Android控件之ImageView探究

ImageView控件是一个图片控件，负责显示图片。

以下模拟手机图片查看器

目录结构

main.xml布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <ImageView android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:src="@drawable/p1"/>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="horizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal">
        <Button android:id="@+id/previous"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="上一张"
            android:layout_gravity="center_horizontal"/>
        <Button android:id="@+id/alpha_plus"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="透明度增加"
            android:layout_gravity="center_horizontal"/>
        <Button android:id="@+id/alpha_minus"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="透明度减少"
            android:layout_gravity="center_horizontal"/>
        <Button android:id="@+id/next"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="下一张"
            android:layout_gravity="center_horizontal"/>
    </LinearLayout>
</LinearLayout>

ImageViewActivity类

package com.ljq.iv;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class ImageViewActivity extends Activity {
    private ImageView imageView=null;
    private Button previous=null;//上一张
    private Button next=null;//下一张
    private Button alpha_plus=null;//透明度增加
    private Button alpha_minus=null;//透明度减少
    private int currentImgId=0;//记录当前ImageView显示的图片id
    private int alpha=255;//记录ImageView的透明度
    int [] imgId = {            //ImageView显示的图片数组
            R.drawable.p1,    
            R.drawable.p2,
            R.drawable.p3,
            R.drawable.p4,
            R.drawable.p5,
            R.drawable.p6,
            R.drawable.p7,
            R.drawable.p8,
        };
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        imageView=(ImageView)findViewById(R.id.imageView);
        previous=(Button)findViewById(R.id.previous);
        next=(Button)findViewById(R.id.next);
        alpha_plus=(Button)findViewById(R.id.alpha_plus);
        alpha_minus=(Button)findViewById(R.id.alpha_minus);
       
        previous.setOnClickListener(listener);
        next.setOnClickListener(listener);
        alpha_plus.setOnClickListener(listener);
        alpha_minus.setOnClickListener(listener);
    }
    
    private View.OnClickListener listener = new View.OnClickListener(){

        public void onClick(View v) {
            if(v==previous){
                currentImgId=(currentImgId-1+imgId.length)%imgId.length;
                imageView.setImageResource(imgId[currentImgId]);
            }
            if(v==next){
                currentImgId=(currentImgId+1)%imgId.length;
                imageView.setImageResource(imgId[currentImgId]);
            }
            if(v==alpha_plus){
                alpha+=10;
                if(alpha>255){
                    alpha=255;
                }
                imageView.setAlpha(alpha);
            }
            if(v==alpha_minus){
                alpha-=10;
                if(alpha<0){
                    alpha=0;
                }
                imageView.setAlpha(alpha);
            }
        }
        
    };
    
}

运行结果