android之OnTouchListener只能监听到ACTION_DOWN—–onTouchListener的返回值问题「建议收藏」

大家好，又见面了，我是全栈君。

做这样一个效果，界面上显示一个紫色方块，任意拖动方块到指定位置都可以，

运行后结果发现方块怎么都拖不动，打印log只有ACTION_DOWN有反应，MOVE和UP都监听不到，

很是奇怪，先把整段代码都贴下面了

package jason.com.security.ui;

import jason.com.security.R;
import android.app.Activity;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.Window;
import android.widget.ImageView;
import android.widget.RelativeLayout;
import android.widget.RelativeLayout.LayoutParams;

public class DragViewActivity extends Activity implements OnTouchListener {

	String TAG = "DragViewActivity";

	void log(String s) {
		Log.d(TAG, s);
	}

	private ImageView iv_drag_location;
	private SharedPreferences sp;

	int startX;
	int startY;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		requestWindowFeature(Window.FEATURE_NO_TITLE);
		setContentView(R.layout.drag_view);

		sp = getSharedPreferences("config", MODE_PRIVATE);

		iv_drag_location = (ImageView) findViewById(R.id.iv_drag_location);
		iv_drag_location.setOnTouchListener(this);

	}

	@Override
	protected void onResume() {
		// TODO Auto-generated method stub
		super.onResume();
		int x = sp.getInt("lastX", 0);
		int y = sp.getInt("lastY", 0);
		log("last X is " + x + ",lastY is " + y);
		RelativeLayout.LayoutParams params = (LayoutParams) iv_drag_location
				.getLayoutParams();
		params.leftMargin = x;
		params.topMargin = y;
		iv_drag_location.setLayoutParams(params);
	}

	@Override
	public boolean onTouch(View v, MotionEvent event) {
		// TODO Auto-generated method stub

		switch (v.getId()) {
		case R.id.iv_drag_location:
			switch (event.getAction()) {
			case MotionEvent.ACTION_DOWN:
				startX = (int) event.getRawX();
				startY = (int) event.getRawY();
				log("ACTION_DOWN :" + startX + "-" + startY);
				break;

			case MotionEvent.ACTION_MOVE:
				int dx = (int) (event.getRawX() - startX);
				int dy = (int) (event.getRawY() - startY);
				log("ACTION_MOVE :" + dx + "-" + dy);
				int l = iv_drag_location.getLeft();
				int r = iv_drag_location.getRight();
				int t = iv_drag_location.getTop();
				int b = iv_drag_location.getBottom();
				iv_drag_location.layout(l + dx, t + dy, r + dx, b + dy);
				startX = (int) event.getRawX();
				startY = (int) event.getRawY();
				break;

			case MotionEvent.ACTION_UP:
				int lastX = iv_drag_location.getLeft();
				int lastY = iv_drag_location.getTop();
				log("ACTION_UP :" + lastX + "-" + lastY);
				Editor editor = sp.edit();
				editor.putInt("lastX", lastX);
				editor.putInt("lastY", lastY);
				editor.commit();
				break;

			default:
				break;
			}
			break;

		default:
			break;
		}

		return false;
	}

}

检查了N遍，逻辑上实在没问题，

最后发现，最后的返回值是return false;

由于这个是编译器自动生成的，我也没改动过，就改成了return true试试

果然，就是这个的问题，改成return true之后就正常了，

文档中对该方法的返回值描述如下：True if the listener has consumed the event, false otherwise。

大概意思就是说，如果返回true，则表示监听器处理了该事件(我的理解就是不用继续向上传递该事件了，该事件的传递到此为止)；

否则返回false。

这样一想，我觉得之前返回false，可能造成之后检测到的事件向上传递了，而没有在该监听函数中处理。

所以导致了错误。

作者：jason0539

微博：http://weibo.com/2553717707

博客：http://blog.csdn.net/jason0539（转载请说明出处）