使用AsyncTask的加载位图图像 [英] Use AsyncTask to Load Bitmap Images
问题描述
我想有人通过我的应用程序工作负载的背景图像。我写的逻辑是这样的:
公共类ImageLoader的扩展AsyncTask的<上下文,太虚,位图> {
私人字符串URL;
私人诠释类型;
ImageLoader的(字符串的URL,整型)
{
URL =网址;
type =类型;
}
@覆盖
受保护的位图doInBackground(上下文...为arg0){
AssetManager assetMgr =为arg0 [0] .getAssets();
点阵位图= NULL;
尝试 {
位= BitmapFactory.de codeStream(assetMgr.open(URL));
}赶上(IOException异常E){
e.printStackTrace();
}
返回的位图;
}
@覆盖
保护无效onPostExecute(位图的结果){
super.onPostExecute(结果);
如果(类型== 1)
INST1 =结果;
否则,如果(类型== 2)
INST2 =结果;
否则,如果(类型== 3)
Inst3 =结果;
}
}
然而,当我尝试启动一个新的线程是这样的:
任务=新ImageLoader的(Instructions_2.png,3);
task.execute(gameContext);
但在程序中出现错误活套。prepare必须调用,其次是逻辑looper.quit()
不过,我可能会打断程序的时候我加活套。prepare(),而且没有looper.quit()来调用。
我是正确创建的任务?
编辑:
这是从什么时候我尝试运行错误日志:
任务=新ImageLoader的(gameContext,Instructions_3.png,3);
我有我把图像加载器的声明之外的开关case语句。基本上我的code是:
ImageLoader的任务;
开关(富)
{
情况下0:
...
任务=新ImageLoader的(gameContextInstructions_0.png,3);
task.execute();
打破;
情况1:
...
任务=新ImageLoader的(gameContextInstructions_1.png,3));
task.execute();
打破;
...
}
和错误日志(错误发生,每次我打了任务=新ImageLoader的(...);
行
07-20 14:23:34.276:E / AndroidRuntime(16741):致命异常:螺纹10
07-20 14:23:34.276:E / AndroidRuntime(16741):java.lang.ExceptionInInitializerError
07-20 14:23:34.276:E / AndroidRuntime(16741):在com.petronicarts.stormthecastle.MainGamePanel.update(MainGamePanel.java:2578)
07-20 14:23:34.276:E / AndroidRuntime(16741):在com.petronicarts.stormthecastle.MainThread.run(MainThread.java:63)
07-20 14:23:34.276:E / AndroidRuntime(16741):java.lang.RuntimeException的:所致。内螺纹已经不叫尺蠖prepare无法创建处理器()
。07-20 14:23:34.276:E / AndroidRuntime(16741):在android.os.Handler< INIT>(Handler.java:121)
。07-20 14:23:34.276:E / AndroidRuntime(16741):在android.os.AsyncTask $ InternalHandler< INIT>(AsyncTask.java:421)
。07-20 14:23:34.276:E / AndroidRuntime(16741):在android.os.AsyncTask $ InternalHandler< INIT>(AsyncTask.java:421)
07-20 14:23:34.276:E / AndroidRuntime(16741):在android.os.AsyncTask< clinit>(AsyncTask.java:152)
07-20 14:23:34.276:E / AndroidRuntime(16741):... 2更多
现在的问题是,你正在试图访问,并从非UI线程的UI元素进行操作。如果你改变你的的AsyncTask
如下,我相信你会好起来:
公共类ImageLoader的扩展AsyncTask的<虚空,虚空,位图> {
私人字符串URL;
私人诠释类型;
私人上下文的背景下;
私人的InputStream的;
ImageLoader的(上下文的背景下,字符串的URL,整型)
{
URL =网址;
type =类型;
ImageLoader.this.context =背景;
}
@覆盖
在preExecute保护无效()
{
AssetManager assetMgr = context.getAssets();
尝试 {
在= assetMgr.open(URL);
}赶上(IOException异常E){
e.printStackTrace();
}
}
@覆盖
受保护的位图doInBackground(虚空......为arg0){
点阵位图= NULL;
尝试 {
位= BitmapFactory.de codeStream(中);
附寄();
}赶上(IOException异常E){
e.printStackTrace();
}
返回的位图;
}
@覆盖
保护无效onPostExecute(位图的结果){
如果(类型== 1)
INST1 =结果;
否则,如果(类型== 2)
INST2 =结果;
否则,如果(类型== 3)
Inst3 =结果;
}
}
也改变你的 AyncTask
的调用是这样的:
任务=新ImageLoader的(gameContext,Instructions_2.png,3);
task.execute();
I am trying to load an image in the background as someone works through my app. The logic I wrote is this:
public class ImageLoader extends AsyncTask <Context, Void, Bitmap>{
private String URL;
private int type;
ImageLoader(String Url, int Type)
{
URL = Url;
type = Type;
}
@Override
protected Bitmap doInBackground(Context... arg0) {
AssetManager assetMgr = arg0[0].getAssets();
Bitmap bitmap = null;
try {
bitmap = BitmapFactory.decodeStream(assetMgr.open(URL));
