任务三：：理解Task。

一、运行效果图。二、核心代码。Mainactivity：package com.example.androidtask;import android.net.Uri;import android.os.Bundle;import android.app.Activity;import android.content.Intent;import android.view.Menu;import android.view.View;import android.widget.Button;import android.view.View.OnClickListener;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);Button btnToSecond = (Button) this.findViewById(R.id.btnToSecond);btnToSecond.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View arg0) {// TODO Auto-generated method stubIntent intent = new Intent(MainActivity.this,SecondActivity.class);startActivity(intent);}});Button btn_call = (Button) this.findViewById(R.id.btn_call);btn_call.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stub//打给移动10086Intent intent =new Intent(Intent.ACTION_DIAL);intent.setData(Uri.parse("tel:10086"));startActivity(intent);}});}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.main, menu);return true;}}

SecondActivity:

package com.example.androidtask;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.widget.Button;

public class SecondActivity extends Activity {

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

Button btnToFirst = (Button) this.findViewById(R.id.btnToFirst);
btnToFirst.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
Intent intent = new Intent(SecondActivity.this,
MainActivity.class);
startActivity(intent);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.second, menu);
return true;
}

}

ThirdActivity:package com.example.androidtask;import android.app.Activity;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;public class ThirdActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_third);}}布局：<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"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=".MainActivity" ><Buttonandroid:id="@+id/btn_call"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentBottom="true"android:layout_centerHorizontal="true"android:layout_marginBottom="186dp"android:onClick="clickHandler"android:text="call" /><Buttonandroid:id="@+id/btnToSecond"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentTop="true"android:layout_centerHorizontal="true"android:layout_marginTop="66dp"android:onClick="btnToSecond"android:text="btnToSecond" /></RelativeLayout>

<pre name="code" class="html"><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"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=".SecondActivity" ><Buttonandroid:id="@+id/btnToFirst"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentTop="true"android:layout_centerHorizontal="true"android:layout_marginTop="150dp"android:onClick="btnToFirst"android:text="btnToFirst" /></RelativeLayout>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context="${relativePackage}.${activityClass}" ></RelativeLayout>三、编程中遇到的问题。刚开始调用打电话的时候出现了问题，没有建立第三个Activity然后用按钮去调用。导致运行出错。后来查资料询问同学。才知道问题的关键。之后得以解决。