我有一个ImageView正在显示png的png，该png的纵横比比设备的纵横比大（垂直地说-表示它更长）。我想在保持宽高比，匹配父级的宽度以及将imageview固定到屏幕顶部的同时显示此内容。
我使用CENTER_CROP缩放比例类型时遇到的问题是，它将（可以理解）将缩放后的图像居中，而不是将图像视图的顶部边缘与顶部边缘对齐。
问题FIT_START在于图像将适合屏幕高度，而不适合宽度。
我已经解决了这个问题，方法是使用自定义ImageView并onDraw(Canvas)使用画布手动覆盖和处理此问题；这种方法的问题是：1）我担心可能有一个更简单的解决方案，2）super(AttributeSet)当堆具有3 mb可用空间时，尝试在构造函数中设置330kb的src img 时，在构造函数中调用时收到VM mem异常（堆大小为6 mb），无法找出原因。
任何想法/建议/解决方案都非常受欢迎:)
谢谢
ps：我认为一个解决方案可能是使用矩阵比例类型，然后自己做，但这似乎比我当前的解决方案相同或更多！
Answers:
好的，我有一个可行的解决方案。来自Darko的提示使我再次查看了ImageView类（谢谢），并已使用Matrix应用了转换（如我最初所怀疑的，但第一次尝试却没有成功！）。在我的自定义imageView类中，我在构造函数中调用setScaleType(ScaleType.MATRIX)after super()，并具有以下方法。
@Override
protected boolean setFrame(int l, int t, int r, int b)
{
Matrix matrix = getImageMatrix();
float scaleFactor = getWidth()/(float)getDrawable().getIntrinsicWidth();
matrix.setScale(scaleFactor, scaleFactor, 0, 0);
setImageMatrix(matrix);
return super.setFrame(l, t, r, b);
}我将int放置setFrame()在ImageView 中的方法中，对它的调用configureBounds()位于该方法内，这是所有缩放和矩阵填充发生的地方，因此对我来说似乎很合理（例如，如果您不同意）
以下是AOSP的super.setFrame（）方法
@Override
protected boolean setFrame(int l, int t, int r, int b) {
boolean changed = super.setFrame(l, t, r, b);
mHaveFrame = true;
configureBounds();
return changed;
}在这里找到完整的类src
这是我在底部居中的代码。顺便说一句。Dori的代码中的一个小错误：由于在super.frame()最后调用，该getWidth()方法可能返回错误的值。如果您想将其居中放置在顶部，只需删除postTranslate行即可。令人高兴的是，使用此代码，您可以将其移动到所需的任何位置。（对，居中=>没问题；）
public class CenterBottomImageView extends ImageView {
public CenterBottomImageView(Context context) {
super(context);
setup();
}
public CenterBottomImageView(Context context, AttributeSet attrs) {
super(context, attrs);
setup();
}
public CenterBottomImageView(Context context, AttributeSet attrs,
int defStyle) {
super(context, attrs, defStyle);
setup();
}
private void setup() {
setScaleType(ScaleType.MATRIX);
}
@Override
protected boolean setFrame(int frameLeft, int frameTop, int frameRight, int frameBottom) {
if (getDrawable() == null) {
return super.setFrame(frameLeft, frameTop, frameRight, frameBottom);
}
float frameWidth = frameRight - frameLeft;
float frameHeight = frameBottom - frameTop;
float originalImageWidth = (float)getDrawable().getIntrinsicWidth();
float originalImageHeight = (float)getDrawable().getIntrinsicHeight();
float usedScaleFactor = 1;
if((frameWidth > originalImageWidth) || (frameHeight > originalImageHeight)) {
// If frame is bigger than image
// => Crop it, keep aspect ratio and position it at the bottom and center horizontally
float fitHorizontallyScaleFactor = frameWidth/originalImageWidth;
float fitVerticallyScaleFactor = frameHeight/originalImageHeight;
usedScaleFactor = Math.max(fitHorizontallyScaleFactor, fitVerticallyScaleFactor);
}
float newImageWidth = originalImageWidth * usedScaleFactor;
float newImageHeight = originalImageHeight * usedScaleFactor;
Matrix matrix = getImageMatrix();
matrix.setScale(usedScaleFactor, usedScaleFactor, 0, 0); // Replaces the old matrix completly
//comment matrix.postTranslate if you want crop from TOP
matrix.postTranslate((frameWidth - newImageWidth) /2, frameHeight - newImageHeight);
setImageMatrix(matrix);
return super.setFrame(frameLeft, frameTop, frameRight, frameBottom);
}
}(r-l)吗？
if((frameWidth > originalImageWidth) || (frameHeight > originalImageHeight))应该将线颠倒吗？换句话说，您是否应该测试图像是否大于框架？我建议用if((originalImageWidth > frameWidth ) || (originalImageHeight > frameHeight ))
((View) getParent()).getWidth()，因为ImageView有MATCH_PARENT
您无需编写自定义图像视图即可获得该TOP_CROP功能。您只需要修改matrix的ImageView。
设置scaleType到matrix为ImageView：
