Android Popupwindow弹出窗口的简单使用方法

import android.content.Context;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup.LayoutParams;import android.widget.Button;import android.widget.PopupWindow;import android.widget.Toast;public class MainActivity extends AppCompatActivity {  private Context mContext = null;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    mContext = this;    Button button = (Button) findViewById(R.id.but);    button.setOnClickListener(newView.OnClickListener() {      @Override      public void onClick(View view) {        showPopupWindow(view);      }    });  }  private void showPopupWindow(View view) {    // 一个自定义的布局，作为显示的内容    View contentView =LayoutInflater.from(mContext).inflate(        R.layout.popupwindow, null);    // 设置按钮的点击事件    Button button = (Button) contentView.findViewById(R.id.button );      button.setOnClickListener(new View.OnClickListener() {          @Override          public void onClick(View v) {            Toast.makeText(mContext, "button is pressed",                Toast.LENGTH_SHORT).show();          }    });    final PopupWindow popupWindow = new PopupWindow(contentView,  LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT, true);    // 如果不设置PopupWindow的背景，无论是点击外部区域还是Back键都无法dismiss弹框    // 我觉得这里是API的一个bug    popupWindow.setBackgroundDrawable(getResources().getDrawable(R.mipmap.ic_launcher));    // 设置好参数之后再show    popupWindow.showAsDropDown(view);  }}

 <Button    android:id="@+id/but"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="Hello World!" />

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  android:orientation="vertical" android:layout_width="match_parent"  android:layout_height="match_parent"  android:background="#ffff00"><TextView  android:id="@+id/ttt"  android:layout_width="wrap_content"  android:layout_height="wrap_content"  android:textSize="20sp"  android:text="弹出窗口"/>  <Button    android:id="@+id/button"    android:layout_width="wrap_content"    android:layout_height="wrap_content" /></LinearLayout>