[置顶] Android使用WebView加载图片防止OutOfMemoryError
分类： Android总结
2013-06-09 16:01
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Android WebView加载图片 OutOfMemoryError Android大图片
在Android中， 大图片加载或者处理很容易出来OutOfMemory，也就是内存溢出
所以在这里就使用WebView来加载大图片，但是WebView不好控制图片显示大小，也就是说
如果图片太大，webview将出一滚动条，图片过小则不可拉伸，极其影响美观。为此，作了些
修改，在一定区域内做一些图片尺寸的压缩。
主要实现方式：由WebView的父控件居中布局来控制垂直方向的居中，WebView的元素居中
来控制图片的水平居中 ，最终达到图片在屏幕的中间显示。
核心Java代码如下：
- private void showImageByWebView(String path){
- webViewLayout = (LinearLayout) findViewById(R.id.img_webview);
- webView = new WebView(this);
- String url = "file://"+ path;
- int[] wh = new int[2];
- int disenty;//屏幕密度
- WindowManager wManager = this.getWindowManager();
- DisplayMetrics disM = new DisplayMetrics();
- wManager.getDefaultDisplay().getMetrics(disM);
- disM = this.getResources().getDisplayMetrics();
- disenty = disM.disenty;
- wh[0] = dis.widthPixels;
- Rect outRect = new Rect();
- webViewLayout.getWindowVisibleDisplayFrame(outRect); //获取状态栏高度
- int contentHeight = (int) (wh[1] - this.getResources().getDimension(R.dimen.title_height) - outRect.top - 30); //获取webview应该显示的高度，屏幕高度减去标题栏高度和状态栏高度
- BitmapFactory.Options options = new BitmapFactory.Options();
- options.inJustDecodeBounds = true;
- BitmapFactory.decodeFile(path, options); // 因为设置了inJustDecodeBounds=true 所以此时返回的 bitmap 为 null,仅取出bitmap的信息,而不把它读到内存
- options.inJustDecodeBounds = false;
- int bitmapWidth = options.outWidth;
- int bitmapHeight = options.outHeight;
- String style = "";
- int[] imgDis = new int[2];
- int minHeight = getResources().getDimensionPixelSize(R.dimen.loadview_img_minheight);
- //注;由于webview将会设置settings.setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN);表示单列所以宽度适应内容大小，所以宽度大于屏幕而高度小于屏幕时不需要再压缩
- if(bitmapHeight > (float)contentHeight/disenty){
- double scale = 0.00f;
- scale = (double)contentHeight / bitmapHeight;
- imgDis[0] = (int) (scale * bitmapWidth / (disenty + 0.1));//这里加上了0.1的原因与以上减30一样，webview宽高肯定大于图片内容所显示的宽度，里面还会有padding属性
- imgDis[1] = (int) (scale * bitmapHeight / (disenty + 0.1));
- style = "style=\"width: " + imgDis[0] + "px; height: " + imgDis[1] + "px;\"";
- }else if(bitmapHeight < minHeight){
- double scale = (double)minHeight/bitmapHeight ;
- int width = (int) (scale * bitmapWidth);
- style = "style=\"width: " + width / disenty + "px; height: " + minHeight / disenty + "px;\"";
- }
- StringBuffer data = new StringBuffer();
- data.append("<html><center><img src=\"")
- .append(url)
- .append("\" ")
- .append(style)
- .append("></center></html>");
- webView.loadDataWithBaseURL(url, data.toString(), "text/html","UTF-8","");
- webView.setScrollContainer(false);
- webView.setScrollbarFadingEnabled(false);
- WebSettings settings = webView.getSettings();
- settings.setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN);
- settings.setBuiltInZoomControls(false); // 设置显示缩放按钮
- settings.setSupportZoom(true); //支持缩放
- //webView.setInitialScale(100);
- // settings.setUseWideViewPort(true); //双击放大，但是在这里如果放大将会有问题
- // settings.setLoadWithOverviewMode(true);//多窗口预览方式显示
- webView.setBackgroundColor(0x00000000);
- // View zoomControls = webView.getZoomControls();
- // LayoutParams paramszoom = new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
- // zoomControls.setLayoutParams(paramszoom);
- LayoutParams params = new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT, Gravity.CENTER);
- params.width = LayoutParams.WRAP_CONTENT;
- params.height = LayoutParams.WRAP_CONTENT;
- webView.setMinimumHeight(500);
- webViewLayout.addView(webView, params);
- }
private void showImageByWebView(String path){
webViewLayout = (LinearLayout) findViewById(R.id.img_webview);