<ImageView
android:id="@+id/imageView"
android:contentDescription="Image"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:src="@drawable/image"
android:scaleType="matrix"/>为设置自定义矩阵ImageView：
final ImageView imageView = (ImageView) findViewById(R.id.imageView);
final Matrix matrix = imageView.getImageMatrix();
final float imageWidth = imageView.getDrawable().getIntrinsicWidth();
final int screenWidth = getResources().getDisplayMetrics().widthPixels;
final float scaleRatio = screenWidth / imageWidth;
matrix.postScale(scaleRatio, scaleRatio);
imageView.setImageMatrix(matrix);这样做将为您提供TOP_CROP功能。
scaleType改为，centerCrop否则我将在边缘看到空白。
此示例适用于在创建对象+进行一些优化后加载的图像。我在代码中添加了一些注释，以解释发生了什么。
切记致电：
imageView.setScaleType(ImageView.ScaleType.MATRIX);要么
android:scaleType="matrix"Java来源：
import com.appunite.imageview.OverlayImageView;
public class TopAlignedImageView extends ImageView {
private Matrix mMatrix;
private boolean mHasFrame;
@SuppressWarnings("UnusedDeclaration")
public TopAlignedImageView(Context context) {
this(context, null, 0);
}
@SuppressWarnings("UnusedDeclaration")
public TopAlignedImageView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
@SuppressWarnings("UnusedDeclaration")
public TopAlignedImageView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mHasFrame = false;
mMatrix = new Matrix();
// we have to use own matrix because:
// ImageView.setImageMatrix(Matrix matrix) will not call
// configureBounds(); invalidate(); because we will operate on ImageView object
}
@Override
protected boolean setFrame(int l, int t, int r, int b)
{
boolean changed = super.setFrame(l, t, r, b);
if (changed) {
mHasFrame = true;
// we do not want to call this method if nothing changed
setupScaleMatrix(r-l, b-t);
}
return changed;
}
private void setupScaleMatrix(int width, int height) {
if (!mHasFrame) {
// we have to ensure that we already have frame
// called and have width and height
return;
}
final Drawable drawable = getDrawable();
if (drawable == null) {
// we have to check if drawable is null because
// when not initialized at startup drawable we can
// rise NullPointerException
return;
}
Matrix matrix = mMatrix;
final int intrinsicWidth = drawable.getIntrinsicWidth();
final int intrinsicHeight = drawable.getIntrinsicHeight();
float factorWidth = width/(float) intrinsicWidth;
float factorHeight = height/(float) intrinsicHeight;
float factor = Math.max(factorHeight, factorWidth);
// there magic happen and can be adjusted to current
// needs
matrix.setTranslate(-intrinsicWidth/2.0f, 0);
matrix.postScale(factor, factor, 0, 0);
matrix.postTranslate(width/2.0f, 0);
setImageMatrix(matrix);
}
@Override
public void setImageDrawable(Drawable drawable) {
super.setImageDrawable(drawable);
// We have to recalculate image after chaning image
setupScaleMatrix(getWidth(), getHeight());
}
@Override
public void setImageResource(int resId) {
super.setImageResource(resId);
// We have to recalculate image after chaning image
setupScaleMatrix(getWidth(), getHeight());
}
@Override
public void setImageURI(Uri uri) {
super.setImageURI(uri);
// We have to recalculate image after chaning image
setupScaleMatrix(getWidth(), getHeight());
}
// We do not have to overide setImageBitmap because it calls
// setImageDrawable method
}基于Dori，我正在使用一种解决方案，该解决方案可以根据图像的宽度或高度缩放图像以始终填充周围的容器。这允许缩放图像以使用图像的左上角而不是中心作为原点来填充整个可用空间（CENTER_CROP）：
@Override
protected boolean setFrame(int l, int t, int r, int b)
{
Matrix matrix = getImageMatrix();
float scaleFactor, scaleFactorWidth, scaleFactorHeight;