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}
@Override
protected void onPostExecute( Bitmap result ) {
super.onPostExecute(result);
if (type == 1)
Inst1 = result;
else if (type == 2)
Inst2 = result;
else if (type == 3)
Inst3 = result;
}
}
However when I try to start a new thread like this:
task = new ImageLoader("Instructions_2.png", 3);
task.execute(gameContext);
But within the program I get the error Looper.prepare must be called, followed by the logic looper.quit()
However I seem to break the program when I add Looper.prepare(), and there is no looper.quit() to call.
Am I creating the task correctly?
EDIT:
This is the error log from when I try to run:
task = new ImageLoader(gameContext, "Instructions_3.png", 3);
I have a switch case statement that I put the image loader declaration outside of. Essentially my code is:
ImageLoader task;
switch(foo)
{
case 0:
...
task = new ImageLoader(gameContext, "Instructions_0.png", 3);
task.execute();
break;
case 1:
...
task = new ImageLoader(gameContext, "Instructions_1.png", 3));
task.execute();
break;
...
}
And the error log (error occurs every time I hit the task = new ImageLoader(...);
line
07-20 14:23:34.276: E/AndroidRuntime(16741): FATAL EXCEPTION: Thread-10
07-20 14:23:34.276: E/AndroidRuntime(16741): java.lang.ExceptionInInitializerError
07-20 14:23:34.276: E/AndroidRuntime(16741): at com.petronicarts.stormthecastle.MainGamePanel.update(MainGamePanel.java:2578)
07-20 14:23:34.276: E/AndroidRuntime(16741): at com.petronicarts.stormthecastle.MainThread.run(MainThread.java:63)
07-20 14:23:34.276: E/AndroidRuntime(16741): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
07-20 14:23:34.276: E/AndroidRuntime(16741): at android.os.Handler.<init>(Handler.java:121)
07-20 14:23:34.276: E/AndroidRuntime(16741): at android.os.AsyncTask$InternalHandler.<init>(AsyncTask.java:421)
07-20 14:23:34.276: E/AndroidRuntime(16741): at android.os.AsyncTask$InternalHandler.<init>(AsyncTask.java:421)
07-20 14:23:34.276: E/AndroidRuntime(16741): at android.os.AsyncTask.<clinit>(AsyncTask.java:152)
07-20 14:23:34.276: E/AndroidRuntime(16741): ... 2 more
The problem is that you are trying to access and operate on UI elements from a non UI thread. If you change your AsyncTask
as follows, i believe you will be ok:
public class ImageLoader extends AsyncTask <Void, Void, Bitmap>{
private String URL;
private int type;
private Context context;
private InputStream in;
ImageLoader(Context context, String Url, int Type)
{
URL = Url;
type = Type;
ImageLoader.this.context = context;
}
@Override
protected void onPreExecute()
{
AssetManager assetMgr = context.getAssets();
try {
in = assetMgr.open(URL);
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
protected Bitmap doInBackground(Void... arg0) {
Bitmap bitmap = null;
try {
bitmap = BitmapFactory.decodeStream(in);
in.close();
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}
@Override
protected void onPostExecute( Bitmap result ) {
if (type == 1)
Inst1 = result;
else if (type == 2)
Inst2 = result;
else if (type == 3)
Inst3 = result;
}
}
Also change the call of your AyncTask
to something like this:
task = new ImageLoader(gameContext, "Instructions_2.png", 3);
task.execute();
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