android_example_1:安卓
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【Android:使用活动】 在Android应用开发中,活动(Activity)是用户界面的基本构建块,它是用户与应用程序交互的窗口。Android应用通常由一个或多个活动组成,每个活动对应一个屏幕或者一个特定的功能。理解并熟练掌握活动的使用是成为专业Android开发者的关键。 1. **活动生命周期** - 活动的生命周期包括创建(onCreate())、启动(onStart())、可见(onResume())、暂停(onPause())、停止(onStop())、销毁(onDestroy())等几个阶段。开发者需要了解这些回调方法何时被调用,以便在适当的时候保存和恢复数据,优化性能。 2. **启动模式** - Android活动有四种启动模式:标准模式、单实例模式、单任务模式和单栈顶模式。选择合适的启动模式可以决定活动如何在任务栈中被管理和用户如何返回到它。 3. **Intent与Activity间通信** - Intent是Android系统中启动活动的主要手段,它封装了动作、数据和目标组件等信息。通过startActivity()或startActivityForResult()方法,可以使用Intent启动新的活动或者与已存在的活动进行交互。 4. **回退栈管理** - Android系统维护了一个回退栈来管理活动,新启动的活动会被压入栈顶,当按下回退键时,栈顶的活动会被弹出。开发者可以通过设置FLAG_ACTIVITY_CLEAR_TOP或FLAG_ACTIVITY_SINGLE_TOP等标志来控制栈的行为。 5. **配置变化处理** - 当设备的配置(如屏幕方向、语言设置等)发生变化时,系统默认会销毁并重新创建活动。通过重写onSaveInstanceState()和onRestoreInstanceState(),或使用onConfigurationChanged()方法,开发者可以处理配置变化,避免不必要的活动重建。 6. **活动的透明度与主题** - 开发者可以设置活动的主题和背景,使其具有不同的视觉效果。例如,通过设置透明主题可以使活动背景透明,实现悬浮窗口的效果。 7. **多窗口支持** - 自Android Nougat(7.0)开始,引入了多窗口模式,允许活动同时在屏幕上显示为小窗口或分屏模式。开发者需要适配这种模式,确保活动在不同尺寸下仍能正常工作。 8. **内存优化** - 当系统资源紧张时,Android可能会销毁后台活动。因此,开发者应确保活动在onPause()和onStop()方法中释放资源,如网络连接、数据库操作等,以避免内存泄漏。 9. **启动意图过滤器** - 使用<intent-filter>标签,可以声明活动能够响应哪些类型的Intent,使得其他应用可以通过Intent启动该活动,增加了应用的可发现性和交互性。 10. **返回结果** - 如果需要从一个活动返回结果给启动它的活动,可以使用startActivityForResult(),并在目标活动中通过setResult()设置结果,然后在启动活动的onActivityResult()中接收结果。 以上是关于“Android:使用活动”的核心知识点,理解和实践这些内容将有助于你构建功能丰富且用户体验良好的Android应用程序。在实际开发中,还需要不断学习和适应Android的新特性与最佳实践。
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