一个可以一直滚动的ImageView(可做视差效果)

本文主要是介绍一个可以一直滚动的ImageView(可做视差效果)，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Java代码

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.View;
import static java.lang.Math.abs;
import static java.lang.Math.floor;
/**
* Created by thijs on 08-06-15.
*/
public class ScrollingImageView extends View {
private final int speed;
private final Bitmap bitmap;
private Rect clipBounds = new Rect();
private int offset = 0;
private boolean isStarted;
public ScrollingImageView(Context context, AttributeSet attrs) {
super(context, attrs);
TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.ParallaxView, 0, 0);
try {
speed = ta.getDimensionPixelSize(R.styleable.ParallaxView_speed, 10);
bitmap = BitmapFactory.decodeResource(getResources(), ta.getResourceId(R.styleable.ParallaxView_src, 0));
} finally {
ta.recycle();
}
start();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec), bitmap.getHeight());
}
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (canvas == null) {
return;
}
canvas.getClipBounds(clipBounds);
int normalizedOffset = offset;
int layerWidth = bitmap.getWidth();
if (offset < -layerWidth) {
offset += (int) (floor(abs(normalizedOffset) / (float) layerWidth) * layerWidth);
}
int left = offset;
while (left < clipBounds.width()) {
canvas.drawBitmap(bitmap, getBitmapLeft(layerWidth, left), 0, null);
left += layerWidth;
}
if (isStarted) {
offset -= speed;
postInvalidateOnAnimation();
}
}
private float getBitmapLeft(int layerWidth, int left) {
float bitmapLeft = left;
if (speed < 0) {
bitmapLeft = clipBounds.width() - layerWidth - left;
}
return bitmapLeft;
}
/**
* Start the animation
*/
public void start() {
if (!isStarted) {
isStarted = true;
postInvalidateOnAnimation();
}
}
/**
* Stop the animation
*/
public void stop() {
if (isStarted) {
isStarted = false;
invalidate();
}
}
}

attr.xml

Xml代码

<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="ParallaxView">
<attr name="speed" format="dimension" />
<attr name="src" format="reference" />
</declare-styleable>
</resources>

usage:

Xml代码

<com.....ScrollingImageView
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/scrolling_background"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:speed="1dp"
app:src="@drawable/scrolling_background" />

Java代码

ScrollingImageView scrollingBackground = (ScrollingImageView) loader.findViewById(R.id.scrolling_background);
scrollingBackground.stop();
scrollingBackground.start();

Parallax effect:
只要设置不同的滚动背景速率就可以达到视差效果

Java代码