scaleFactorWidth = (float)width/(float)getDrawable().getIntrinsicWidth();
scaleFactorHeight = (float)height/(float)getDrawable().getIntrinsicHeight();
if(scaleFactorHeight > scaleFactorWidth) {
scaleFactor = scaleFactorHeight;
} else {
scaleFactor = scaleFactorWidth;
}
matrix.setScale(scaleFactor, scaleFactor, 0, 0);
setImageMatrix(matrix);
return super.setFrame(l, t, r, b);
}我希望这会有所帮助-在我的项目中像对待东西一样工作。
这些解决方案都不适合我，因为我想要一个支持水平或垂直方向上任意裁切的类，并且希望它允许我动态更改裁切。我还需要Picasso兼容性，而Picasso会懒惰地设置图像可绘制对象。
我的实现直接从AOSP中的ImageView.java改编而来。要使用它，请在XML中这样声明：
<com.yourapp.PercentageCropImageView
android:id="@+id/view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="matrix"/>从源头上，如果您希望获得丰收，请致电：
imageView.setCropYCenterOffsetPct(0f);如果您希望收成不好，请致电：
imageView.setCropYCenterOffsetPct(1.0f);如果您希望在收割时下降1/3，请致电：
imageView.setCropYCenterOffsetPct(0.33f);此外，如果您选择使用其他裁剪方法，例如fit_center，则可以这样做，并且不会触发任何此自定义逻辑。（其他实现仅允许您使用其裁剪方法）。
最后，我添加了一个方法redraw（），因此，如果您选择在代码中动态更改您的裁剪方法/ scaleType，则可以强制视图重新绘制。例如：
fullsizeImageView.setScaleType(ScaleType.FIT_CENTER);
fullsizeImageView.redraw();要返回到自定义的中上三等作物，请致电：
fullsizeImageView.setScaleType(ScaleType.MATRIX);
fullsizeImageView.redraw();这是课程：
/*
* Adapted from ImageView code at:
* http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.4.4_r1/android/widget/ImageView.java
*/
import android.content.Context;
import android.graphics.Matrix;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.widget.ImageView;
public class PercentageCropImageView extends ImageView{
private Float mCropYCenterOffsetPct;
private Float mCropXCenterOffsetPct;
public PercentageCropImageView(Context context) {
super(context);
}
public PercentageCropImageView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public PercentageCropImageView(Context context, AttributeSet attrs,
int defStyle) {
super(context, attrs, defStyle);
}
public float getCropYCenterOffsetPct() {
return mCropYCenterOffsetPct;
}
public void setCropYCenterOffsetPct(float cropYCenterOffsetPct) {
if (cropYCenterOffsetPct > 1.0) {
throw new IllegalArgumentException("Value too large: Must be <= 1.0");
}
this.mCropYCenterOffsetPct = cropYCenterOffsetPct;
}
public float getCropXCenterOffsetPct() {
return mCropXCenterOffsetPct;
}
public void setCropXCenterOffsetPct(float cropXCenterOffsetPct) {
if (cropXCenterOffsetPct > 1.0) {
throw new IllegalArgumentException("Value too large: Must be <= 1.0");
}
this.mCropXCenterOffsetPct = cropXCenterOffsetPct;
}
private void myConfigureBounds() {
if (this.getScaleType() == ScaleType.MATRIX) {
/*
* Taken from Android's ImageView.java implementation:
*
* Excerpt from their source:
} else if (ScaleType.CENTER_CROP == mScaleType) {
mDrawMatrix = mMatrix;
float scale;
float dx = 0, dy = 0;
if (dwidth * vheight > vwidth * dheight) {
scale = (float) vheight / (float) dheight;
dx = (vwidth - dwidth * scale) * 0.5f;
} else {
scale = (float) vwidth / (float) dwidth;
dy = (vheight - dheight * scale) * 0.5f;
}
mDrawMatrix.setScale(scale, scale);
mDrawMatrix.postTranslate((int) (dx + 0.5f), (int) (dy + 0.5f));
}
*/
Drawable d = this.getDrawable();
if (d != null) {
int dwidth = d.getIntrinsicWidth();
int dheight = d.getIntrinsicHeight();
Matrix m = new Matrix();
int vwidth = getWidth() - this.getPaddingLeft() - this.getPaddingRight();
int vheight = getHeight() - this.getPaddingTop() - this.getPaddingBottom();
float scale;
float dx = 0, dy = 0;
if (dwidth * vheight > vwidth * dheight) {
float cropXCenterOffsetPct = mCropXCenterOffsetPct != null ?
