在Android开发中，需要用到PopupWindow这个类。在初始化完成，显示之前，都需要获得这个对象的width，height去计算popupWindow弹出的位置。
这个时候会发现取得的width和height都是-2；使用popupWindow.getContentView().getMeasuredWidth()和popupWindow.getContentView().getMeasuredHeight()取得的值都是0。如下面的代码：
activity_main.xml
1 <?xml version="1.0" encoding="utf-8"?> 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 3 android:orientation="vertical" 4 android:layout_width="fill_parent" 5 android:layout_height="fill_parent" 6 > 7 8 <Button 9 android:layout_width="wrap_content" 10 android:layout_height="wrap_content" 11 android:text="New Button" 12 android:id="@+id/button" 13 android:layout_gravity="center_horizontal"/> 14 </LinearLayout>
popwin_layout.xml
1 <?xml version="1.0" encoding="utf-8"?> 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 3 android:orientation="vertical" 4 android:layout_width="match_parent" 5 android:layout_height="match_parent"> 6 <ImageView 7 android:layout_width="wrap_content" 8 android:layout_height="wrap_content" 9 android:src="@drawable/ic_launcher"/> 10 </LinearLayout>
MyActivity.class
1 package com.example.popwinsize;
2
3 import android.app.Activity;
4 import android.graphics.drawable.BitmapDrawable;
5 import android.os.Bundle;
6 import android.text.Layout;
7 import android.util.Log;
8 import android.view.LayoutInflater;
9 import android.view.View;
10 import android.view.ViewGroup;
11 import android.widget.Button;
12 import android.widget.PopupWindow;
13
14 public class MyActivity extends Activity {
15
16 private PopupWindow mPopWin;
17
18 private Button mButton;
19
20 /**
21 * Called when the activity is first created.
22 */
23 @Override
24 public void onCreate(Bundle savedInstanceState) {
25 super.onCreate(savedInstanceState);
26 setContentView(R.layout.activity_main);
27 mButton = (Button) findViewById(R.id.button);
28 mButton.setOnClickListener(new ButtonClickListener());
29
30 initPopupWindow();
31 }
32
33 /**
34 * 初始化PopupWindow
35 */
36 private void initPopupWindow() {
37 View contentView = LayoutInflater.from(this).inflate(R.layout.popwin_layout, null);
38 mPopWin = new PopupWindow(contentView,
39 ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
40 mPopWin.setBackgroundDrawable(new BitmapDrawable()); //设置背景，否则setOutsideTouchable无效
41 mPopWin.setOutsideTouchable(true); //设置点击PopupWindow以外的地方关闭PopupWindow
42 mPopWin.setFocusable(true); //获取焦点
43 }
44
45 class ButtonClickListener implements View.OnClickListener {
46
47 @Override
48 public void onClick(View v) {
49 //点击在按钮的中下方弹出mPopWin
50
51 int btnWidth = v.getMeasuredWidth();
52 int btnHeight = v.getMeasuredHeight();
53
54 int popWidth = mPopWin.getContentView().getMeasuredWidth();
55 int popHeight = mPopWin.getContentView().getMeasuredHeight();
56 Log.i("Button.size", "width=" + btnWidth + "; height=" + btnHeight);
57 Log.i("PopupWindow.size", "width=" + popWidth + "; height=" + popHeight);
58 //mPopWin.showAsDropDown(v); //这个是在按钮的下方出现，x值与按钮的x值相等
59
60 int xoff = (int)((float)(btnWidth - popWidth)/2); //PopupWindow的x偏移值
61 int yoff = 0; //因为相对于按钮的下方，所以该值为0
62
63 mPopWin.showAsDropDown(v, xoff, yoff);
64 }
65 }
66 }
这个时候你会发现，出现的效果并不是您想要的效果，是在按钮是右下方出现
LogCat捕获的结果是：
I/Button.size﹕ width=176; height=72
I/PopupWindow.size﹕ width=0; height=0
出现这个的原因就是因为PopupWindow的尺寸拿不到，因为内容的View的width和height都是wrap_content，所以在PopupWindow里面的contentView还没被绘制出来的时候，这两个值都还是0。
如果直接调用PopupWindow的getWidth()和getHeight()，会发现拿到的都是ViewGroup.LayoutParams.WRAP_CONTENT的值 -2;
解决的方法就是在初始化contentView的时候，强制绘制contentView，并且马上初始化contentView的尺寸。这里只需要一句代码即可
看下面的MyActivity.class的第38行代码：
1 package com.example.popwinsize;
2
3 import android.app.Activity;
4 import android.graphics.drawable.BitmapDrawable;
5 import android.os.Bundle;
6 import android.text.Layout;
7 import android.util.Log;
8 import android.view.LayoutInflater;
9 import android.view.View;
10 import android.view.ViewGroup;
11 import android.widget.Button;
12 import android.widget.PopupWindow;
13
14 public class MyActivity extends Activity {
15
16 private PopupWindow mPopWin;
17
18 private Button mButton;
19
20 /**
21 * Called when the activity is first created.
22 */
23 @Override
24 public void onCreate(Bundle savedInstanceState) {
25 super.onCreate(savedInstanceState);
26 setContentView(R.layout.activity_main);
27 mButton = (Button) findViewById(R.id.button);
28 mButton.setOnClickListener(new ButtonClickListener());
29
30 initPopupWindow();
31 }
32
33 /**
34 * 初始化PopupWindow
35 */
36 private void initPopupWindow() {
37 View contentView = LayoutInflater.from(this).inflate(R.layout.popwin_layout, null);
38 contentView.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);
39 mPopWin = new PopupWindow(contentView,
40 ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
41 mPopWin.setBackgroundDrawable(new BitmapDrawable()); //设置背景，否则setOutsideTouchable无效
42 mPopWin.setOutsideTouchable(true); //设置点击PopupWindow以外的地方关闭PopupWindow
43 mPopWin.setFocusable(true); //获取焦点
44 }
45
46 class ButtonClickListener implements View.OnClickListener {
47
48 @Override
49 public void onClick(View v) {
50 //点击在按钮的中下方弹出mPopWin
51
52 int btnWidth = v.getMeasuredWidth();
53 int btnHeight = v.getMeasuredHeight();
54
55 int popWidth = mPopWin.getContentView().getMeasuredWidth();
56 int popHeight = mPopWin.getContentView().getMeasuredHeight();
57 Log.i("Button.size", "width=" + btnWidth + "; height=" + btnHeight);
58 Log.i("PopupWindow.size", "width=" + popWidth + "; height=" + popHeight);
59 //mPopWin.showAsDropDown(v); //在按钮的下方出现，x值与按钮的x值相等
60
61 int xoff = (int)((float)(btnWidth - popWidth)/2); //PopupWindow的x偏移值
62 int yoff = 0; //因为相对于按钮的下方，所以该值为0
63
64 mPopWin.showAsDropDown(v, xoff, yoff);
65 }
66 }
67 }
这个时候LogCat打印出来的结果：
I/Button.size﹕ width=176; height=72
I/PopupWindow.size﹕ width=72; height=72
效果如下：
另外一个点需要注意：popwin_layout.xml的根Layout必须为LinearLayout；如果为RelativeLayout的话，会在第38行代码出现空指针错误，导致程序崩溃。希望看到此文章的人在开发中需要注意。
转载于:https://www.cnblogs.com/gumf/p/4148863.html