坐标系详解

前言

Android系统中有两种坐标系，分别为Android坐标系和View坐标系。了解这两种坐标系能够帮助我们实现View的各种操作，更好的控制View.

1.Android坐标系

在Android中，屏幕左上角的顶点作为Android坐标原点(0,0)，X轴向右是正方向，向下是Y轴正方向，如下图:

2.View坐标系

View坐标系与Android坐标系两者共同存在，他们一起存在可以更好的帮助开发者更好的控制view。如下图可以帮助我们更好的分析view坐标：

View获取自身宽高
	获取宽	获取高
方法一	width = getRight()-getLeft()	height=getBottom()-getTop()
方法二	getWidth()	getHeight()

以上两个方法获取的宽高是一致的，我们从源码的角度分别看一下 getWidth()与 getHeight()方法，如下：

/**
 * Right position of this view relative to its parent.
 *
 * @return The right edge of this view, in pixels.
 */
@ViewDebug.CapturedViewProperty
public final int getRight() {
    return mRight;
}

/** * Return the width of the your view. * 获取view的宽度 * @return The width of your view, in pixels. */@ViewDebug.ExportedProperty(category = "layout")public final int getWidth() { return mRight - mLeft;}

/**
 * Return the height of your view.
 *获取view高度
 * @return The height of your view, in pixels.
 */
@ViewDebug.ExportedProperty(category = "layout")
public final int getHeight() {
    return mBottom - mTop;
}

从上面方法我们可以看出这里是获取view的宽度，接着我们在具体看一下mRight与mLeft是什么？

/**
 * The distance in pixels from the left edge of this view's parent
 * to the left edge of this view.
 * {@hide}
 */
@ViewDebug.ExportedProperty(category = "layout")
protected int mLeft;
/**
 * The distance in pixels from the left edge of this view's parent
 * to the right edge of this view.
 * {@hide}
 */
@ViewDebug.ExportedProperty(category = "layout")
protected int mRight;

我们从注释上就可以看到 mLeft其实就是获取从父布局左侧边缘到控件(父布局里面的一个子控件)左侧边缘的一段距离。

mRight也是同样的道理，这里就不相信叙述了，自己看注释。

总结：

V iew 方法	作用
getTop()	获取View自身顶边到其父布局顶边的距离
getLeft()	获取View自身左边到其父布局左边的距离
getRight()	获取View自身右边到其父布局左边的距离
getBottom()	获取View自身底边到其父布局顶边的距离

MotionEvent提供的方法
方法	作用
getX()	获取点击事件距离控件左边的距离，即视图坐标
getY()	获取点击事件距离控件顶边的距离，即视图坐标
getRawX()	获取点击事件距离整个屏幕左边距离，即绝对坐标
getRawY()	获取点击事件距离整个屏幕顶边的的距离，即绝对坐标

eg:

getX()
/** * The visual x position of this view, in pixels. This is equivalent to the * {@link #setTranslationX(float) translationX} property plus the current * {@link #getLeft() left} property. * * @return The visual x position of this view, in pixels. / @ViewDebug.ExportedProperty(category = "drawing") public float getX() { return mLeft + getTranslationX(); } /* * The horizontal location of this view relative to its {@link #getLeft() left} position. * This position is post-layout, in addition to wherever the object's * layout placed it. * * @return The horizontal position of this view relative to its left position, in pixels. / @ViewDebug.ExportedProperty(category = "drawing") public float getTranslationX() { return mRenderNode.getTranslationX(); } /* * Returns the translation value for this display list on the X axis, in pixels. * * @see #setTranslationX(float) */ public float getTranslationX() { return nGetTranslationX(mNativeRenderNode); } private static native float nGetTranslationX(long renderNode);//底层c处理

getX()

/**
 * The visual x position of this view, in pixels. This is equivalent to the
 * {@link #setTranslationX(float) translationX} property plus the current
 * {@link #getLeft() left} property.
 *
 * @return The visual x position of this view, in pixels.
 */
@ViewDebug.ExportedProperty(category = "drawing")
public float getX() {
    return mLeft + getTranslationX();
}


/**
 * The horizontal location of this view relative to its {@link #getLeft() left} position.
 * This position is post-layout, in addition to wherever the object's
 * layout placed it.
 *
 * @return The horizontal position of this view relative to its left position, in pixels.
 */
@ViewDebug.ExportedProperty(category = "drawing")
public float getTranslationX() {
    return mRenderNode.getTranslationX();
}


/**
 * Returns the translation value for this display list on the X axis, in pixels.
 *
 * @see #setTranslationX(float)
 */
public float getTranslationX() {
    return nGetTranslationX(mNativeRenderNode);
}

private static native float nGetTranslationX(long renderNode);//底层c处理

前言

1.Android坐标系

2.View坐标系

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