我正在尝试扩展ImageView并添加阴影。但是我遇到了一个问题，阴影被视图边界裁剪，看起来很糟糕：
LayoutParams编程方式设置宽度/高度，以及尝试使用不同的XML属性，如android:adjustViewBounds，但显示没有改变。同样，设置android:layout_margin无效，无法防止阴影被剪切。
有人能帮我找出如何避免这种剪切吗？我确定我在这里忽略了一些明显的东西。
更新：
此时我的代码非常特定，只适用于一个情况：我正在尝试在圆形位图下绘制一个圆形“阴影”。很明显，视图边界导致了剪切，但我还没有找到解决方案，可以让我扩展视图边界。
在xxhdpi屏幕上，密度为3.0时，56dp图像的宽度和高度分别为168px。在添加2dp的宽度和高度以便偏移后，layoutParams的宽度为174，高度为174。
我的基本方法是让超级ImageView做它该做的事情，并在xml中指定绘制位图，而我只想额外绘制一些东西。这种方法从根本上有缺陷吗？在onLayout中，我使用宽度或高度中较大的那个来确定阴影圆的半径：radius = Max(width, height) / 2。我以此半径画一个圆，并将其圆心放置在(Cx, Cy)处，其中Cx是宽度的中点加上一个x偏移量，Cy是高度的中点加上一个y偏移量，以创建阴影效果。我使用画布将附加圆绘制到位图中，并在onDraw中将我的圆放置在画布上，然后允许ImageView超级onDraw处理源位图。
此外，在我的onLayout中，我尝试考虑x和y偏移距离，并通过LayoutParams将它们添加到我的视图的宽度和高度中，但当视图被绘制时，视图的大小没有变化。
这是我正在使用的代码: https://gitlab.com/dm78/ImageViewWithShadowExample/
以下是相关代码:
activity_main.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<dm78.example.imageviewwithshadowexample.CustomShadowImageView
android:id="@+id/circle"
android:layout_gravity="center"
android:src="@drawable/circle"
android:layout_margin="16dp"
android:layout_width="56dp"
android:layout_height="56dp"/>
</FrameLayout>
CustomShadowImageView.java
package dm78.example.imageviewwithshadowexample;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Build;
import android.renderscript.Allocation;
import android.renderscript.Element;
import android.renderscript.RenderScript;
import android.renderscript.ScriptIntrinsicBlur;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.util.TypedValue;
import android.widget.FrameLayout;
import android.widget.ImageView;
public class CustomShadowImageView extends ImageView {
public static final String TAG = CustomShadowImageView.class.getSimpleName();
public static final float SHADOW_RADIUS_DP = 3f;
public static final float SHADOW_X_OFFSET_DP = 2f;
public static final float SHADOW_Y_OFFSET_DP = 2f;
private Paint mPaint;
private float mShadowRadius;
private float radius;
private float cx;
private float cy;
private float mShadowXOffset;
private float mShadowYOffset;
private Bitmap mShadowBitmap;
private FrameLayout.LayoutParams layoutParams;
private boolean expanded;
public CustomShadowImageView(Context context) {
super(context);
init();
}
public CustomShadowImageView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public CustomShadowImageView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
Log.d(TAG, "init " + this.hashCode());
DisplayMetrics dm = getContext().getResources().getDisplayMetrics();
mShadowRadius = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, SHADOW_RADIUS_DP, dm);
mShadowXOffset = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, SHADOW_X_OFFSET_DP, dm);
mShadowYOffset = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, SHADOW_Y_OFFSET_DP, dm);
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
//noinspection deprecation
int shadowColor = getContext().getResources().getColor(R.color.shadow);
mPaint.setColor(shadowColor);
expanded = false;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
Log.d(TAG, String.format("onMeasure %d w: %d, h: %d", this.hashCode(), MeasureSpec.getSize(widthMeasureSpec), MeasureSpec.getSize(heightMeasureSpec)));
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
Log.d(TAG, String.format("onLayout %d changed: %b, l: %d, t: %d, r: %d, b: %d", this.hashCode(), changed, left, top, right, bottom));
super.onLayout(changed, left, top, right, bottom);
if (changed) {
if (!expanded) {
layoutParams = (FrameLayout.LayoutParams) getLayoutParams();
layoutParams.width = (int) (layoutParams.width + mShadowXOffset);
layoutParams.height = (int) (layoutParams.height + mShadowYOffset);
expanded = true;
}
cx = (right - left) / 2 + mShadowXOffset;
cy = (bottom - top) / 2 + mShadowYOffset;
boolean widthGreater = (right - left) > (bottom - top);
radius = (widthGreater ? right - left : bottom - top) / 2;
if (mShadowBitmap == null) {
Bitmap bitmap = Bitmap.createBitmap(right - left, bottom - top, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
canvas.drawCircle(cx, cy, radius, mPaint);
if (Build.VERSION.SDK_INT >= 17 && !isInEditMode()) {
RenderScript rs = RenderScript.create(getContext());
Allocation input = Allocation.createFromBitmap(rs, bitmap, Allocation.MipmapControl.MIPMAP_NONE, Allocation.USAGE_SCRIPT);
Allocation output = Allocation.createTyped(rs, input.getType());
ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
script.setRadius(mShadowRadius);
script.setInput(input);
script.forEach(output);
output.copyTo(bitmap);
}
mShadowBitmap = bitmap;
}
}
}
@Override
protected void onDraw(Canvas canvas) {
Log.d(TAG, "onDraw " + this.hashCode());
canvas.drawBitmap(mShadowBitmap, mShadowXOffset, mShadowYOffset, null);
super.onDraw(canvas);
}
}
android:clipChildren="false"呢？ - ci_canvas.clipRect寄予厚望，但它也无效。 - dm78