android - 无法从 Util 类型对非静态方法 getIMEI() 进行静态引用

Question

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    String test =  Util.imei();
}


import android.content.Context;
import android.telephony.TelephonyManager;

public class Util{
    Context context;

    public Util(Context context) {
        this.context = context;
    }

    public String imei() {
        TelephonyManager telephonyManager = (TelephonyManager) context
                .getSystemService(Context.TELEPHONY_SERVICE);
        return telephonyManager.getDeviceId();
    }
}

出现错误“无法从 Util 类型对非静态方法 imei() 进行静态引用”。如果我将行更改为:

public static String imei() {
    ...
    static Context context;

我收到一个错误并使应用程序崩溃。("E/AndroidRuntime(629): Caused by:java.lang.NullPointerException")

Answer 1

两种写法:

第一 非静态

public class Util {
    Context context;

    public Util(Context context) {
        this.context = context;
    }

    public String imei() {
        TelephonyManager telephonyManager = (TelephonyManager) context
                .getSystemService(Context.TELEPHONY_SERVICE);
        return telephonyManager.getDeviceId();
    }
}

然后在onCreate方法中

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Util u = new Util(this);
    String test =  u.imei();
}

第二 静态

public class Util {
    public static String imei(Context context) {
        TelephonyManager telephonyManager = (TelephonyManager) context
                .getSystemService(Context.TELEPHONY_SERVICE);
        return telephonyManager.getDeviceId();
    }
}

然后在onCreate方法中

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    String test =  Util.imei(this);
}