何时PendingIntent被处置/删除？(When exactly does a PendingIntent get disposed/removed?)

 根据文档 ，在API级别17中添加的View.generateViewId()将生成适合在setId(int)使用的值。 此值不会与构建时在aid为R.id生成的ID值冲突。 
 
 我尝试使用View.generateViewId()来了解它的行为方式。 以下是我的发现。 
 
 
 
 生成的ID将从1开始，每次调用时都会递增（1,2,3 ......） 
 
 
 generateViewId() 将保留返回的最后一个ID ，并将在整个应用程序生命周期中从那里继续。 例如，如果设备旋转前的最后一个ID为4，则旋转后的下一个ID将为5。 
 
 
 重要的是要注意，例如，如果您在应用程序的onCreate()方法中通过每次调用generateViewId()在运行时设置视图，则在设备旋转后，默认情况下会再次调用onCreate()并且您的视图将会获得与轮换前不同的ID 。 
 
 Android具有自动恢复视图状态的功能 - 例如，您输入EditText视图的文本，检查CheckBox的状态 - 在设备轮换后，但它仅在视图具有持久ID时才有效 。 因此，在上面的示例中，此状态恢复将不起作用 - 您的EditText视图将丢失输入，您必须键入您需要再次键入的内容 - 因为视图每次生成时都会收到不同的ID。 要解决此问题，您需要通过活动生命周期维护ID。 
 
 我发现Android为数十亿的XML中定义的对象分配ID。 这是从我的应用程序中获取的具有几个预定义ID的真实ID：2131427423。因此，在不调用generateViewId()情况下自行判断使用低ID 似乎是非常安全的。 在我的简单应用程序中，我通过分配从1开始的ID，增加1来模仿它，并且它起作用。 这是一个从我的应用程序中提取的示例： 
 
public class MainActivity extends AppCompatActivity {
    // since our lastAllocatedViewId will reset on device rotation
    // regenerated views will receive the same ID
    private int lastAllocatedViewId = 0;

    private ArrayList<QuizQuestions> quizQuestions;

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

        // read quizQuestions from xml at runtime;
        quizQuestions = parseQuizQuestionsXml();

        // we will dynamically add quiz question views to this view
        // depending on how many quizQuestions are in the XML config
        LinearLayout container = (LinearLayout) findViewById(R.id.quiz_questions_container);

        // generate a view for each quiz question
        for (int i = 0; i < quizQuestions.size(); i++) {
            LinearLayout quizQuestionView = (LinearLayout) inflater.inflate(R.layout.quiz_question_template, parent, false);

            quizQuestionView.setId(lastAllocatedViewId++);

            (...) // do some work on our newly generated view

            // then add it to the quiz questions container
            container.addView(quizQuestionView);
        }
    }
}

According to the documentation, View.generateViewId() added in API level 17 will generate a value suitable for use in setId(int). This value will not collide with ID values generated at build time by aapt for R.id.
 
I experimented with View.generateViewId() to find out how it behaves. Here are my findings.
 
 
 
Generated ID will begin from 1 and will be incremented by each time it is called (1, 2 , 3...)
 
 
generateViewId() will maintain the last ID returned and will continue from there throughout app life cycle. For example if last ID before device rotation was 4, next ID after rotation will 5.
 
 
It is important to note that, for instance, if you are setting up views at runtime in your app's onCreate() method by calling generateViewId() every time, after your device rotates, by default onCreate() is called again and your views will receive a different ID than before rotation. 
 
Android has a feature to automatically restore your views state – for instance, text you enter into an EditText view, checked state of a CheckBox – after device rotation, but it only works if the views' have persistent IDs. So in the above example, this state restoration will not work – your EditText view will lose input and you have to type whatever you need to type in again – as views will receive a different ID every time they are generated. To work around this problem, you need to maintain IDs through activity life cycle.
 
I found out that Android assigns IDs for objects defined in XML in the magnitude of billions. This is a real life ID taken from my app having only a few predefined IDs: 2131427423. So it seems to be pretty safe to use low IDs on your own discretion without ever calling generateViewId(). In my simple app I mimicked it by assigning IDs beginning from 1, increasing by one, and it worked. Here is an example, extracted from my app:
 
public class MainActivity extends AppCompatActivity {
    // since our lastAllocatedViewId will reset on device rotation
    // regenerated views will receive the same ID
    private int lastAllocatedViewId = 0;

    private ArrayList<QuizQuestions> quizQuestions;

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

        // read quizQuestions from xml at runtime;
        quizQuestions = parseQuizQuestionsXml();

        // we will dynamically add quiz question views to this view
        // depending on how many quizQuestions are in the XML config
        LinearLayout container = (LinearLayout) findViewById(R.id.quiz_questions_container);

        // generate a view for each quiz question
        for (int i = 0; i < quizQuestions.size(); i++) {
            LinearLayout quizQuestionView = (LinearLayout) inflater.inflate(R.layout.quiz_question_template, parent, false);

            quizQuestionView.setId(lastAllocatedViewId++);

            (...) // do some work on our newly generated view

            // then add it to the quiz questions container
            container.addView(quizQuestionView);
        }
    }
}