java - 计算两个字符串时，它在 TextView 中返回为 nullnull

Question

抱歉，这是我第一次接触 Android 开发。我正在做一个计算器，例如，将这个数字与任何运算符相加，它总是

数字的范围是0-1，我选择“1”和“2”，因为按钮具有相同的java代码

代码

public void btn1_click (View v) {

    String currentTextData = tvresult.getText().toString();
    currentTextData = currentTextData + "1";
    tvresult.setText(currentTextData);
}
public void btn2_click (View v){

    String currentTextData = tvresult.getText().toString();
    currentTextData = currentTextData + "2";
    tvresult.setText(currentTextData);
}

public void btnAdd_click (View v){
    if(SystemClock.elapsedRealtime() - mlastClickTime < 1000){
        return;
    }
    mlastClickTime = SystemClock.elapsedRealtime();
    String val1 = tvresult.getText().toString();
    val1 = val1 + "+";
    add = true;
    tvresult.setText(val1);

}
public void btnSub_click (View v){
    if(SystemClock.elapsedRealtime() - mlastClickTime <1000){
        return;
    }
    mlastClickTime = SystemClock.elapsedRealtime();
    String val1 = tvresult.getText().toString();
    val1 = val1 + "-";
    sub = true;
    tvresult.setText(val1);
}


public void btnEqual_click(View v) {
    if (add) {
        val1 += val2;
        tvresult.setText(val1);
    }


}

My.xml

 <TextView
     android:id="@+id/tvresult"
     android:layout_width="200dp"
     android:layout_height="155dp"
     android:layout_alignParentRight="true"
     android:layout_alignParentEnd="true"
     android:layout_alignParentTop="true"
     android:layout_alignParentLeft="true"
     android:layout_alignParentStart="true"
     android:maxLength="18"
     android:maxLines="1"
     android:textAlignment="center"
     android:gravity="bottom"
     android:textColor="@color/colorPrimary"
     android:textSize="40sp"
     android:visibility="visible"/>

<Button
     android:id="@+id/button1"
     android:layout_width="100dp"
     android:layout_height="80dp"
     android:onClick="btn1_click"
     android:text="1"
     android:textSize="20sp"
     android:backgroundTint="@color/colorPrimaryDark"
     android:layout_above="@+id/button4"
     android:layout_alignParentLeft="true"
     android:layout_alignParentStart="true" />

<Button
    android:id="@+id/button2"
    android:layout_width="100dp"
    android:layout_height="80dp"
    android:onClick="btn2_click"
    android:text="2"
    android:textSize="20sp"
    android:backgroundTint="@color/colorPrimaryDark"
    android:layout_above="@+id/button5"
    android:layout_toRightOf="@+id/button1"
    android:layout_toEndOf="@+id/button1" />



<Button
    android:id="@+id/plus1"
    android:layout_width="wrap_content"
    android:layout_height="90dp"
    android:onClick="btnAdd_click"
    android:text="+"
    android:textSize="20sp"
    android:backgroundTint="@color/colorPrimary"
    android:textColor="@android:color/white"
    android:layout_alignTop="@id/button3"
    android:layout_toRightOf="@+id/button3"
    android:layout_toEndOf="@+id/button3"/>


<Button
    android:id="@+id/equals1"
    android:layout_width="100dp"
    android:layout_height="115dp"
    android:onClick="btnEqual_click"
    android:text="="
    android:textSize="20sp"
    android:backgroundTint="@color/colorPrimary"
    android:layout_alignTop="@+id/clear1"
    android:layout_toRightOf="@+id/clear1"
    android:layout_toEndOf="@+id/clear1" />

Answer 1

您需要将字符串类型转换为 int，例如..

Integer.parseINt(number_string);

并且您必须在将 int 值设置为 textView 中的文本之前进行类型转换，例如..

Stirng.valueOf(int_value)