Android Popupwindow 拖动

版本号：1.0

日期：2014.4.29

关于View的拖动大家应该比較了解了，比方对一个控件IamgeView拖动，或者一个视图View拖动，实现方式也非常easy，继承OnTouchListener接口，然后重写onTouch方法，在触屏事件进行处理就可以。可是Popupwindow怎样实现拖动呢，我们都知道它和普通的View不一样，由于它不是继承于View类的，可是它的实现却是和View密切相关的，由于我们都知道Android视图的显示都是由View来处理的，所以一定离不开它。从Popupwindow的实现就能够看出来，

import com.android.internal.R;

import android.content.Context;
import android.content.res.Resources;
import android.content.res.TypedArray;
import android.graphics.PixelFormat;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.StateListDrawable;
import android.os.Build;
import android.os.IBinder;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.view.ViewTreeObserver.OnScrollChangedListener;
import android.view.WindowManager;

import java.lang.ref.WeakReference;

上面是它的导包情况，基本上不是和View相关，就是和画图相关。因此关于Popupwindow的拖动这一块，也和View有联系。首先看一下它的API，看一看有没有和View移动、变化相关的方法，果然在最后有几个update()方法，例如以下：

update()方法用来更新Popupwindow的位置和大小的，那么问题就好攻克了。看代码：

package com.example.drag_and_drop_movablepopupwindow;

import android.support.v7.app.ActionBarActivity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.PopupWindow;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity {

	private Button btnOpenPopup;

	private int mCurrentX;
	private int mCurrentY;
	
	private PopupWindow mPopup;
	 
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		
		setContentView(R.layout.activity_main);
		btnOpenPopup = (Button) findViewById(R.id.openpopup);
		btnOpenPopup.setOnClickListener(new Button.OnClickListener() {

			@Override
			public void onClick(View arg0) {
				creatPopubWindow_1();
			}
		});
	}

	/**
	 * 1
	 */
	private void creatPopubWindow_1() {
		LayoutInflater layoutInflater = (LayoutInflater) getBaseContext()
				.getSystemService(LAYOUT_INFLATER_SERVICE);
		View popupView = layoutInflater.inflate(R.layout.popup, null);
		final PopupWindow popupWindow = new PopupWindow(popupView,
				200, 200);

		Button btnDismiss = (Button) popupView.findViewById(R.id.dismiss);
		btnDismiss.setOnClickListener(new Button.OnClickListener() {

			@Override
			public void onClick(View v) {
				popupWindow.dismiss();
			}
		});

		popupWindow.showAsDropDown(btnOpenPopup, 50, 50);

		popupView.setOnTouchListener(new OnTouchListener() {
			int orgX, orgY;
			int offsetX, offsetY;

			@Override
			public boolean onTouch(View v, MotionEvent event) {
				switch (event.getAction()) {
				case MotionEvent.ACTION_DOWN:
					orgX = (int) event.getX();
					orgY = (int) event.getY();
					break;
				case MotionEvent.ACTION_MOVE:
					offsetX = (int) event.getRawX() - orgX;
					offsetY = (int) event.getRawY() - orgY;
					popupWindow.update(offsetX, offsetY, -1, -1, true);
					break;
				}
				return true;
			}
		});
	}
}

效果如图：

首先对Popupwindow设置触摸事件，然后在回调方法中进行计算，假设手指拖动了Popupwindow，那么就调用update()方法来更新它的位置。有些同学可能不太理解參数-1是什么意思，在上面的API中，写明的是宽和高，这里怎么变成-1了呢，看一下Popupwindow源码就明确了。

 /**
     * <p>Updates the position and the dimension of the popup window. Width and
     * height can be set to -1 to update location only.  Calling this function
     * also updates the window with the current popup state as
     * described for {@link #update()}.</p>
     *
     * @param x the new x location
     * @param y the new y location
     * @param width the new width, can be -1 to ignore
     * @param height the new height, can be -1 to ignore
     * @param force reposition the window even if the specified position
     *              already seems to correspond to the LayoutParams
     */
    public void update(int x, int y, int width, int height, boolean force) {
        if (width != -1) {
            mLastWidth = width;
            setWidth(width);
        }

        if (height != -1) {
            mLastHeight = height;
            setHeight(height);
        }

        if (!isShowing() || mContentView == null) {
            return;
        }

        WindowManager.LayoutParams p = (WindowManager.LayoutParams) mPopupView.getLayoutParams();

        boolean update = force;

        final int finalWidth = mWidthMode < 0 ? mWidthMode : mLastWidth;
        if (width != -1 && p.width != finalWidth) {
            p.width = mLastWidth = finalWidth;
            update = true;
        }

        final int finalHeight = mHeightMode < 0 ? mHeightMode : mLastHeight;
        if (height != -1 && p.height != finalHeight) {
            p.height = mLastHeight = finalHeight;
            update = true;
        }

        if (p.x != x) {
            p.x = x;
            update = true;
        }

        if (p.y != y) {
            p.y = y;
            update = true;
        }

        final int newAnim = computeAnimationResource();
        if (newAnim != p.windowAnimations) {
            p.windowAnimations = newAnim;
            update = true;
        }

        final int newFlags = computeFlags(p.flags);
        if (newFlags != p.flags) {
            p.flags = newFlags;
            update = true;
        }

        if (update) {
            setLayoutDirectionFromAnchor();
            mWindowManager.updateViewLayout(mPopupView, p);
        }
    }

前两个if推断已经说得非常清楚了，假设參数是-1的话，就不改变Popupwindow的大小了，由于我们仅仅是移动位置，所以才这样写。那关于Popupwindow的移动最后是怎么实现的呢，能够看出就是调用WindowManager的updateViewLayout()方法，这种方法在WindowManager中并没有实现，它是ViewManager接口里面的方法，WindowManager继承了ViewManager。说到ViewManager，它里面定义的方法都非经常常使用，看代码：

/** Interface to let you add and remove child views to an Activity. To get an instance
  * of this class, call {@link android.content.Context#getSystemService(java.lang.String) Context.getSystemService()}.
  */
public interface ViewManager
{
    /**
     * Assign the passed LayoutParams to the passed View and add the view to the window.
     * <p>Throws {@link android.view.WindowManager.BadTokenException} for certain programming
     * errors, such as adding a second view to a window without removing the first view.
     * <p>Throws {@link android.view.WindowManager.InvalidDisplayException} if the window is on a
     * secondary {@link Display} and the specified display can't be found
     * (see {@link android.app.Presentation}).
     * @param view The view to be added to this window.
     * @param params The LayoutParams to assign to view.
     */
    public void addView(View view, ViewGroup.LayoutParams params);
    public void updateViewLayout(View view, ViewGroup.LayoutParams params);
    public void removeView(View view);
}

这下大家应该明了，我们经经常使用的addView、removeView方法就是在这里面定义的，那么谁去实现呢？就是Layout控件，比方LinearLayout、RelativeLayout等，所以我们刚才用的updateViewLayout()方法也是在xml布局文件里的layout定义好的。