安卓.Activity

在AndroidManifast注册activity，欲想运行一个Activity，得先注册

<activity
            android:name=".FirstActivity"
            android:label="This is my first Activity" //标题栏
            >
            <intent-filter >

//让FirstActivity，作为主Activity
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>

===========

Toast的应用


Toast.makeText(FirstActivity.this, "show Toast", Toast.LENGTH_LONG).show();
//.makeText返回Toast对象，再调用show方法

FirstActivity.this,在哪个Activity显示

====================


启动第二个Activity

先注册Activity：
<activity
android:name=".SecondActivity"    //类名       
            >
        </activity>


//点击button，启动另外一个Activity
class Listener2 implements OnClickListener{

@Override
public void onClick(View v) {
//FirstActivity.this，当前的Activity
//SecondActivity.class,想要启动的Activity
Intent intent = new Intent(FirstActivity.this, SecondActivity.class);

startActivity(intent);//启动Activity
}

==========================

用Intent，指定Android内置的动作

Intent intent = new Intent(Intent.ACTION_DIAL);//指定Intent，打电话

//指定Intent对象要操作的数据
//一般通过字符串传送，由Uri解析
intent.setData(Uri.parse("tel:10086"));
startActivity(intent);//启动Activity


=========================

向下一个Activity传递数据


public void onClick(View v) {
Intent intent = new Intent(FirstActivity.this,SecondActivity.class);

String data="1234qwer";

//向下一个Activity传递数据
//key,键；data，值
intent.putExtra("key", data);
startActivity(intent);
}

//得到传递过来的数据
//获得当前Activity的Intent
Intent intent = getIntent();
String string = intent.getStringExtra("key");//得到传递过来的数据
Log.d("SecondActivity", string);
Toast.makeText(SecondActivity.this, string, Toast.LENGTH_LONG).show();

==========================

返回数据给上一个Activity

step1
public void onClick(View v) {

Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
startActivityForResult(intent, 1);// 返回数据给上一个Activity
}

step2
@Override
public void onClick(View v) {
Intent intent = new Intent();
intent.putExtra("key1", "value1");

setResult(RESULT_OK, intent);//向上一个Activity，返回数据
finish();//销毁Activity
}

step3
//复写
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
switch (requestCode) {
case 1:
if (resultCode == RESULT_OK) {
String string = data.getStringExtra("key1");
Log.d("SecondActivity", string);
}
break;

default:
break;
}
}

================================

知晓当前是在哪个Activity

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

//获取当前实例的类名
//并通过log打印出来
Log.d("MainActivity", getClass().getSimpleName());
}