旋转时绘制多个位图

Question

I have an activity that rotates png image by the SeekBar progress. And it draws me multiple needles. why it does that? The needle and the speedometer are not perfect, they are just for testings :)

In onCreate:

@Override
public void onCreate(Bundle savedInstanceState) {

...

    iv = (ImageView)findViewById(R.id.imageView1);
    bMap = BitmapFactory.decodeResource(getResources(), R.drawable.rodykle);
    workingBitmap = Bitmap.createBitmap(bMap);
    mutableBitmap = workingBitmap.copy(Bitmap.Config.ARGB_8888, true);
    yourCanvas = new Canvas(mutableBitmap);

later i use this void

  public void drawneedle(){
    yourCanvas.rotate(speed, mutableBitmap.getWidth()/2, mutableBitmap.getHeight()/2);
    yourCanvas.save(Canvas.MATRIX_SAVE_FLAG);
    yourCanvas.drawBitmap(mutableBitmap, 0,0, null);
    yourCanvas.restore();
    iv.setImageBitmap(mutableBitmap);
}

Layout

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:mtr="http://schemas.android.com/apk/res/com.mindtherobot.samples.thermometer"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="top"
    android:orientation="vertical" >

    <SeekBar
        android:id="@+id/seekBar1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:paddingLeft="30dp"
        android:paddingRight="30dp"
        android:max="270" />

    <RelativeLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:background="@drawable/spidometras" >

        <ImageView
            android:id="@+id/imageView1"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"/>

        <TextView
            android:id="@+id/textView1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="40sp"
            android:layout_alignParentBottom="true"
            android:layout_alignParentLeft="true" />

    </RelativeLayout>


</LinearLayout>

Answer 1

Do you clear the inner circle of the previously drawn content?

You can do that with canvas.drawColor(0, Mode.CLEAR);

Also, in my opinion, you need to add the configChanges flag to your activity's tag in the AndroidManifest.xml file, to prevent onCreate to run more than once when activity rotates.

android:configChanges="orientation|screenLayout|screenSize|smallestScreenSize"

To know that the activity rotated, you need to override the

onConfigurationChanged(Config newConfig) 

method and check the new orientation of the newConfig variable