mCropXCenterOffsetPct.floatValue() : 0.5f;
scale = (float) vheight / (float) dheight;
dx = (vwidth - dwidth * scale) * cropXCenterOffsetPct;
} else {
float cropYCenterOffsetPct = mCropYCenterOffsetPct != null ?
mCropYCenterOffsetPct.floatValue() : 0f;
scale = (float) vwidth / (float) dwidth;
dy = (vheight - dheight * scale) * cropYCenterOffsetPct;
}
m.setScale(scale, scale);
m.postTranslate((int) (dx + 0.5f), (int) (dy + 0.5f));
this.setImageMatrix(m);
}
}
}
// These 3 methods call configureBounds in ImageView.java class, which
// adjusts the matrix in a call to center_crop (android's built-in
// scaling and centering crop method). We also want to trigger
// in the same place, but using our own matrix, which is then set
// directly at line 588 of ImageView.java and then copied over
// as the draw matrix at line 942 of ImageVeiw.java
@Override
protected boolean setFrame(int l, int t, int r, int b) {
boolean changed = super.setFrame(l, t, r, b);
this.myConfigureBounds();
return changed;
}
@Override
public void setImageDrawable(Drawable d) {
super.setImageDrawable(d);
this.myConfigureBounds();
}
@Override
public void setImageResource(int resId) {
super.setImageResource(resId);
this.myConfigureBounds();
}
public void redraw() {
Drawable d = this.getDrawable();
if (d != null) {
// Force toggle to recalculate our bounds
this.setImageDrawable(null);
this.setImageDrawable(d);
}
}
}public class ImageViewTopCrop extends ImageView {
public ImageViewTopCrop(Context context) {
super(context);
setScaleType(ScaleType.MATRIX);
}
public ImageViewTopCrop(Context context, AttributeSet attrs) {
super(context, attrs);
setScaleType(ScaleType.MATRIX);
}
public ImageViewTopCrop(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
setScaleType(ScaleType.MATRIX);
}
@Override
protected boolean setFrame(int l, int t, int r, int b) {
computMatrix();
return super.setFrame(l, t, r, b);
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
computMatrix();
}
private void computMatrix() {
Matrix matrix = getImageMatrix();
float scaleFactor = getWidth() / (float) getDrawable().getIntrinsicWidth();
matrix.setScale(scaleFactor, scaleFactor, 0, 0);
setImageMatrix(matrix);
}}
onLayout为我省了很多钱！谢谢！我遇到了一个问题，它计算矩阵但不立即显示图像，并且添加onLayout代码解决了我的问题。
解决方案这里有两个问题：
这个小的修改解决了这个问题（将代码放置在onDraw中，并检查宽度和高度比例因子）：
@Override
protected void onDraw(Canvas canvas) {
Matrix matrix = getImageMatrix();
float scaleFactorWidth = getWidth() / (float) getDrawable().getIntrinsicWidth();
float scaleFactorHeight = getHeight() / (float) getDrawable().getIntrinsicHeight();
float scaleFactor = (scaleFactorWidth > scaleFactorHeight) ? scaleFactorWidth : scaleFactorHeight;
matrix.setScale(scaleFactor, scaleFactor, 0, 0);
setImageMatrix(matrix);
super.onDraw(canvas);
}最简单的解决方案：剪辑图像
@Override
public void draw(Canvas canvas) {
if(getWidth() > 0){
int clipHeight = 250;
canvas.clipRect(0,clipHeight,getWidth(),getHeight());
}
super.draw(canvas);
}