在类中为其他活动调用上下文

Question

我正在检查课程中的SEND_SMS权限：

public class SendSms extends Activity{
    int requestPerm;

    private void checkPermissionSms(){
        if(ContextCompat.checkSelfPermission(, Manifest.permission.SEND_SMS)
                != PackageManager.PERMISSION_GRANTED){
                   ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.SEND_SMS},
                          requestPerm);                                 //If we don't have the permission, request it here
        }
    }

但是在checkSelPermission上，它需要一个上下文，但是我不确定它需要什么上下文（甚至不太确定checkSelfPermission的上下文），我正在关注：

https://developer.android.com/training/permissions/requesting.html#java

上面的方法这样调用：

public static void sendSms(String message){
   // Intent calledSendSMS = getIntent();
    //String message = calledSendSMS.getStringExtra(Intent.EXTRA_TEXT);
 //   PendingIntent pi = PendingIntent.getActivity(this,0, new Intent(this,SendSms.class),0);
    SendSms checkPerm = new SendSms();
    SmsManager sendTheMessage = SmsManager.getDefault();
    String phoneNumber = "5556";
    checkPerm.checkPermissionSms();
    sendTheMessage.sendTextMessage(phoneNumber, null,message,null,null);
}

这个方法是从另一个活动中调用的。 我确实输入了“ this”，但随后出现以下错误：

 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.Context.checkPermission(java.lang.String, int, int)' on a null object reference
                      at android.content.ContextWrapper.checkPermission(ContextWrapper.java:724)
                      at android.support.v4.content.ContextCompat.checkSelfPermission(ContextCompat.java:430)
                      at com.example.android.footysortit.SendSms.checkPermissionSms(SendSms.java:17)

实际上，我要做的就是检查权限，并在需要时请求它。

编辑：如果我在实际活动中添加检查权限，并使用“此”，则工作正常。 那么我如何获得它来传递活动数据呢？

Answer 1

更改此：

SendSms checkPerm = new SendSms();

至：

SendSms checkPerm = new SendSms(this);

SendSms类-您需要创建该类的构造函数

public class SendSms extends Activity {

private Activity mActivity;
private int requestPerm;

public SendSms(Activity mActivity) {
    this.mActivity = mActivity;

}

private void checkPermissionSms() {
    if (ContextCompat.checkSelfPermission(mActivity, Manifest.permission.SEND_SMS) != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.SEND_SMS}, requestPerm);
        //If we don't have the permission, request it here
    }
  }
}