Android基础巩固
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- Android基础学习笔记
- 复杂控件学习记录
- 参考《第一行代码(第二版)》、GoogleDeveloper等
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Context
- Context是维持Android程序中各组件能够正常工作的一个核心功能类。
- 弹出Toast、启动Activity、启动Service、发送广播、操作数据库等等都需要用到Context。
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TextView tv = new TextView(getContext()); ListAdapter adapter = new SimpleCursorAdapter(getApplicationContext(), ...); AudioManager am = (AudioManager) getContext().getSystemService(Context.AUDIO_SERVICE);getApplicationContext().getSharedPreferences(name, mode); getApplicationContext().getContentResolver().query(uri, ...); getContext().getResources().getDisplayMetrics().widthPixels * 5 / 8; getContext().startActivity(intent); getContext().startService(intent); getContext().sendBroadcast(intent);
Bundle savedInstanceState
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onCreate方法的完整定义如下:
public void onCreate(Bundle savedInstanceState){ super.onCreate(savedInstanceState); }
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从上面的代码可以看出,onCreate方法的参数是一个Bundle类型的参数。Bundle类型的数据与Map类型的数据相似,都是以key-value的形式存储数据的。
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从字面上看savedInstanceState,是保存实例状态的。实际上,savedInstanceState也就是保存Activity的状态的
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eg. SnakeView in SnakeGame :
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private int[] coordArrayListToArray(ArrayListcvec) { int count = cvec.size(); int[] rawArray = new int[count * 2]; for (int index = 0; index < count; index++) { Coordinate c = cvec.get(index); rawArray[2 * index] = c.x; rawArray[2 * index + 1] = c.y; } return rawArray; } public Bundle saveState() { Bundle map = new Bundle(); map.putIntArray("mAppleList", coordArrayListToArray(mAppleList)); map.putInt("mDirection", Integer.valueOf(mDirection)); map.putInt("mNextDirection", Integer.valueOf(mNextDirection)); map.putLong("mMoveDelay", Long.valueOf(mMoveDelay)); map.putLong("mScore", Long.valueOf(mScore)); map.putIntArray("mSnakeTrail", coordArrayListToArray(mSnakeTrail)); return map; } 在snakeActivity中实现 @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.snake_layout); mSnakeView = (SnakeView) findViewById(R.id.snake); mSnakeView.setTextView((TextView) findViewById(R.id.text)); if (savedInstanceState == null) { // We were just launched -- set up a new game mSnakeView.setMode(SnakeView.READY); } else { // We are being restored Bundle map = savedInstanceState.getBundle(ICICLE_KEY); if (map != null) { mSnakeView.restoreState(map); } else { mSnakeView.setMode(SnakeView.PAUSE); } } } 并重写onSavedInstanceState(),此方法会在activity结束时,调用. @Override public void onSaveInstanceState(Bundle outState) { //Store the game state outState.putBundle(ICICLE_KEY, mSnakeView.saveState()); }