webView = new WebView(this);
String url = "file://"+ path;
int[] wh = new int[2];
int disenty;//屏幕密度
WindowManager wManager = this.getWindowManager();
DisplayMetrics disM = new DisplayMetrics();
wManager.getDefaultDisplay().getMetrics(disM);
disM = this.getResources().getDisplayMetrics();
disenty = disM.disenty;
wh[0] = dis.widthPixels;
Rect outRect = new Rect();
webViewLayout.getWindowVisibleDisplayFrame(outRect); //获取状态栏高度
int contentHeight = (int) (wh[1] - this.getResources().getDimension(R.dimen.title_height) - outRect.top - 30); //获取webview应该显示的高度，屏幕高度减去标题栏高度和状态栏高度
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(path, options); // 因为设置了inJustDecodeBounds=true 所以此时返回的 bitmap 为 null,仅取出bitmap的信息,而不把它读到内存
options.inJustDecodeBounds = false;
int bitmapWidth = options.outWidth;
int bitmapHeight = options.outHeight;
String style = "";
int[] imgDis = new int[2];
int minHeight = getResources().getDimensionPixelSize(R.dimen.loadview_img_minheight);
//注;由于webview将会设置settings.setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN);表示单列所以宽度适应内容大小，所以宽度大于屏幕而高度小于屏幕时不需要再压缩
if(bitmapHeight > (float)contentHeight/disenty){
double scale = 0.00f;
scale = (double)contentHeight / bitmapHeight;
imgDis[0] = (int) (scale * bitmapWidth / (disenty + 0.1));//这里加上了0.1的原因与以上减30一样，webview宽高肯定大于图片内容所显示的宽度，里面还会有padding属性
imgDis[1] = (int) (scale * bitmapHeight / (disenty + 0.1));
style = "style=\"width: " + imgDis[0] + "px; height: " + imgDis[1] + "px;\"";
}else if(bitmapHeight < minHeight){
double scale = (double)minHeight/bitmapHeight ;
int width = (int) (scale * bitmapWidth);
style = "style=\"width: " + width / disenty + "px; height: " + minHeight / disenty + "px;\"";
}
StringBuffer data = new StringBuffer();
data.append("<html><center><img src=\"")
.append(url)
.append("\" ")
.append(style)
.append("></center></html>");
webView.loadDataWithBaseURL(url, data.toString(), "text/html","UTF-8","");
webView.setScrollContainer(false);
webView.setScrollbarFadingEnabled(false);
WebSettings settings = webView.getSettings();
settings.setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN);
settings.setBuiltInZoomControls(false); // 设置显示缩放按钮
settings.setSupportZoom(true); //支持缩放
//webView.setInitialScale(100);
// settings.setUseWideViewPort(true); //双击放大，但是在这里如果放大将会有问题
// settings.setLoadWithOverviewMode(true);//多窗口预览方式显示
webView.setBackgroundColor(0x00000000);
// View zoomControls = webView.getZoomControls();
// LayoutParams paramszoom = new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
// zoomControls.setLayoutParams(paramszoom);
LayoutParams params = new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT, Gravity.CENTER);
params.width = LayoutParams.WRAP_CONTENT;
params.height = LayoutParams.WRAP_CONTENT;
webView.setMinimumHeight(500);
webViewLayout.addView(webView, params);
}
核心布局代码如下：
- <?xml version="1.0" encoding="utf-8"?>
- <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent"
- android:orientation="vertical" >
- <!-- .....-->
- <LinearLayout
- android:id="@+id/img_webview"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent"
- android:layout_centerInParent="true"
- android:minHeight="200dip"
- android:minWidth="200dip"
- android:gravity="center"
- android:paddingTop="@dimen/title_normal_height"
- />
- </RelativeLayout>
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<!-- .....-->
<LinearLayout
android:id="@+id/img_webview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_centerInParent="true"
android:minHeight="200dip"
android:minWidth="200dip"
android:gravity="center"
android:paddingTop="@dimen/title_normal_height"
/>
</RelativeLayout>