Android课程---用进度条改变图片透明度

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context="com.hanqi.test5.UIActivity2">
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="长按触发上下文菜单"
        android:id="@+id/bt_changan"/>
    <ProgressBar
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/pb_1"/>
    <ProgressBar
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        style="?android:attr/progressBarStyleHorizontal"
        android:max="100"
        android:progress="50"
        android:secondaryProgress="70"
        android:id="@+id/pb_2" />
   <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/vipflower"
        android:id="@+id/iv_vip"/>
    <SeekBar
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:max="100"
        android:progress="100"
        android:id="@+id/sb_1"/><!--可拖动-->

</LinearLayout>

package com.hanqi.test5;

import android.app.Activity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.SubMenu;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.SeekBar;
import android.widget.Toast;

public class UIActivity2 extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_ui2);
        Button bt_changan = (Button)findViewById(R.id.bt_changan);
        bt_changan.setOnCreateContextMenuListener(this);/*this代表当前Activity,实现了这个接口*/

        //进度条
        //有final时，生命周期长，不加final的话就只是当前方法的，加final可以延长生命周期，或者定义成员变量
        final ProgressBar pb_1 =(ProgressBar)findViewById(R.id.pb_1);
        final ProgressBar pb_2 =(ProgressBar)findViewById(R.id.pb_2);
        final SeekBar sb_1 =(SeekBar)findViewById(R.id.sb_1);

        sb_1.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            //onProgressChanged进度条变化,进度改变就会触发
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                //pb_2.setProgress(seekBar.getProgress());
                ImageView iv_vip = (ImageView)findViewById(R.id.iv_vip);
                //iv_vip.setAlpha(0.2f);透明度值是0-255
                iv_vip.setImageAlpha(progress * 255 /100);
            }

            //onStartTrackingTouch开始拖动
            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            //onStopTrackingTouch停止拖动
            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {
                pb_2.setProgress(seekBar.getProgress());

                if (seekBar.getProgress() == seekBar.getMax())
                {
                    //设置不可见
                    pb_1.setVisibility(View.GONE);
                    /*INVISIBLE不可见（占空间） VISIBLE可见 GONE不可见（不占空间）*/
                }
                else
                {
                    pb_1.setVisibility(View.VISIBLE);
                }

            }
        });

    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
        menu.add(0,1,0,"添加");
        menu.add(0,2,1,"修改");
        menu.add(0, 3, 2, "删除");
        SubMenu m = menu.addSubMenu(0, 4, 3, "子菜单");

        m.add(0,41,0,"子菜单项1");
        m.add(0,42,1,"子菜单项2");
        m.add(0,43,2,"子菜单项3");
        m.add(0,44,3,"子菜单项4");
//        MenuInflater mi =getMenuInflater();
//        mi.inflate(R.menu.mymenu,menu);
        super.onCreateContextMenu(menu, v, menuInfo);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        switch (item.getItemId())
        {
            case R.id.it_2:
                Toast.makeText(UIActivity2.this, "触发了添加1功能", Toast.LENGTH_SHORT).show();
                break;
            case R.id.it_1:
                Toast.makeText(UIActivity2.this, "触发了删除1功能", Toast.LENGTH_SHORT).show();
                break;
        }
        return super.onContextItemSelected(item);
    }

    @Override
    //重写  创建选项菜单的方法
    public boolean onCreateOptionsMenu(Menu menu) {

        //添加菜单项
        //纯编码方式
//        menu.add(0,1,0,"添加");
//        menu.add(0,2,2,"删除");
//        menu.add(0,3,1,"修改");

        //加载菜单文件方式
        //1.获取菜单加载器
        MenuInflater mi =getMenuInflater();
        mi.inflate(R.menu.mymenu,menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        //Toast.makeText(UIActivity2.this, "选中的菜单项是" + item.getTitle(), Toast.LENGTH_SHORT).show();
        //根据菜单项的不同响应不同功能
        switch (item.getItemId())
        {
            case 1:
                Toast.makeText(UIActivity2.this, "触发了添加功能", Toast.LENGTH_SHORT).show();
                break;
            case 2:
                Toast.makeText(UIActivity2.this, "触发了删除功能", Toast.LENGTH_SHORT).show();
                break;
            case 3:
                Toast.makeText(UIActivity2.this, "触发了修改功能", Toast.LENGTH_SHORT).show();
                break;
            case R.id.it_2:
                Toast.makeText(UIActivity2.this, "触发了添加1功能", Toast.LENGTH_SHORT).show();
                break;
            case R.id.it_1:
                Toast.makeText(UIActivity2.this, "触发了删除1功能", Toast.LENGTH_SHORT).show();
                break;
        }

        return super.onOptionsItemSelected(item);
    }
}

效果图：