Android的Activity与Fragment之一 配置使用Activity

Android重要组成单元：Activity、Service、BroadcastReceiver、ContentProvider

实际应用中往往包括多个Activity，不同Activity向用户呈现不同的界面操作。

Android应用的多个Activity组成Activity栈，当前活动的Activity位于栈顶

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4.1 建立、配置和使用Activity

Activity间接或直接地继承了Context、ContextWrapper、ContextThemeWrapper等基类，因此可以直接调用它们的方法

配置Activity

Android应用要求所有应用程序组件（Activity、Service、ContentProvider、BroadcastReceiver）都必须显式进行配置

只需添加<activity …/>的子元素即可

name

icon

label

exported:指定该Activity是否允许被其他应用调用

launchMode:指定加载模式，支持standard、singleTop、singleTask和singleInstance这4种模式

此外，通常还会添加一个或多个<intent-filter.../>元素，该元素用于指定该Activity可响应的Intent

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4.1.3 启动、关闭Activity

虽然程序可能包含多个Activity，但只有一个Activity会作为程序的入口。

Activity启动其他Activity有如下两个方法：

startActivity(Intent intent):启动其他Activity

startActivityForResult(Intent intent, int requestCode)：以指定的请求码启动Activity。

Intent是Android应用个组件之间通信的重要方式，可以用来启动Activity，也可以用来启动Service

Activity关闭有如下方法：

finish():Activity

finishActivity(int requestCode):

示例程序代码：

public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super .onCreate(savedInstanceState);
        setContentView(R.layout. activity_main );
        Button bn = (Button) findViewById(R.id. bn );
        bn.setOnClickListener( new OnClickListener()
        {
        @Override
        public void onClick(View source)
        {
        Intent intent = new Intent(MainActivity. this , SecondActivity. class );
        startActivity(intent);
        }
        });

    }

}

第二个Activity代码:

public class SecondActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState)
{
super .onCreate(savedInstanceState);
setContentView(R.layout. second );
Button previous = (Button) findViewById(R.id. previous );
Button close = (Button) findViewById(R.id. close );
previous.setOnClickListener( new OnClickListener()
{
@Override
public void onClick(View source)
{
Intent intent = new Intent(SecondActivity. this ,
MainActivity. class );
startActivity(intent);
}
});
close.setOnClickListener( new OnClickListener()
{
@Override
public void onClick(View source)
{
Intent intent = new Intent(SecondActivity. this ,
MainActivity. class );
startActivity(intent);
finish();
}
});
}

}

当然，不可忘记在Android manifest XML文件中添加Activity定义

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4.1.4 使用Bundle在Activity之间交换数据

两个Activity之间有一个信使Intent，我们只要将需要交换的数据放入Intent即可。Intent提供了多个方法来携带额外数据：

putExtras(Bundle data)	向Intent中放入需要携带的数据包
Bundle getExtras()	取出Intent所携带的数据包
putExtras(String name, Xxx value)	向Intent中按key-value对的形式存入数据
getXxxExtras(String name)	从Intent中按key取出指定类型的数据

上面的Bundle就是一个简单的数据携带包，该Bundle对象包含了多个方法来存入数据：

• putXxx(String key, Xxx data)：向Bundle放入Int、Long等各种类型数据
• putSerializable(String key, Serializable data):从Bundle取出一个可序列化的对象

示例代码：

main.java

public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super .onCreate(savedInstanceState);
        setContentView(R.layout. activity_main );
        Button bn = (Button) findViewById(R.id. bn );
        bn.setOnClickListener( new OnClickListener()
        {
        public void onClick(View v)
        {
        EditText name = (EditText) findViewById(R.id. name );
        EditText passwd = (EditText) findViewById(R.id. password );
        RadioButton male = (RadioButton) findViewById(R.id. male );
//        RadioButton female = (RadioButton) findViewById(R.id.female);
        String gender = male.isChecked()? "male" : "female" ;
        Person p = new Person(name.getText().toString(), passwd.getText().toString(), gender);
        Bundle data = new Bundle();
        data.putSerializable( "person" , p);
        Intent intent = new Intent(MainActivity. this , ResultActivity. class );
        intent.putExtras(data);
        startActivity(intent);
        }
        });

    }

}

ResultActivity.java————

public class ResultActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super .onCreate(savedInstanceState);
setContentView(R.layout. result );
TextView name = (TextView) findViewById(R.id. name );
TextView passwd = (TextView) findViewById(R.id. password );
TextView gender = (TextView) findViewById(R.id. gender );
Intent intent = getIntent();
Person p = (Person) intent.getSerializableExtra( "person" );
name.setText( "your acount name :" + p.getName());
passwd.setText( "your password :" + p.getPass());
gender.setText( "your gender :" + p.getGender());

}

}

main Activity布局文件：

< TableLayout 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:orientation = "vertical" >

    < TextView
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:text = "please input your register information"
        android:textSize = "20sp" />

    < TableRow >

        < TextView
            android:layout_width = "match_parent"
            android:layout_height = "wrap_content"
            android:text = "user name"
            android:textSize = "20sp" />

        < EditText
            android:id = "@+id/name"
            android:layout_width = "match_parent"
            android:layout_height = "wrap_content"
            android:hint = "enter your account"
            android:selectAllOnFocus = "true" />
    </ TableRow >

    < TableRow >

        < TextView
            android:layout_width = "match_parent"
            android:layout_height = "wrap_content"
            android:text = "code:"
            android:textSize = "16sp" />

        < EditText
            android:id = "@+id/password"
            android:layout_width = "match_parent"
            android:layout_height = "wrap_content"
            android:password = "true"
            android:selectAllOnFocus = "true" />
    </ TableRow >

    < TableRow >

        < TextView
            android:layout_width = "match_parent"
            android:layout_height = "wrap_content"
            android:text = "gender:"
            android:textSize = "16sp" />

        < RadioGroup
            android:layout_width = "wrap_content"
            android:layout_height = "wrap_content"
            android:orientation = "horizontal" >

            < RadioButton
                android:id = "@+id/male"
                android:layout_width = "wrap_content"
                android:layout_height = "wrap_content"
                android:text = "male"
                android:textSize = "16sp" />

            < RadioButton
                android:id = "@+id/female"
                android:layout_width = "wrap_content"
                android:layout_height = "wrap_content"
                android:text = "female"
                android:textSize = "16sp" />
        </ RadioGroup >
    </ TableRow >

    < Button
        android:id = "@+id/bn"
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:text = "register"
        android:textSize = "16sp" />

</ TableLayout >

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4.1.5 启动其他Activity并返回结果

Activity还提供了一个startActivityForResult(Intent intent, int requestCode)

这种启动其他Activity并返回结果的场景也是通过Bundle进行数据交换的，为了获取Activity所返回的结果，需要从两方面着手：

1. 当前Activity需要重写onActivityResult(int requestCode, int resultCode, Intent intent),当被启动Activity返回结果时该方法会被触发。resultCode代表Activity返回的结果码，这个结果码由开发者根据业务自行设定
2. 被启动Activity需要调用setResult()方法设置处理结果