Android 如果语句失败

Question

我正在使用这个简单的 if/else 语句来检查选择了哪个 RadioButton 并设置有关选择的 TextView 的文本。好吧，对于前两种情况（if rb1.isChecked() 和 if rb2.isChecked()），代码正确执行，它只是计算两个数字。但是，当出现第三种情况时 (!rb1.isChecked() && !rb2.isChecked()) 应用程序崩溃了。怎么了？

        if (rb1.isChecked()) {
        int sum = x + y;
        String result = String.valueOf(sum);
        tv3.setText(result);
    } else if (rb2.isChecked()) {
        int rest = x - y;
        String result = String.valueOf(rest);
        tv3.setText(result);
    } else if (!rb1.isChecked() && !rb2.isChecked()){
        tv3.setText("Select an option!");
    }

更新：
Manifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.logixor.advancedcalc">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest>

MainActivity.java:

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
public EditText et1,et2;
public TextView tv3;
public RadioButton rb1,rb2;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    et1=(EditText)findViewById(R.id.et1);
    et2=(EditText)findViewById(R.id.et2);
    tv3=(TextView)findViewById(R.id.tv3);
    rb1=(RadioButton)findViewById(R.id.rb1);
    rb2=(RadioButton)findViewById(R.id.rb2);
}

public void calc(View view) {
    String valA = et1.getText().toString();
    String valB = et2.getText().toString();
    int x = Integer.parseInt(valA);
    int y =Integer.parseInt(valB);

    if (rb1.isChecked()) {
        int sum = x + y;
        String result = String.valueOf(sum);
        tv3.setText(result);
    } else if (rb2.isChecked()) {
        int rest = x - y;
        String result = String.valueOf(rest);
        tv3.setText(result);
    }

    if (!rb1.isChecked() && !rb2.isChecked()){
        tv3.setText("Select an option!");
    }
}
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.logixor.advancedcalc.MainActivity">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/textNumber"
    android:id="@+id/tv2"
    android:layout_marginTop="27dp"
    android:layout_below="@+id/et1"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true" />

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:inputType="number"
    android:ems="10"
    android:id="@+id/et2"
    android:layout_below="@+id/tv2"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:hint="@string/writeHere" />

<RadioGroup
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="29dp"
    android:padding="20dp"
    android:layout_below="@+id/et2"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:id="@+id/rg1">

    <RadioButton
        android:text="@string/sum"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/rb1"
        android:layout_weight="1" />

    <RadioButton
        android:text="@string/rest"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/rb2"
        android:layout_weight="1" />

</RadioGroup>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/textNumber"
    android:layout_marginTop="25dp"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:id="@+id/tv1" />

<Button
    android:text="@string/calc"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/button"
    android:layout_alignBottom="@+id/rg1"
    android:layout_marginBottom="27dp"
    android:layout_alignParentRight="true"
    android:layout_alignParentEnd="true"
    android:layout_toRightOf="@+id/rg1"
    android:layout_toEndOf="@+id/rg1"
    android:onClick="calc" />

<TextView
    android:text="@string/result"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="19dp"
    android:id="@+id/tv3"
    android:textSize="24sp"
    android:layout_below="@+id/rg1"
    android:textAlignment="center" />

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:inputType="number"
    android:ems="10"
    android:layout_marginTop="8dp"
    android:id="@+id/et1"
    android:hint="@string/writeHere"
    android:layout_below="@+id/tv1"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true" />

</RelativeLayout>

strings.xml:

<resources>
<string name="app_name">AdvancedCalc</string>
<string name="textNumber">Number</string>
<string name="writeHere">Write number here...</string>
<string name="result">Result</string>
<string name="calc">CALCULATE</string>
<string name="sum">Sum</string>
<string name="rest">Rest</string>
</resources>

来自 logcat 的致命错误：

E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.logixor.advancedcalc, PID: 23911
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:4640)
at android.view.View$PerformClick.run(View.java:19425)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5593)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:4640) 
at android.view.View$PerformClick.run(View.java:19425) 
at android.os.Handler.handleCallback(Handler.java:733) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:146) 
at android.app.ActivityThread.main(ActivityThread.java:5593) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099) 
at dalvik.system.NativeStart.main(Native Method) 
Caused by: java.lang.NumberFormatException: Invalid int: ""
at java.lang.Integer.invalidInt(Integer.java:137)
at java.lang.Integer.parseInt(Integer.java:358)
at java.lang.Integer.parseInt(Integer.java:331)
at com.logixor.advancedcalc.MainActivity.calc(MainActivity.java:30)
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
at android.view.View.performClick(View.java:4640) 
at android.view.View$PerformClick.run(View.java:19425) 
at android.os.Handler.handleCallback(Handler.java:733) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:146) 
at android.app.ActivityThread.main(ActivityThread.java:5593) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099) 
at dalvik.system.NativeStart.main(Native Method)

Answer 1

1)使用try catch语句理解错误！
也许 tv 等于 null .
2) 不用else if (!rb1.isChecked() && !rb2.isChecked())，直接用else{}
试试这个：

    try{
       if(tv == null)
       {
          Toast.makeText(getBaseContext(),"tv is null", 
                Toast.LENGTH_SHORT).show();
          return;
       }
    if (rb1.isChecked()) {
            int sum = x + y;
            String result = String.valueOf(sum);
            tv3.setText(result);
        } else if (rb2.isChecked()) {
            int rest = x - y;
            String result = String.valueOf(rest);
            tv3.setText(result);
        } else{
            tv3.setText("Select an option!");
        }
    }
    catch(Exception e)
    {
      Toast.makeText(getBaseContext(),"Err:"+r.toString(), 
                Toast.LENGTH_SHORT).show();
    }

Answer 2

Caused by: java.lang.NumberFormatException: Invalid int: "" 表示 EditText 中的文本为空，因此您在 calc() 函数内部的 Integer.parseInt() 处得到异常。使用 TextUtils.isEmpty(). Additionally you might make use of TextUtils.isDigitsOnly().

检查它是否为空

编辑

使用 EditText 的 android:inputType="number" xml 属性，您将使其只接受数字。

Android 如果语句失败

Android If statement fails

java

android

string

android-edittext

numberformatexception