我想在画布上绘制圆圈。目前我可以在按钮点击时执行此操作,但是在加载Fragment
时我也需要执行相同的操作。以下是我的Fragment
代码。
public class StepTwentyOneFragment extends Fragment {
private CanvasView customCanvas;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.step21_fragment, container, false);
customCanvas=(CanvasView)v.findViewById(R.id.signature_canvas);
final Button button1=(Button)v.findViewById(R.id.step18button1);
float radius=(customCanvas.getCanvasWidth()/2) - ((customCanvas.getCanvasWidth()/2)/100)*60;
new MyAsyncTask(customCanvas).execute();
button1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(v.getId()==R.id.step18button1){
float radius=(customCanvas.getCanvasWidth()/2) - ((customCanvas.getCanvasWidth()/2)/100)*60;
customCanvas.drawCircle(radius);
Log.d("An_Width", "" + customCanvas.getCanvasWidth());
Log.d("An_Height" ,""+ customCanvas.getCanvasHeight());
v.setBackgroundResource(R.drawable.button_border_5);
button1.setTextColor(Color.WHITE);
}
}
});
return v;
}
public static StepTwentyOneFragment newInstance() {
StepTwentyOneFragment f = new StepTwentyOneFragment();
Bundle b = new Bundle();
f.setArguments(b);
return f;
}
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if(isVisibleToUser) {
Activity a = getActivity();
if(a != null) a.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
}
}
public class MyAsyncTask extends AsyncTask<Void, Void, Void> {
CanvasView myTaskView;
MyAsyncTask(CanvasView v){
myTaskView = v;
}
@Override
protected Void doInBackground(Void... arg0) {
myTaskView.drawCircle(150);
return null;
}
}
}
以下是我的Canvas
代码
public class CanvasView extends View {
public int width;
public int height;
private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
Context context;
private Paint mPaint;
private float mX, mY;
private static final float TOLERANCE = 5;
private int canvasHeight, canvasWidth;
private float radius;
public CanvasView(Context c, AttributeSet attrs) {
super(c, attrs);
context = c;
mPath = new Path();
mPaint = new Paint();
mPaint.setStrokeWidth(3);
mPaint.setColor(Color.CYAN);
}
// override onDraw
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
mCanvas=canvas;
Drawable d = getResources().getDrawable(R.drawable.circle_1);
canvasHeight= canvas.getHeight();
canvasWidth= canvas.getWidth();
Log.d("Height - "," / "+canvas.getHeight());
Log.d("Width - "," / "+canvas.getWidth());
// DisplayMetrics displaymetrics = new DisplayMetrics();
// ((Activity)context).getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
// int height = displaymetrics.heightPixels;
// int width = displaymetrics.widthPixels;
float h=canvasHeight/2;
float w=canvasWidth/2;
d.setBounds(0, 0, canvasWidth, canvasHeight);
d.draw(canvas);
canvas.drawCircle(w, h, radius, mPaint);
}
public void clear2(){
radius=0;
//important. Refreshes the view by calling onDraw function
invalidate();
}
public void drawCircle(float radius1) {
radius=radius1;
//important. Refreshes the view by calling onDraw function
invalidate();
}
public int getCanvasHeight()
{
return canvasHeight;
}
public int getCanvasWidth()
{
return canvasWidth;
}
}
然而,在Fragment
内MyAsyncTask
内,它显示代码行Method drawCircle must be called from the UI thread, currently inferred thread is worker
的错误myTaskView.drawCircle(150);
我该如何解决这个问题?
答案 0 :(得分:1)
如果要在doInBackground()中实现,则无法在UI线程上显示任何内容。它是为了后台任务。要更新UI,必须在postexecute()中实现方法。
详细了解AsyncTask:https://developer.android.com/reference/android/os/AsyncTask.html
清除您的概念,然后使用AsynTask会更容易。
AsyncTask的基本结构:
private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
protected Long doInBackground(URL... urls) {
int count = urls.length;
long totalSize = 0;
for (int i = 0; i < count; i++) {
totalSize += Downloader.downloadFile(urls[i]);
publishProgress((int) ((i / (float) count) * 100));
// Escape early if cancel() is called
if (isCancelled()) break;
}
return totalSize;
}
protected void onProgressUpdate(Integer... progress) {
setProgressPercent(progress[0]);
}
protected void onPostExecute(Long result) {
showDialog("Downloaded " + result + " bytes");
}
}