getPackageManager（）正在获取NullPointer异常

Question

我从mainactivity将上下文传递给AppInfo类，然后使用它尝试从AppInfo类访问packagemanager，但是我得到空指针异常。

MainActivity类：

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener{

    Context mContext;

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

AppInfo类：

public class AppInfo  {

    Context mContext;

    AppInfo(Context context)
    {
        this.mContext = context;
    }

    PackageManager pm = mContext.getPackageManager();

日志：

致命的例外：主要

处理：com.example.zahidhasan.myapplication，PID：12255                                                                                   java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.zahidhasan.myapplication / com.example.zahidhasan.uninstaller.MainActivity}：java.lang.NullPointerException：尝试调用虚方法＆＃39; android.content。 pm.PackageManager android.content.Context.getPackageManager（）＆＃39;在null对象引用上                                                                                       在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2298）