Android 回调机制
16lz
2021-01-23
Android 回调机制
在android开发中经常遇到各种各样的回调方法，然而，到底什么是回调呢？
现在，以android中View的onClick()回调方法为例，讲解一下。
OnClickListener 接口，当view被点击后回调该接口
/** * Interface definition for a callback to be invoked when a view is clicked. */ public interface OnClickListener { /** * Called when a view has been clicked. * * @param v The view that was clicked. */ void onClick(View v); }在Activity中实现回调接口
public class MainActivity extends Activity implements OnClickListener { Button btn_location; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); btn_location = (Button) findViewById(R.id.btn_location); btn_location.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { //TODO action } }); }}View 类 当View被点击后，注册一个回调接口，用于调用。
public class View implements Drawable.Callback, KeyEvent.Callback, AccessibilityEventSource { /** * Listener used to dispatch click events. * This field should be made private, so it is hidden from the SDK. * {@hide} */ public OnClickListener mOnClickListener; /** * Register a callback to be invoked when this view is clicked. If this view is not * clickable, it becomes clickable. * * @param l The callback that will run * * @see #setClickable(boolean) */ public void setOnClickListener(OnClickListener l) { if (!isClickable()) { setClickable(true); } getListenerInfo().mOnClickListener = l; } /** * Call this view's OnClickListener, if it is defined. Performs all normal * actions associated with clicking: reporting accessibility event, playing * a sound, etc. * * @return True there was an assigned OnClickListener that was called, false * otherwise is returned. */ public boolean performClick() { sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED); ListenerInfo li = mListenerInfo; if (li != null && li.mOnClickListener != null) { playSoundEffect(SoundEffectConstants.CLICK); li.mOnClickListener.onClick(this); return true; } return false; }}更多相关文章
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