<!-- [if !mso]> <style> v/:* {behavior:url(#default#VML);} o/:* {behavior:url(#default#VML);} w/:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} </style> <![endif]--><!-- [if gte mso 9]><xml> <o:OfficeDocumentSettings> <o:RelyOnVML/> <o:AllowPNG/> </o:OfficeDocumentSettings> </xml><![endif]--><!-- [if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:TrackMoves>false</w:TrackMoves> <w:TrackFormatting/> <w:PunctuationKerning/> <w:DrawingGridVerticalSpacing>7.8 磅</w:DrawingGridVerticalSpacing> <w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery> <w:DisplayVerticalDrawingGridEvery>2</w:DisplayVerticalDrawingGridEvery> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:DoNotPromoteQF/> <w:LidThemeOther>EN-US</w:LidThemeOther> <w:LidThemeAsian>ZH-CN</w:LidThemeAsian> 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ImageSwitcher 是 ViewGroup 的派生类, ViewGroup 是 View 的派生类。
ImageSwitcher 很简单见,但在使用它的时候,有一个地方必须要注意,否则就会出现 NullPointerException 。具体情况,请见下面的例子。
在这个例子中,我们将大致要重复做一遍 AndroidGUI19 : Gallery 常用技巧中的提到的事情。也就是说,这次我们还要用到 Gallery ,不过这次不再用 ImageView 来显示大图了,而是改用 ImageSwitcher 来代替它。
1. 创建一个 Android Project ,修改 main.xml 使之如下:
<? xml version = "1.0" encoding = "utf-8" ?>
< RelativeLayout xmlns:android = "http://schemas.android.com/apk/res/android"
android:orientation = "vertical"
android:layout_width = "fill_parent"
android:layout_height = "fill_parent"
>
< ImageSwitcher
android:id = "@+id/imageswitcher"
android:layout_width = "match_parent"
android:layout_height = "wrap_content"
android:layout_alignParentTop = "true"
/>
< Gallery
android:id = "@+id/gallery"
android:layout_width = "fill_parent"
android:layout_height = "wrap_content"
android:gravity = "center_vertical"
android:spacing = "10px"
android:layout_marginTop = "10px"
android:layout_alignParentBottom = "true"
/>
<!--
android:layout_alignParentBottom="true"
就是让 Gallery 位于屏幕底端, LinearLayout 不存在这个属性
-->
</ RelativeLayout >
2. 把项目需要用到的图片文件拖入 res/drawable-mdpi 文件夹下,如下图所示
3. 实现一个自定义的 Adapter: ImageAdapter ,代码如下:
package com.pat.gui;
import android.content.Context;
import android.graphics.Color;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
public class ImageAdapter extends BaseAdapter
{
private Context ctx;
private int images[] =
{
R.drawable.lrt01,
R.drawable.lrt02,
R.drawable.lrt03,
R.drawable.lrt04,
R.drawable.lrt05,
R.drawable.lrt06,
R.drawable.lrt07,
R.drawable.lrt08,
R.drawable.lrt09
};
public ImageAdapter(Context ctx)
{
this.ctx = ctx;
}
//@Override
public int getCount()
{
return images.length;
}
//@Override
public Object getItem(int position)
{
return images[position];
}
//@Override
public long getItemId(int position)
{
return images[position];
}
//@Override
public View getView(int position, View convertView, ViewGroup parent)
{
ImageView view;
view = (ImageView)convertView;
if(view == null)
{
view = new ImageView(ctx);
}
view.setImageResource(images[position]);
view.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
view.setLayoutParams(new Gallery.LayoutParams(60, 60));
view.setBackgroundColor(Color.LTGRAY);
return view;
}
}
4. 实现 Activity 所对应的代码,使之如下 ( 注意其中的粗体字部分 ) :
package com.pat.gui;
import android.app.Activity;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;
import android.widget.AdapterView;
import android.widget.Gallery;
import android.widget.ImageSwitcher;
import android.widget.ImageView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.FrameLayout.LayoutParams;
import android.widget.ViewSwitcher.ViewFactory;
public class ControlImageSwitcher extends Activity
implements
OnItemSelectedListener, ViewFactory
{
private Gallery gallery;
private ImageSwitcher imageswitcher;
private ImageAdapter adapter;
private DisplayMetrics dm;
//@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);// 隐藏标题
int flag = WindowManager.LayoutParams.FLAG_FULLSCREEN; // 全屏
this.getWindow().setFlags(flag, flag);
setContentView(R.layout.main);
// 得到屏幕尺寸
dm = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(dm);
gallery = (Gallery)this.findViewById(R.id.gallery);
imageswitcher = (ImageSwitcher)this.findViewById(R.id.imageswitcher);
// 下面这句必须要,不然会使 setImageSource 这个方法指向空指针
imageswitcher.setFactory(this);
adapter = new ImageAdapter(this);
gallery.setAdapter(adapter);
gallery.setOnItemSelectedListener(this);
}
//@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id)
{
int imageID = (int) adapter.getItemId(position);
imageswitcher.setImageResource(imageID);
}
//@Override
public void onNothingSelected(AdapterView<?> parent)
{
imageswitcher.setImageResource((int) adapter.getItemId(0));
}
//@Override
// 接口 ViewFactory 中规定必须实现的方法,返回的 View 就是 ImageSwitcher 用于显示图片的 vie w
public View makeView()
{
ImageView iv = new ImageView(this);
// 设置背景颜色
iv.setBackgroundColor(0xFF646464);
iv.setScaleType(ImageView.ScaleType.FIT_CENTER);
iv.setLayoutParams(new ImageSwitcher.LayoutParams(LayoutParams.FILL_PARENT, dm.heightPixels - 70));
// 上面语句中 -70 的目的是应为, ImageSwitcher 下面要显示 Gallery ,我们在 ImageAdapter 中设定了
// view.setLayoutParams(new Gallery.LayoutParams(60, 60));
// 即高度是 60pixels ,在加在 main.xml 中 Gallery 有下面这样的属性:
// android:layout_marginTop="10px"
// 因此加起来一共刚好是 70px
return iv;
}
}
运行结果:
让下面的 Gallery 中的图片滚动,上面的 ImageSwitcher 会显示 Gallery 在屏幕上处于中间 ( 水平方向 ) 位置的那副图片: