单击按钮时删除字符串的最后 2/3 个字符 (Java/android)

Question

我试图在 android 上做一个 "simple" 计算器。当我单击 "Del" 按钮时，我希望删除最后一个数字。但是当我想从 EditText（计算器显示）中删除 "sin"、"cos"、"tan" 或 "ln" 时，我试图找到一种方法来删除最后 2/3 个字符而不是最后一个。

这是控制"Del"按钮点击的方法：

public void setDelOnClick(View v) {
    EditText viewCal = (EditText) findViewById(R.id.viewCal);
    int lengthView = viewCal.getText().length();
    String viewCalString = viewCal.getText().toString();
    if(lengthView == 1)
        viewCal.getText().delete(0, 1);
    else if(lengthView > 1) {
        String last2Char = viewCalString.substring(lengthView -2, lengthView);
        switch(last2Char) {
            case "in":
                viewCal.getText().delete(lengthView - 3, lengthView);
                break;
            case "os":
                viewCal.getText().delete(lengthView - 3, lengthView);
                break;
            case "ln":
                viewCal.getText().delete(lengthView - 2, lengthView);
                break;
            default:
                viewCal.getText().delete(lengthView - 1, lengthView);
                break;
        }
    }

}

但只有当我不删除 EditText 中的最后一个字符时它才有效。当我尝试删除最后一个字符时，崩溃。你能帮我想办法正确删除计算器显示屏上的内容吗？

我的轨迹

java.lang.IllegalStateException: Could not execute method of the activity
        at android.view.View.onClick(View.java:3838)
        at android.view.View.performClick(View.java:4475)
        at android.view.View$PerformClick.run(View.java:18786)
        at android.os.Handler.handleCallback(Handler.java:730)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:176)
        at android.app.ActivityThread.main(ActivityThread.java:5419)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at android.view.View.onClick(View.java:3833)

继续..

Caused by: java.lang.StringIndexOutOfBoundsException: length=1; regionStart=-1; regionLength=2
        at java.lang.String.startEndAndLength(String.java:583)
        at java.lang.String.substring(String.java:1464)
        at com.gabrielemarcozzi.mycal.MainActivity.setDelOnClick(MainActivity.java:474)

如果我的代码是：

public void setDelOnClick(View v) {
    EditText viewCal = (EditText) findViewById(R.id.viewCal);
    int lengthView = viewCal.getText().length();
    if(lengthView > 0)
        viewCal.getText().delete(lengthView - 1, lengthView);
}

我也可以删除最后一个字符，但在我想删除 "sin" 时，它变成了 "si" 等等

Answer 1

getText().clear() 是清除字段的便捷函数。 replace(0, length(), "", 0, 0)

的缩写

试试看

if(lengthView == 1)
    viewCal.getText().clear();

Answer 2

试试：

public void setDelOnClick(View v) {
    EditText viewCal = (EditText) findViewById(R.id.viewCal);
    int lengthView = viewCal.getText().length();
    String viewCalString = viewCal.getText().toString();
    if(lengthView > 0 && lengthView <=1)
        viewCal.getText().delete(lengthView - 1, lengthView);
    else
    { 
       if(lengthView > 1)
       {
          String last2Char = viewCalString.substring(lengthView -2, lengthView);

          switch(last2Char) {
           case "in":
            viewCal.getText().delete(lengthView - 3, lengthView);
            break;

           case "os":
            viewCal.getText().delete(lengthView - 3, lengthView);
            break;

           case "ln":
            viewCal.getText().delete(lengthView - 2, lengthView);
            break;

           default:
            viewCal.getText().delete(lengthView - 1, lengthView);
            break;
       }  }
    }
}

我希望现在可以使用！

单击按钮时删除字符串的最后 2/3 个字符 (Java/android)

Delete last 2/3 char of a string on button click (Java/android)

java

android

if-statement

onclick

onclicklistener