java - 一个类中存在两个单击监听器的问题

Question

需要一些帮助来创建我的主菜单。我已经成功制作了一个点击监听器，可以切换到不同的 Activity ，但我在让第二个监听器工作时遇到了麻烦。该应用程序在模拟中运行良好，但当我点击“重量 Gin ”按钮时，什么也没有发生。我似乎找不到问题

      package com.example.bmiworking;

    import android.app.Activity;
    import android.content.DialogInterface;
    import android.view.View.OnClickListener;
    import android.content.Intent;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.Button;
    import android.widget.EditText;
    import android.widget.TextView;

    public class MainMenu extends Activity implements OnClickListener {
    /** Called when the activity is first created. */
    Button btn,btn1,btn2,btn3;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.mainmenu);
        btn = (Button) findViewById(R.id.buttonBMI);
        btn.setOnClickListener(this);
        btn1 = (Button) findViewById(R.id.buttonGain);
        btn1.setOnClickListener(this);
    }

        @Override
    public void onClick(View v) {
        if (v.getId() == R.id.buttonBMI) {
            startActivity(new Intent(this, MainActivity.class));
        }
    }
        public void onClick1(View d) {
            if (d.getId() == R.id.buttonGain) {
                startActivity(new Intent(this, weightgain.class));
            }
        }
    }


package com.example.bmiworking;

import android.os.Bundle;
import android.app.Activity;
import android.content.DialogInterface;
import android.view.View.OnClickListener;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class weightgain extends Activity {
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.weightgain);
}
}


<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    tools:context=".StartingPoint" 
    android:background="@drawable/grunge">

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Main Menu"
        android:textSize="45dp"
        android:layout_gravity="center"
        android:gravity="center" 
        android:id="@+id/tvDisplay"/>

    <Button
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:text="BMI Goal" 
        android:layout_gravity="center"
        android:textSize="20dp"
         android:id="@+id/bSub"/>

    <Button
        android:id="@+id/buttonBMI"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="BMI Calculator"
        android:textSize="20dp" />

    <Button
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:text="Muscle Loss Workouts" 
        android:layout_gravity="center"
        android:textSize="20dp"
         android:id="@+id/bSub"/>

    <Button
        android:id="@+id/buttonGain"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="Muscle Gain Workouts"
        android:textSize="20dp" />

</LinearLayout>



<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.bmiworking"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />

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

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.example.bmiworking.MainMenu"
            android:label="@string/app_name" >
            </activity>
            <activity
            android:name="com.example.bmiworking.weightgain"
            android:label="@string/app_name" >
            </activity>
    </application>

使用堆栈跟踪进行编辑:

  01-24 02:34:34.739: D/dalvikvm(808): newInstance failed: p0 i0 [0 a1
    01-24 02:34:34.754: D/AndroidRuntime(808): Shutting down VM
    01-24 02:34:34.754: W/dalvikvm(808): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
    01-24 02:34:34.819: E/AndroidRuntime(808): FATAL EXCEPTION: main
    01-24 02:34:34.819: E/AndroidRuntime(808): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.bmiworking/com.example.bmiworking.MainMenu}: java.lang.InstantiationException: can't instantiate class com.example.bmiworking.MainMenu
    01-24 02:34:34.819: E/AndroidRuntime(808):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at android.os.Handler.dispatchMessage(Handler.java:99)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at android.os.Looper.loop(Looper.java:137)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at android.app.ActivityThread.main(ActivityThread.java:5039)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at java.lang.reflect.Method.invokeNative(Native Method)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at java.lang.reflect.Method.invoke(Method.java:511)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at dalvik.system.NativeStart.main(Native Method)
    01-24 02:34:34.819: E/AndroidRuntime(808): Caused by: java.lang.InstantiationException: can't instantiate class com.example.bmiworking.MainMenu
    01-24 02:34:34.819: E/AndroidRuntime(808):  at java.lang.Class.newInstanceImpl(Native Method)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at java.lang.Class.newInstance(Class.java:1319)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
    01-24 02:34:34.819: E/AndroidRuntime(808):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
    01-24 02:34:34.819: E/AndroidRuntime(808):  ... 11 more

Answer 1

将 onClick 代码更改为使用 switch case 而不是 if-else :

@Override
public void onClick(View v) {
 switch(v.getId()){
  case R.id.buttonBMI: 
          startActivity(new Intent(this, MainActivity.class));
       break;

  case R.id.buttonGain:  
       startActivity(new Intent(this, weightgain.class));
       break;
  }
}