Question

我有一个类似于对话框的类：

interface DiagInterface{
void selectionDone(boolean accepted);
}

public class CardSelectionDialog extends Dialog {

private android.view.View.OnClickListener positive;
private android.view.View.OnClickListener negative;
private boolean AcceptState;
private DiagInterface ExtComm;

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

    AcceptState = false;

    positive = new android.view.View.OnClickListener() {            
        @Override
        public void onClick(View v) {
            AcceptState = true;
            OnSelectionDone();
            dismiss();
        }
    };

    negative= new android.view.View.OnClickListener() {         
        @Override
        public void onClick(View v) {
            AcceptState = false;
            OnSelectionDone();
            dismiss();
        }
    };      

}

private void OnSelectionDone(){
    System.err.println("Before selection");
    ExtComm.selectionDone(AcceptState);
}

然后在我的主要课程上，我有以下内容：

这是我调用对话框（MainActivity）的地方：

public void SelectCardDialog(){
    CardSelectionDialog diag = new CardSelectionDialog(this);
    CardDeck deck = new CardDeck();
    deck.addNOfCard(CardType.WOUNDCARD, 30, this);
    diag.setSelection(deck);
    diag.show();
}

这是interfase的实现：

@Override
public void selectionDone(boolean accepted){
    if (accepted){
        System.err.println("ACCEPTED");
    }
    else{
        System.err.println("REJECTED");
    }       
}

然而，每当我按下任何按钮时，我都会收到以下错误（出现选择前信息）

01-01 16:59:42.180: E/AndroidRuntime(29810): java.lang.NullPointerException
01-01 16:59:42.180: E/AndroidRuntime(29810):    at legen.dary.CardSelectionDialog.OnSelectionDone(CardSelectionDialog.java:106)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at legen.dary.CardSelectionDialog.access$1(CardSelectionDialog.java:103)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at legen.dary.CardSelectionDialog$1.onClick(CardSelectionDialog.java:35)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at android.view.View.performClick(View.java:4084)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at android.view.View$PerformClick.run(View.java:16966)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at android.os.Handler.handleCallback(Handler.java:615)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at android.os.Handler.dispatchMessage(Handler.java:92)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at android.os.Looper.loop(Looper.java:137)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at android.app.ActivityThread.main(ActivityThread.java:4745)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at java.lang.reflect.Method.invokeNative(Native Method)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at java.lang.reflect.Method.invoke(Method.java:511)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-01 16:59:42.180: E/AndroidRuntime(29810):    at dalvik.system.NativeStart.main(Native Method)

我做错了什么想法？

非常感谢.....

Answer 1

您尚未初始化

 private DiagInterface ExtComm;

你可能想要

public CardSelectionDialog(Context context){
super(context); 
ExtComm= (DiagInterface)context;
AcceptState = false;
}

此外，您可能希望在构造函数外部移动

 positive = new android.view.View.OnClickListener() {            
    @Override
    public void onClick(View v) {
        AcceptState = true;
        OnSelectionDone();
        dismiss();
    }
 };

negative= new android.view.View.OnClickListener() {         
    @Override
    public void onClick(View v) {
        AcceptState = false;
        OnSelectionDone();
        dismiss();
    }
};

Answer 2

我认为这个NPE异常来自这一行：

ExtComm.selectionDone(AcceptState);

可能ExtComm为空

Android上的接口调用上的空指针异常

2 个答案: