2017-11-17

Android的activity

Activity 是什么

简述：

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Activity 是一个应用组件，用户可与其提供的屏幕进行交互，以执行拨打电话、拍摄照片、发送电子邮件或查看地图等操作。
每个 Activity 都会获得一个用于绘制其用户界面的窗口。窗口通常会充满屏幕，但也可小于屏幕并浮动在其他窗口之上。
(类似UIViewController)

创建：创建Activity必须要在AndroidManifest.xml声明Activity。

<manifest ... >
  <application ... >
      <activity android:name=".ExampleActivity" />
      ...
  </application ... >
  ...
</manifest >

设置intent-filter：创建项目时，自动创建默认启动的MainActivity。

<activity android:name=".MainActivity" android:icon="@drawable/app_icon">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

Activity 启动：

无回调：startActivity()。ExampleActivity是要启动的Activity

1 2	Intent intent = new Intent(this, ExampleActivity.class); startActivity(intent);

有回调：startActivityForResult()。需实现回调：onActivityResult

ExampleRequestCode = 2;//请求码：用于区分哪个Activity的回调

Intent intent = new Intent(this, ExampleActivity.class);
startActivityForResult(intent,ExampleRequestCode);

@Override  
protected void onActivityResult(int requestCode, int resultCode, Intent data) {  
    super.onActivityResult(requestCode, resultCode, data);  
    if (requestCode == ExampleRequestCode && resultCode == Activity.RESULT_OK) {  
    }  
}

-- ExampleActivity--
resultCode = 1;//结果码：用于区分回调方法的状态
void finishActivity() {  
    Intent intent = new Intent();  
    intent.putExtra("param", "1");  
    setResult(resultCode,intent);  
    finish();  
}

传值：启动时可以用Intent和bundle传参数。

-- Intent -- 
Intent intent = new Intent(this, ExampleActivity.class);
intent.putExtra("age", 25);
intent.putExtra("address", "guangzhou");
startActivity(intent);

ExampleActivity:
Intent intent = getIntent();  
int age = intent.getIntExtra("age",0);  
String addressString = intent.getStringExtra("address");

-- Bundle -- 
Intent intent = new Intent(this, ExampleActivity.class);
Bundle bundle = new Bundle();
bundle.putInt("age", 25);
bundle.putString("address", "guangzhou");
intent.putExtras(bundle); 
startActivity(intent);

ExampleActivity:
Intent intent = getIntent(); 
Bundle bundle = intent.getExtras(); 
int age = bundle.getInt("age"); 
String addressString = bundle.getString("address");

Activity 结束/关闭：

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finish(); //关闭当前页面
Activity.finish();//关闭某个Activity
System.exit(0); //退出程序

Activity生命周期：

Activity生命周期

public class ExampleActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // The activity is being created.
        //首次创建 Activity 时调用。 您应该在此方法中执行所有正常的静态设置 — 创建视图、将数据绑定到列表等等(ViewDidLoad)
    }
    @Override
    protected void onReStart() {
        super.onStart();
        //在 Activity 已停止并即将再次启动前调用。
    }
    @Override
    protected void onStart() {
        super.onStart();
        // The activity is about to become visible.
        //在 Activity 即将对用户可见之前调用。(ViewWillAppear)
    }
    @Override
    protected void onResume() {
        super.onResume();
        // The activity has become visible (it is now "resumed").
        //在 Activity 即将开始与用户进行交互之前调用。(ViewDidAppear)
    }
    @Override
    protected void onPause() {
        super.onPause();
        // Another activity is taking focus (this activity is about to be "paused").
        //当系统即将开始继续另一个 Activity 时调用。
        此方法通常用于确认对持久性数据的未保存更改、停止动画以及其他可能消耗 CPU 的内容，诸如此类。
        (ViewWillDisAppear)
    }
    @Override
    protected void onStop() {
        super.onStop();
        // The activity is no longer visible (it is now "stopped")
        //在 Activity 对用户不再可见时调用。(ViewDidDisAppear)
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        // The activity is about to be destroyed.
        //在 Activity 被销毁前调用.(dealloc)
    }
}