一、ViewPager簡單介紹
素材和參考文章:http://blog.csdn.net/xiaanming/article/details/8966621
ViewPager在應用中使用的非常廣泛,也是一個AdapterView在使用在需要使用適配器PagerAdapter。ViewPager在更新的時候使用了回調刪除的機制。ViewPager將每一個頁面與一個關鍵對象Object相關聯,而不是直接使用其中的view對象;一般簡單實現時,使用page Views作爲關鍵對象key Object,從instantiateItem方法中返回的值。
在實現PagerAdapter適配器時都有重現其中的四個方法:
instantiateItem(ViewGroup, int)
destroyItem(ViewGroup, int, Object)
getCount()
isViewFromObject(View, Object)
3張圖片循環報錯的情況:
所以但我們只有3張圖片時要實現循環滾動,如果一直是向左邊滑動這是沒有問題的。但是如果向右滑動查看前面一張圖片的時候會報錯。java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.因爲這時要先添加後刪除,但是添加上去的view這時已經是有parent的。所以我們需要先進行手動刪除,詳細見代碼部分。如果只有兩張的情況下,繼續使用這種方法會先出現空白在出圖片,效果不好。只有兩張,建議去掉循環功能;
/**
* 素材和參考文章:http://blog.csdn.net/xiaanming/article/details/8966621
* 官網上的viewPage類介紹:http://developer.android.com/reference/android/support/v4/view/ViewPager.html
* PagerAdapter:http://developer.android.com/reference/android/support/v4/view/PagerAdapter.html
*/
import com.sjc.myproject.R;
import android.app.Activity;
import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.LinearLayout.LayoutParams;
public class SjcViewPageActivity extends Activity implements OnPageChangeListener{
private ViewPager viewPage;
// 裝ImageView數組
private ImageView[] mImageViews;
// 圖片資源id
private int[] imgIdArray ;
//圖片位置提示
private ImageView[] tips;
private int currentSelectedIndex;
private LinearLayout viewGroup;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_viewpage);
initData();
viewPage = (ViewPager) findViewById(R.id.viewpage);
viewGroup = (LinearLayout) findViewById(R.id.viewGroup);
setIndicator();
viewPage.setAdapter(new MyAdapter());
viewPage.setOnPageChangeListener(this);
}
private void initData() {
currentSelectedIndex = 0;
imgIdArray = new int[]{R.drawable.item01, R.drawable.item02, R.drawable.item03,
R.drawable.item04, R.drawable.item05, R.drawable.item06, R.drawable.item07, R.drawable.item08};
mImageViews = new ImageView[imgIdArray.length];
for(int i=0, length = imgIdArray.length; i<length; i++) {
ImageView imageView = new ImageView(this);
imageView.setBackgroundResource(imgIdArray[i]);
mImageViews[i] = imageView;
}
tips = new ImageView[imgIdArray.length];
for(int i=0, length = imgIdArray.length; i<length; i++) {
ImageView imageView = new ImageView(this);
tips[i] = imageView;
if(i == currentSelectedIndex){
tips[i].setBackgroundResource(R.drawable.page_indicator_focused);
}else{
tips[i].setBackgroundResource(R.drawable.page_indicator_unfocused);
}
}
}
//設置位置指示
private void setIndicator() {
LayoutParams layoutParams = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
layoutParams.leftMargin = 10;
layoutParams.rightMargin = 10;
for(int i =0, length = tips.length; i<length; i++) {
viewGroup.addView(tips[i], layoutParams);
}
}
private void exchangeIndecator(int selecteIndex) {
tips[currentSelectedIndex].setBackgroundResource(R.drawable.page_indicator_unfocused);
tips[selecteIndex].setBackgroundResource(R.drawable.page_indicator_focused);
currentSelectedIndex = selecteIndex;
}
//PagerAdapter=============================
class MyAdapter extends PagerAdapter{
//返回ViewPager可以顯示的總數,如果大於這個數,這ViewPager不會調用相關的方法進行顯示,
//會多次調用,
//一般如果不需要進行界面的循環顯示,則返回實際的顯示數量如:return imgIdArray.length;就不會出現從最後一張返回第一張的功能。
public int getCount() {
//Log.d("TAG", "MyAdapter --> getCount");
if(mImageViews.length <= 2) {
return mImageViews.length;
}
return Integer.MAX_VALUE;
}
//用來確定一個界面是否於instantiateItem()返回的key Object相關聯
//只有返回值爲true時,纔會顯示界面
public boolean isViewFromObject(View arg0, Object arg1) {
//Log.v("TAG", "MyAdapter --> isViewFromObject");
return arg0 == arg1;
}
//刪除view page界面
//container 包含viewpage 的容器
//position:需要刪除的viewpage 的位置
//object:從instantiateItem(View container, int position)返回的對象
public void destroyItem(View container, int position, Object object) {
if(mImageViews.length > 3) {
Log.e("TAG", "MyAdapter --> destroyItem position = " + position% mImageViews.length);
//爲了你能循環顯示mImageViews[position % mImageViews.length]
((ViewPager)container).removeView(mImageViews[position % mImageViews.length]);
}
}
//爲給定的位置創建viewpage
public Object instantiateItem(View container, int position) {
Log.i("TAG", "MyAdapter --> instantiateItem position = " + position% mImageViews.length);
if(mImageViews[position % mImageViews.length].getParent() != null) {
((ViewPager)container).removeView(mImageViews[position % mImageViews.length]);
}
((ViewPager)container).addView(mImageViews[position % mImageViews.length], 0);
return mImageViews[position % mImageViews.length];
}
}
//OnPageChangeListener============
//滾動狀態發生改變時會調用此方法
//參數state:代表滾動的狀態;
//有三個常量來定義滾動狀態: SCROLL_STATE_IDLE 0、SCROLL_STATE_DRAGGING 1、SCROLL_STATE_SETTLING 2
//0:無滾動閒置狀態
//1:用戶正在開始拖拽界面
//2:界面正在進行調整其已經確定的最終位置
public void onPageScrollStateChanged(int state) {
//Log.i("TAG", "onPageScrollStateChanged --> state = " + state);
}
//初始化的時候會調用一次,ViewPager有滾動時調用
//position:當前顯示界面的index,position+1將會是下一個要顯示的界面
//positionOffset:取值範圍[0,1),說明當前頁面位置的偏移,相對於左下標點,往左滾動時數值增到,到達1時,界面換成下一個。
//positionOffsetPixels:像素值指示位置的偏移量,相對於右下標點
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
//Log.v("TAG", "onPageScrolled --> position = " + position + ", positionOffset = " + positionOffset + ", positionOffsetPixels = " + positionOffsetPixels);
}
//新界面被選定時調用此方法
//position:當前被選中界面的index
public void onPageSelected(int position) {
//Log.w("TAG", "onPageSelected --> arg0 = " + position);
exchangeIndecator(position % imgIdArray.length);
}
}
佈局文件activity_viewpage.xml:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<android.support.v4.view.ViewPager
android:id="@+id/viewpage"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<LinearLayout
android:id="@+id/viewGroup"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_gravity="bottom"
android:paddingBottom="30dp"
android:gravity="center_horizontal"
>
</LinearLayout>
</FrameLayout>
新的內容會陸續添加。