Android Drawable Resource学习（十二）、ShapeDrawable还是GradientDrawable？
一、发现奇怪的问题？
在研究Android Drawable资源的时候，发现了一个奇怪的问题。在官方API介绍中：
ShapeDrawable 介绍：This object can be defined in an XML file with the <shape> element（这个对象可以用<shape>元素在xml文件中定义）
GradientDrawable 介绍：This object can be defined in an XML file with the <shape> element（这个对象可以用<shape>元素在xml文件中定义）
两者的介绍一模一样，都说可以使用<shape>标签在xml文件中定义。
那么，到底用<shape>标签定义的是什么的呢？经过下面的实验：
在shape.xml中定义：
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
<gradient
android:startColor="#FFFF0000"
android:endColor="#80FF00FF"
android:angle="45"/>
<padding android:left="7dp"
android:top="7dp"
android:right="7dp"
android:bottom="7dp" />
<corners android:radius="8dp" />
</shape>
在layout文件中使用：
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@drawable/gradient_box"
android:text="测试" />
在java代码中控制：
TextView textView=(TextView)findViewById(R.id.textView);
ShapeDrawable gradientDrawable=(ShapeDrawable)textView.getBackground();结果发现，报错了：
:java.lang.ClassCastException: android.graphics.drawable.GradientDrawable不能将GradientDrawable转换为ShapeDrawable。
可见，使用<shape>标签定义的是GradientDrawable。
并且，在官方API Drawable Resource中ShapeDrawable介绍到：
compiled resource datatype:
Resource pointer to a GradientDrawable.编译资源类型
指向GradientDrawable的指针。
可见，编译的类型是GradientDrawable。
那么，ShapeDrawable是怎么定义的，找了网上的资料，结果硬是没找到如何在XML文件中定义它，只能通过代码的方式实现。如何使用它在后面再介绍。
二、使用GradientDrawable
GradientDrawable的作用在于定于各种样式的渐变。在XML文件中使用<shape>元素定义。- 文件位置：
-
res/drawable/filename.xml
文件名即资源ID - 编译资源类型：
-
指向
GradientDrawable. - 资源引用
-
In Java:
R.drawable.filename
In XML:@[package:]drawable/filename - 语法
-
<?xml version="1.0" encoding="utf-8"?> <shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape=["rectangle" | "oval" | "line" | "ring"] > <corners android:radius="integer" android:topLeftRadius="integer" android:topRightRadius="integer" android:bottomLeftRadius="integer" android:bottomRightRadius="integer" /> <gradient android:angle="integer" android:centerX="integer" android:centerY="integer" android:centerColor="integer" android:endColor="color" android:gradientRadius="integer" android:startColor="color" android:type=["linear" | "radial" | "sweep"] android:useLevel=["true" | "false"] /> <padding android:left="integer" android:top="integer" android:right="integer" android:bottom="integer" /> <size android:width="integer" android:height="integer" /> <solid android:color="color" /> <stroke android:width="integer" android:color="color" android:dashWidth="integer" android:dashGap="integer" /> </shape>
- 元素：
-
<padding> -
内容与视图边界的距离 - 示例：
-
XML file saved at
res/drawable/gradient_box.xml:<?xml version="1.0" encoding="utf-8"?> <shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle"> <gradient android:startColor="#FFFF0000" android:endColor="#80FF00FF" android:angle="45"/> <padding android:left="7dp" android:top="7dp" android:right="7dp" android:bottom="7dp" /> <corners android:radius="8dp" /> </shape>
This layout XML applies the shape drawable to a View:
<TextView android:background="@drawable/gradient_box" android:layout_height="wrap_content" android:layout_width="wrap_content" />
This application code gets the shape drawable and applies it to a View:
Resources res =
getResources(); Drawable shape = res.getDrawable(R.drawable.gradient_box); TextView tv = (TextView)findViewByID(R.id.textview); tv.setBackground(shape); - 参考：
-
ShapeDrawable
下面是API的Demo：
package com.example.shapedrawable;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Picture;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.GradientDrawable;
import android.graphics.drawable.ShapeDrawable;
import android.os.Bundle;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.widget.TextView;
public class MainActivity extends GraphicsActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new SampleView(this));
}
private static class SampleView extends View {
private Path mPath;
private Paint mPaint;
private Rect mRect;
private GradientDrawable mDrawable;
public SampleView(Context context) {
super(context);
setFocusable(true);
mPath = new Path();
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mRect = new Rect(0, 0, 120, 120);
mDrawable = new GradientDrawable(
GradientDrawable.Orientation.TL_BR, new int[] { 0xFFFF0000,
0xFF00FF00, 0xFF0000FF });
mDrawable.setShape(GradientDrawable.RECTANGLE);
mDrawable.setGradientRadius((float) (Math.sqrt(2) * 60));
}
static void setCornerRadii(GradientDrawable drawable, float r0,
float r1, float r2, float r3) {
drawable.setCornerRadii(new float[] { r0, r0, r1, r1, r2, r2, r3,
r3 });
}
//重点的绘制过程
@Override
protected void onDraw(Canvas canvas) {
mDrawable.setBounds(mRect);
float r = 16;
canvas.save();
canvas.translate(10, 10);
mDrawable.setGradientType(GradientDrawable.LINEAR_GRADIENT);
setCornerRadii(mDrawable, r, r, 0, 0);
mDrawable.draw(canvas);
canvas.restore();
canvas.save();
canvas.translate(10 + mRect.width() + 10, 10);
mDrawable.setGradientType(GradientDrawable.RADIAL_GRADIENT);
setCornerRadii(mDrawable, 0, 0, r, r);
mDrawable.draw(canvas);
canvas.restore();
canvas.translate(0, mRect.height() + 10);
canvas.save();
canvas.translate(10, 10);
mDrawable.setGradientType(GradientDrawable.SWEEP_GRADIENT);
setCornerRadii(mDrawable, 0, r, r, 0);
mDrawable.draw(canvas);
canvas.restore();
canvas.save();
canvas.translate(10 + mRect.width() + 10, 10);
mDrawable.setGradientType(GradientDrawable.LINEAR_GRADIENT);
setCornerRadii(mDrawable, r, 0, 0, r);
mDrawable.draw(canvas);
canvas.restore();
canvas.translate(0, mRect.height() + 10);
canvas.save();
canvas.translate(10, 10);
mDrawable.setGradientType(GradientDrawable.RADIAL_GRADIENT);
setCornerRadii(mDrawable, r, 0, r, 0);
mDrawable.draw(canvas);
canvas.restore();
canvas.save();
canvas.translate(10 + mRect.width() + 10, 10);
mDrawable.setGradientType(GradientDrawable.SWEEP_GRADIENT);
setCornerRadii(mDrawable, 0, r, 0, r);
mDrawable.draw(canvas);
canvas.restore();
}
}
}
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);
}
}
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();
}
@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());
}
}
}
}
三、ShapeDrawable的使用
ShapeDrawable没有发现如何在XML文件中定义使用，所以应该不属于Drawable Resource。这个留到后面学习Graphics在看。