How to create a beautiful wheel animation in android?

Today’s post is about animation, a beautiful animation, exploring capabilities of android.

Animation

Animation

You can click on the link to download the code.

Here we will have three java classes and no XML files.
1. GraphicsActivity.java
2. PictureLayout.java
3. Sweep.java

At first we start with PictureLayout.java

package com.example.sweep;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Picture;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;

public class PictureLayout extends ViewGroup {
    private final Picture mPicture = new Picture();

    public PictureLayout(Context context) {
        super(context);
    }

    public PictureLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public void addView(View child) {
        if (getChildCount() > 1) {
            throw new IllegalStateException("PictureLayout can host only one direct child");
        }

        super.addView(child);
    }

    @Override
    public void addView(View child, int index) {
        if (getChildCount() > 1) {
            throw new IllegalStateException("PictureLayout can host only one direct child");
        }

        super.addView(child, index);
    }

    @Override
    public void addView(View child, LayoutParams params) {
        if (getChildCount() > 1) {
            throw new IllegalStateException("PictureLayout can host only one direct child");
        }

        super.addView(child, params);
    }

    @Override
    public void addView(View child, int index, LayoutParams params) {
        if (getChildCount() > 1) {
            throw new IllegalStateException("PictureLayout can host only one direct child");
        }

        super.addView(child, index, params);
    }

    @Override
    protected LayoutParams generateDefaultLayoutParams() {
        return new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        final int count = getChildCount();

        int maxHeight = 0;
        int maxWidth = 0;

        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != GONE) {
                measureChild(child, widthMeasureSpec, heightMeasureSpec);
            }
        }

        maxWidth += getPaddingLeft() + getPaddingRight();
        maxHeight += getPaddingTop() + getPaddingBottom();

        Drawable drawable = getBackground();
        if (drawable != null) {
            maxHeight = Math.max(maxHeight, drawable.getMinimumHeight());
            maxWidth = Math.max(maxWidth, drawable.getMinimumWidth());
        }

        setMeasuredDimension(resolveSize(maxWidth, widthMeasureSpec),
                resolveSize(maxHeight, heightMeasureSpec));
    }

    private void drawPict(Canvas canvas, int x, int y, int w, int h,
                          float sx, float sy) {
        canvas.save();
        canvas.translate(x, y);
        canvas.clipRect(0, 0, w, h);
        canvas.scale(0.5f, 0.5f);
        canvas.scale(sx, sy, w, h);
        canvas.drawPicture(mPicture);
        canvas.restore();
    }

    @SuppressWarnings("unused")
	@Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(mPicture.beginRecording(getWidth(), getHeight()));
        mPicture.endRecording();

        int x = getWidth()/2;
        int y = getHeight()/2;

        if (false) {
            canvas.drawPicture(mPicture);
        } else {
            drawPict(canvas, 0, 0, x, y,  1,  1);
            drawPict(canvas, x, 0, x, y, -1,  1);
            drawPict(canvas, 0, y, x, y,  1, -1);
            drawPict(canvas, x, y, x, y, -1, -1);
        }
    }

    @Override
    public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
        location[0] = getLeft();
        location[1] = getTop();
        dirty.set(0, 0, getWidth(), getHeight());
        return getParent();
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        final int count = super.getChildCount();

        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != GONE) {
                final int childLeft = getPaddingLeft();
                final int childTop = getPaddingTop();
                child.layout(childLeft, childTop,
                        childLeft + child.getMeasuredWidth(),
                        childTop + child.getMeasuredHeight());

            }
        }
    }
}

Now our second java file, GraphicsActivity.java
No need to declare this activity in the Manifest since you are only extending it.

package com.example.sweep;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;

class GraphicsActivity extends Activity {
    // set to true to test Picture
    private static final boolean TEST_PICTURE = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public void setContentView(View view) {
        if (TEST_PICTURE) {
            ViewGroup vg = new PictureLayout(this);
            vg.addView(view);
            view = vg;
        }

        super.setContentView(view);
    }
}

Now the last java class that extends the GraphicsActivity and creates the animation.
Sweep.java

package com.example.sweep;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Shader;
import android.graphics.SweepGradient;
import android.os.Bundle;
import android.view.View;

public class Sweep extends GraphicsActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new SampleView(this));
    }

    private static class SampleView extends View {
        private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        private float mRotate;
        private Matrix mMatrix = new Matrix();
        private Shader mShader;
        private boolean mDoTiming;

        public SampleView(Context context) {
            super(context);
            setFocusable(true);
            setFocusableInTouchMode(true);

            float x = 160;
            float y = 100;
            mShader = new SweepGradient(x, y, new int[] { Color.GREEN,
                                                  Color.RED,
                                                  Color.BLUE,
                                                  Color.GREEN }, null);
            mPaint.setShader(mShader);
        }

        @Override protected void onDraw(Canvas canvas) {
            Paint paint = mPaint;
            float x = 160;
            float y = 100;

            canvas.drawColor(Color.WHITE);

            mMatrix.setRotate(mRotate, x, y);
            mShader.setLocalMatrix(mMatrix);
            mRotate += 3;
            if (mRotate >= 360) {
                mRotate = 0;
            }
            invalidate();

            if (mDoTiming) {
                long now = System.currentTimeMillis();
                for (int i = 0; i < 20; i++) {
                    canvas.drawCircle(x, y, 80, paint);
                }
                now = System.currentTimeMillis() - now;
                android.util.Log.d("skia", "sweep ms = " + (now/20.));
            }
            else {
                canvas.drawCircle(x, y, 80, paint);
            }
        }

       
    }
}

Please leave your valuable comments on this post.

You can download the source code for the above post from here.

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