先看一下RatingBar的继承关系
ProgressBar
|_ AbsSeekBar
|_ RatingBar
先来看看RatingBar的onMeasure()
@Override
protected synchronized void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
if (mSampleWidth > 0) {
// 计算宽度
final int width = mSampleWidth * mNumStars;
setMeasuredDimension(resolveSizeAndState(width, widthMeasureSpec, 0),
getMeasuredHeight());
}
}1.1 宽度计算
宽度是通过mSampleWidth乘以star数量得来，那么mSampleWidth又是怎么来的呢？
mSampleWidth定义在父类ProgressBar中：
// ProgressBar.java
// 定义
int mSampleWidth = 0;
// 构造方法
public ProgressBar(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
final TypedArray a = context.obtainStyledAttributes(
attrs, R.styleable.ProgressBar, defStyleAttr, defStyleRes);
final Drawable progressDrawable = a.getDrawable(R.styleable.ProgressBar_progressDrawable);
if (progressDrawable != null) {
// Calling setProgressDrawable can set mMaxHeight, so make sure the
// corresponding XML attribute for mMaxHeight is read after calling
// this method.
if (needsTileify(progressDrawable)) {
setProgressDrawableTiled(progressDrawable);
} else {
setProgressDrawable(progressDrawable);
}
}
}
public void setProgressDrawableTiled(Drawable d) {
if (d != null) {
d = tileify(d, false);
}
setProgressDrawable(d);
}
private Drawable tileify(Drawable drawable, boolean clip) {
...
if (drawable instanceof BitmapDrawable) {
final Drawable.ConstantState cs = drawable.getConstantState();
// 根据Drawable获取BitmapDrawable
final BitmapDrawable clone = (BitmapDrawable) cs.newDrawable(getResources());
clone.setTileModeXY(Shader.TileMode.REPEAT, Shader.TileMode.CLAMP);
if (mSampleWidth <= 0) {
// 获取bitmap的宽度
mSampleWidth = clone.getIntrinsicWidth();
}
...
}
return drawable;
}// BitmapDrawable.java
@Override
public int getIntrinsicWidth() {
return mBitmapWidth;
}
private void computeBitmapSize() {
final Bitmap bitmap = mBitmapState.mBitmap;
if (bitmap != null) {
mBitmapWidth = bitmap.getScaledWidth(mTargetDensity);
mBitmapHeight = bitmap.getScaledHeight(mTargetDensity);
} else {
mBitmapWidth = mBitmapHeight = -1;
}
}因此RatingBar的宽度只跟图片的宽度相关。
1.2 高度计算
RatingBar没有自己计算高度直接调用getMeasuredHeight() ，因此高度的计算是在父类中完成。
父类AbsSeekBar的onMeasure()实现如下：
@Override
protected synchronized void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// 注意此处并没有调用super.onMeasure();
Drawable d = getCurrentDrawable();
int thumbHeight = mThumb == null ? 0 : mThumb.getIntrinsicHeight();
int dw = 0;
int dh = 0;
if (d != null) {
dw = Math.max(mMinWidth, Math.min(mMaxWidth, d.getIntrinsicWidth()));
// getIntrinsicHeight()获取到的是drawable的原始高度
dh = Math.max(mMinHeight, Math.min(mMaxHeight, d.getIntrinsicHeight()));
dh = Math.max(thumbHeight, dh);
}
dw += mPaddingLeft + mPaddingRight;
dh += mPaddingTop + mPaddingBottom;
setMeasuredDimension(resolveSizeAndState(dw, widthMeasureSpec, 0),
resolveSizeAndState(dh, heightMeasureSpec, 0));
}因此父类AdbSeekBar是根据drawable的原始高度及minHeight，maxHeight进行计算的。
1.3 小结
RatingBar的宽度只跟图片的大小相关，高度和图片大小以及minHeight，maxHeight相关，不能根据设置的宽高自适应。那么这些图片的宽高是多少呢？
RatingBar提供了三种样式，可以从整个app的theme：Theme.MaterialComponents.Light.DarkActionBar开始寻找
<!-- 默认样式 -->
<style name="Base.Widget.AppCompat.RatingBar" parent="android:Widget.RatingBar">
<item name="android:progressDrawable">@drawable/abc_ratingbar_material</item>
<item name="android:indeterminateDrawable">@drawable/abc_ratingbar_material</item>
</style>
<!-- Indicator样式 -->
<style name="Base.Widget.AppCompat.RatingBar.Indicator" parent="android:Widget.RatingBar">
<item name="android:progressDrawable">@drawable/abc_ratingbar_indicator_material</item>
<item name="android:indeterminateDrawable">@drawable/abc_ratingbar_indicator_material</item>
<item name="android:minHeight">36dp</item>
<item name="android:maxHeight">36dp</item>
<item name="android:isIndicator">true</item>
<item name="android:thumb">@null</item>
</style>
<!-- Small样式 -->
<style name="Base.Widget.AppCompat.RatingBar.Small" parent="android:Widget.RatingBar">
<item name="android:progressDrawable">@drawable/abc_ratingbar_small_material</item>
<item name="android:indeterminateDrawable">@drawable/abc_ratingbar_small_material</item>
<item name="android:minHeight">16dp</item>
<item name="android:maxHeight">16dp</item>
<item name="android:isIndicator">true</item>
<item name="android:thumb">@null</item>
</style>其中minHeight和maxHeight可以控制控件的高度，而progressDrawable设置的图片控制着星星的大小。他们的大小分别是48dp，36dp，16dp。
注意：以上测量出来的宽高度只能控制这个view的大小，并不能改变内部星星的显示大小。
最后，说一个比较复杂的Drawable，是进度条相关的。
LayerDrawable：对应Seekbar android:progressDrawable
通常，我们用XML定义一个进度条的ProgressDrawable是这样的，
<!--ProgressDrawable-->
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@android:id/background" android:drawable="@drawable/background"/>
<item android:id="@android:id/secondaryProgress" android:drawable="@drawable/secondary_progress"/>
<item android:id="@android:id/progress" android:drawable="@drawable/progress"/>
</layer-list>而对于其中的，@drawable/progress和@drawable/secondary_progress也不是普通的drawable，
<!--@drawable/progress 定义-->
<clip xmlns:android="http://schemas.android.com/apk/res/android"
android:clipOrientation="horizontal"
android:drawable="@drawable/progress_drawable"
android:gravity="left" >
</clip>也就是说，通过XML要定义进度条的ProgressDrawable，我们需要定义多个XML文件的，还是比较复杂的。那么JavaCode实现呢？
其实，理解了XML实现的方式，下面的JavaCode就很好理解了。
LayerDrawable layerDrawable = (LayerDrawable) getProgressDrawable();
//背景
layerDrawable.setDrawableByLayerId(android.R.id.background, backgroundDrawable);
//进度条
ClipDrawable clipProgressDrawable = new ClipDrawable(progressDrawable, Gravity.LEFT, ClipDrawable.HORIZONTAL);
layerDrawable.setDrawableByLayerId(android.R.id.progress, clipProgressDrawable);
//缓冲进度条
ClipDrawable clipSecondaryProgressDrawable = new ClipDrawable(secondaryProgressDrawable, Gravity.LEFT, ClipDrawable.HORIZONTAL);
layerDrawable.setDrawableByLayerId(android.R.id.secondaryProgress, clipSecondaryProgressDrawable);二，AndRatingBar原理