Android 简单的按钮事件

今天编写了一个小程序，运行的时候总是出现如下的错误



找了好久，问了eoeAndroid群里的高手们才知道，我把setContentView(R.layout.main)放到了，后面，应该将其放到onCreate最前面，如下

package org.loulijun.test;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.LinearLayout;

public class HelloActivity extends Activity{
/** Called when the activity is first created. */
private Button blue;
private Button yellow;
LinearLayout linearLayout;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
linearLayout=(LinearLayout)this.findViewById(R.id.linearLayout);

blue=(Button)findViewById(R.id.blueButton);
yellow=(Button)findViewById(R.id.yellowButton);

blue.setOnClickListener(new ButtonListener());
yellow.setOnClickListener(new ButtonListener());

}

class ButtonListener implements OnClickListener
{

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
switch(v.getId())
{
case R.id.blueButton:
linearLayout.setBackgroundColor(Color.BLUE);
break;
case R.id.yellowButton:
linearLayout.setBackgroundColor(Color.YELLOW);
break;
}
}

}

}

----------------------------------------

另外就是要为LinearLayout设置一个Id，然后通过ID来找到这个布局文件，后面的事件里才能够通过

linearLayout.setBackgroundColor(Color.BLUE);
设置背景颜色

main.xml文件如下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/linearLayout"
>
<Button
android:id="@+id/blueButton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/blue"
/>
<Button
android:id="@+id/yellowButton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"

android:text="@string/yellow"
/>
</LinearLayout>

运行结果是