText(this, "WiFi Aware Unsupported", Toast.LENGTH_SHORT);

    if (hasWiFiAware) {
        hasAware.show();
    } else {
        noAware.show();
    }

    System.out.println(hasWiFiAware);

    // Create WiFiAwareManager object
    WifiAwareManager wifiAwareManager = (WifiAwareManager)getSystemService(Context.WIFI_AWARE_SERVICE);

    // Check if WiFi Aware is available
    boolean awareAvailable = wifiAwareManager.isAvailable();

    // Messages for whether or not WiFi Aware is available
    Toast isAvailable = Toast.makeText(this, "WiFi Aware Supported", Toast.LENGTH_SHORT);
    Toast notAvailable = Toast.makeText(this, "WiFi Aware Unsupported", Toast.LENGTH_SHORT);

    if (awareAvailable) {
        isAvailable.show();
    } else {
        notAvailable.show();
    }

//        AttachCallback attachCallback = new AttachCallback();
//        Handler handler = new Handler();
//
//        wifiAwareManager.attach(attachCallback, handler);


//        private static final String AWARE_FILE_SHARE_SERVICE_NAME = "Test Publish";
//        PublishConfig config = new PublishConfig.Builder()
//                .setServiceName(AWARE_FILE_SHARE_SERVICE_NAME)
//                .build();


    // Get the text views
    TextView showStateChangeTextView = (TextView) findViewById(R.id.stateChangeTextView);
    TextView showDataPathRoleInitTextView = (TextView) findViewById(R.id.dataPathRoleInitTextView);
    TextView showDataPathRoleRespTextView = (TextView) findViewById(R.id.dataPathRoleRespTextView);

    // Display the new values of current state in the text view.
    showStateChangeTextView.setText("State: " + state_change);
    showDataPathRoleInitTextView.setText("Data Initiator: " + Integer.toString(data_init));
    showDataPathRoleRespTextView.setText("Data Responder: " + Integer.toString(data_resp));

  }
}

Answer 1

您不必初始化Context对象。层次结构中的活动是Context的子类。

您可以在getPackageManager().hasSystemFeature(PackageManager.FEATURE_WIFI_AWARE);类中简单地调用Activity。不必显式初始化Context

Answer 2

看到此Google教程，我正在寻找一种简单的方法来向我们展示调用此方法必须使用context。然后，在activity内，实例化此变量是不必要的，因为她已经存在，因此，只需调用getPackageManager()...

在Android Studio中使用上下文调用PackageManager

2 个答案: