这些静态 getter 和 setter 方法有什么问题 - Android？

Question

我对 Android 代码中的一个非常小的问题感到困惑。我在自定义 class（即 'ResultsRoomInfoCustRLYT'）中创建的所有 getter 和 setter 都给我以下 'Java NullPointerException':

05-31 13:37:13.222  29262-29262/com.whitsoft.stan E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
        at com.whitsoft.stan.mods.ResultsRoomInfoCustRLYT.setSingleRoomsNumberTextValue(ResultsRoomInfoCustRLYT.java:61)
        at com.whitsoft.stan.utils.DataFixer.updateRelevantViewsWithSelectedData(DataFixer.java:48)
        at com.whitsoft.stan.mods.StanListFragment.checkIfTheListAdapterDataHasChanged(StanListFragment.java:98)
        at com.whitsoft.stan.mods.StanListFragment.onActivityCreated(StanListFragment.java:49)
        at android.app.Fragment.performActivityCreated(Fragment.java:1707)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:921)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1075)
        at android.app.BackStackRecord.run(BackStackRecord.java:682)
        at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1455)
        at android.app.FragmentManagerImpl.run(FragmentManager.java:441)
        at android.os.Handler.handleCallback(Handler.java:730)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5493)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025)
        at dalvik.system.NativeStart.main(Native Method)

这是实现 getter 和 setter 的自定义 class ('ResultsRoomInfoCustRLYT')：

public class ResultsRoomInfoCustRLYT extends RelativeLayout {

LayoutInflater stanInflater;
private static TextView singleRoomsNumberTV, singleRoomsDescTV, vipRoomsNumberTV, vipRoomsDescTV;

public ResultsRoomInfoCustRLYT(Context context) {
    super(context);

    stanInflater = LayoutInflater.from(context);
    initializeAndLayoutChildren();
}

public ResultsRoomInfoCustRLYT(Context context, AttributeSet attrs) {
    super(context, attrs);

    stanInflater = LayoutInflater.from(context);
    initializeAndLayoutChildren();
}

public ResultsRoomInfoCustRLYT(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);

    stanInflater = LayoutInflater.from(context);
    initializeAndLayoutChildren();
}

private void initializeAndLayoutChildren() {

    stanInflater.inflate(R.layout.cust_rlyt_results_room_info, this, true);

    singleRoomsNumberTV = (TextView) findViewById(R.id.stan_Single_Rooms_Number_TV);
    singleRoomsDescTV = (TextView) findViewById(R.id.stan_Single_Rooms_Description_TV);
    vipRoomsNumberTV = (TextView) findViewById(R.id.stan_VIP_Rooms_Number_TV);
    vipRoomsDescTV = (TextView) findViewById(R.id.stan_VIP_Rooms_Description_TV);
}

public static String getSingleRoomsNumberTextValue() {
    return singleRoomsNumberTV.getText().toString();
}

public static void setSingleRoomsNumberTextValue(String singleRoomsNumberText) {
    singleRoomsNumberTV.setText(singleRoomsNumberText);
} 

public static void setVipRoomsNumberTextValue (String vipRoomsNumberText) {
    vipRoomsNumberTV.setText(vipRoomsNumberText);
}

public static String getVipRoomsDescTextValue () {
    return vipRoomsDescTV.getText().toString();
}

public static void setVipRoomsDescTextValue (String vipRoomsDescText) {
    vipRoomsDescTV.setText(vipRoomsDescText);
}  }

...如您所见，我喜欢使用静态 getter 和 setter，因为它使我可以使用一行代码轻松访问所需的视图。关于我在运行时遇到的这个错误，真正奇怪的是我还有另外两个 classes 使用完全相同的设置 - 并且那些 classes 工作正常（根据需要更新数据).但是，当使用以下调用调用此 class 的设置器时，它们都无法执行：

ResultsRoomInfoCustRLYT.setSingleRoomsNumberTextValue(singleRoomsNumberInfo);
    ResultsRoomInfoCustRLYT.setSingleRoomsDescTextValue(singleRoomsDescInfo);
    ResultsRoomInfoCustRLYT.setVipRoomsNumberTextValue(vipRoomsNumberInfo);
    ResultsRoomInfoCustRLYT.setVipRoomsDescTextValue(vipRoomsDescInfo);

任何帮助将不胜感激。谢谢。肖尔-T.

Answer 1

您的静态 getter 和 setter 访问由非静态方法初始化的静态引用 - initializeAndLayoutChildren。当您在非静态方法中初始化静态变量时，您运行有在初始化之前访问静态变量的风险。您还运行多次初始化静态变量的风险 - 每次创建新实例时。

例如，静态方法setSingleRoomsNumberTextValue访问静态变量singleRoomsNumberTV，该变量由ResultsRoomInfoCustRLYT的构造函数调用的实例方法initializeAndLayoutChildren初始化。如果在创建 ResultsRoomInfoCustRLYT 的任何实例之前调用该静态方法，您将得到 NullPointerException.

Answer 2

嗯，问题是您正在尝试设置某些 null 文本视图的文本。例如，下面一行：

ResultsRoomInfoCustRLYT.setSingleRoomsNumberTextValue(singleRoomsNumberInfo);

尝试执行以下操作：

singleRoomsNumberTV.setText(singleRoomsNumberText);

但什么是 singleRoomsNumberTV？它分配在哪里？您需要致电：

new ResultsRoomInfoCustRLYT(this);

从您的 activity 初始化静态 TextView。

这些静态 getter 和 setter 方法有什么问题 - Android？

What is wrong with these static getter & setter methods - Android?

java

android

nullpointerexception

getter-setter