Question

在我的Android应用程序中，我将Launcher活动（称为MainActivity）存储在MainActivity类中的静态变量中; 我正在使用这个静态Activity引用来获取应用程序资源，首选项和其他内容;

但有时，我发现应用程序崩溃了，因为对象引用为null;

是否有任何原因导致对象引用变为NULL？
如何防止这种NullPointerException？

我的代码：

MainActivity：

public class MainActivity extends Activity {
    private static MainActivity sInstance = null;

    public static MainActivity getInstance() {
        return sInstance;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       sInstance = this;
       // other code
   }
}

Helper.java ：

public static int getColor(int resID) {
    return MainActivity.getInstance().getColor(resID);
}

Answer 1

//For this type of issue, please use application class object. If you used Activity class then when //activity destroys then it will become null. So you got the null pointer exception.


public class MyApplication extends Application {
    public static MyApplication myApplication = null;

    @Override
    public void onCreate() {
        // TODO Auto-generated method stub
        super.onCreate();
        myApplication = (MyApplication) getApplicationContext();
    }

    public static MyApplication getInstance() {
        return myApplication;
    }

}

//Your method looks like this
public static int getColor(int resID) {
        return MyApplication.getInstance().getResources().getColor(resID);
    }

My Android Launcher Activity的静态引用变为null

1 个答案: