Question

我正在使用android studio创建一个简单的数学应用程序。我想从按钮添加减号。我有以下用于butoon的XML代码。

    <Button
        android:id="@+id/btn_minus"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_margin="@dimen/Bottom_margin"
        android:layout_weight="1"
        android:gravity="center"
        android:padding="@dimen/button_padding"
        android:text="@string/minus"
        android:textColor="@color/text_color"
        android:textSize="30sp"
        android:textStyle="bold" />

我的java类中也有这段代码。

    btn_minus= (Button) findViewById(R.id.btn_minus);
    btn_minus.setOnClickListener(this);

此按钮无效。有什么建议吗？

     public void onClick(View view)
{

    //button clicked
    if(view.getId()==R.id.enter){
        //enter button
        String answerContent = answerTxt.getText().toString();
        if(!answerContent.endsWith("?"))
        {
            //we have an answer}
            int enteredAnswer = Integer.parseInt(answerContent.substring(2));
            int exScore = getScore();

            if(enteredAnswer==answer){
                //correct
                scoreTxt.setText("Score: "+(exScore+1));
                response.setImageResource(R.drawable.correct);
                response.setVisibility(View.VISIBLE);
            }else{
                //incorrect
                scoreTxt.setText("Score: 0");
                response.setImageResource(R.drawable.wrong);
                response.setVisibility(View.VISIBLE);
            }

            chooseQuestion();
        }}
    else if(view.getId()==R.id.clear){
        //clear button
        answerTxt.setText("= ?");
    }
    else {
        //number button
        response.setVisibility(View.INVISIBLE);
        int enteredNum = Integer.parseInt(view.getTag().toString());
        if(answerTxt.getText().toString().endsWith("?"))
            answerTxt.setText("= "+enteredNum);
        else
            answerTxt.append(""+enteredNum);
    }
}

这是我得到的错误的logcat。

     --------- beginning of crash
     02-23 13:49:53.586    3996-3996/com.example.administrator.braintraininggame E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.administrator.braintraininggame, PID: 3996
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
        at com.example.administrator.braintraininggame.PlayGame.onClick(PlayGame.java:459)
        at android.view.View.performClick(View.java:4780)
        at android.view.View$PerformClick.run(View.java:19866)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Answer 1

减号不是一个整数，它会在解析为整数时崩溃

最好只添加以下代码：

else if(view.getId()==R.id.btn_minus){
    //minus button
    // substract the value
}

在XML中添加减号按钮

1 个答案: