Suddently, “R.java” was deleted from my “CheckBox”

问题:

I'm learning Android (I'm a beginner) and making a program for CheckBox.
Everything seems fine, but when I cleaned my project suddenly, R.java was deleted and it's giving an error.
I checked three times, but not getting it back.

Here is my source code:

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <CheckBox
        android:id="@+id/checkBox1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="IPhone" />

    <CheckBox
        android:id="@+id/checkBox2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Android" 
        android:checked="true"/>

    <CheckBox
        android:id="@+id/checkBox3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Windows Mobile"
        android:checked="false"/>

    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Display" />

</LinearLayout>

MainActivity.java

package com.example.lesson06;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.Toast;

public class MainActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        addListenerOnButton();
        addListenerOnChkbox();
    }
    public void addListenerOnChkbox(){
        CheckBox chkbx=(CheckBox)findViewById(R.id.checkBox1);
        chkbx.setOnClickListener(new OnClickListener(){

            public void onClick(View v){
                if(((CheckBox) v).isChecked()){
                    Toast.makeText(MainActivity.this, "Bro..try Android :)", Toast.LENGTH_LONG);
                }
            }
        });
    }

    public void addListenerOnButton(){
        final CheckBox chkbx=(CheckBox)findViewById(R.id.checkBox1);
        final CheckBox chkbx2=(CheckBox)findViewById(R.id.checkBox2);
        final CheckBox chkbx3=(CheckBox)findViewById(R.id.checkBox3);
        final Button btn=(Button)findViewById(R.id.btn);

        btn.setOnClickListener(new OnClickListener(){
            public void onClick(View v){
                StringBuffer result=new StringBuffer();
                result.append("IPhone check: ").append(chkbx.isChecked());
                result.append("\nAndroid check: ").append(chkbx2.isChecked());
                result.append("\nWindows Mobile Check: ").append(chkbx3.isChecked());

                Toast.makeText(MainActivity.this, result.toString(), Toast.LENGTH_LONG).show();
            }
        });
    }
}

Any help would be greatly appreciated.

回答1:

Your Button Tag not closed into activity_main.xml

<Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Display"

Close that

<Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Display" />

and clean project. Your R.java class will be generated.

回答2:

Change your button to the following:

<Button
    android:id="@+id/btn"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Display"/>

It seems you forgot to close the button tag, so AAPT could not generate a new R.class.

回答3:

Generally R.java is not created when you have errors on one or more xml files. In this case the error is in the Button tag (the IDE should warn you about that error).