一、ImageView简介
Android ImageView是一个用于显示图像的控件。它可以通过资源或bitmap对象加载图像。ImageView可以在应用程序中占据重要的位置,它可以显示应用程序的logo、产品图像、用户个人图像等。其使用非常广泛。
二、ImageView的属性
在使用ImageView时,我们经常需要设置一些属性来满足特定的需求。以下是一些常用属性。
1、android:src:指定ImageView要显示的图像资源的路径或url地址。
2、android:scaleType:指定如何显示图像。它分别有center、centerCrop、centerInside、fitCenter、fitEnd、fitStart、fitXY这几种显示方式。
3、android:tint:指定ImageView的着色颜色。
4、android:adjustViewBounds:设置ImageView是否根据图像大小调整视图界限。
三、ImageView的常见使用方法
1、使用本地资源文件
如果我们有本地的一张图片,需要在ImageView中进行展示,可以通过以下代码实现:
//在xml文件中设置 <ImageView android:id="@+id/image" android:layout_width="200dp" android:layout_height="200dp" android:layout_gravity="center" android:src="@drawable/image" /> //在java文件中设置 ImageView imageView = findViewById(R.id.image); imageView.setImageResource(R.drawable.image);
2、使用网络图片
我们也可以使用网络上的图片来展示。
//引入Glide库 dependencies { implementation 'com.github.bumptech.glide:glide:4.11.0' annotationProcessor 'com.github.bumptech.glide:compiler:4.9.0' } //在java文件中设置 ImageView imageView = findViewById(R.id.image); Glide.with(this).load("图片url").into(imageView);
3、使用圆形图片
有时我们会需要将图片设置成圆形。可以使用以下代码实现。
//创建CircleImageView类 public class CircleImageView extends ImageView { private static final ScaleType SCALE_TYPE = ScaleType.CENTER_CROP; private static final Bitmap.Config BITMAP_CONFIG = Bitmap.Config.ARGB_8888; private static final int COLORDRAWABLE_DIMENSION = 1; private static final int DEFAULT_BORDER_WIDTH = 0; private static final int DEFAULT_BORDER_COLOR = Color.BLACK; private static final int DEFAULT_FILL_COLOR = Color.TRANSPARENT; private final RectF mDrawableRect = new RectF(); private final RectF mBorderRect = new RectF(); private final Matrix mShaderMatrix = new Matrix(); private final Paint mBitmapPaint = new Paint(); private final Paint mBorderPaint = new Paint(); private final Paint mFillPaint = new Paint(); private int mBorderColor = DEFAULT_BORDER_COLOR; private int mBorderWidth = DEFAULT_BORDER_WIDTH; private int mFillColor = DEFAULT_FILL_COLOR; private Bitmap mBitmap; private BitmapShader mBitmapShader; private int mBitmapWidth; private int mBitmapHeight; private float mDrawableRadius; private float mBorderRadius; private boolean mReady; private boolean mSetupPending; public CircleImageView(Context context) { super(context); init(); } public CircleImageView(Context context, AttributeSet attrs) { this(context, attrs, 0); } public CircleImageView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.CircleImageView, defStyle, 0); mBorderWidth = a.getDimensionPixelSize(R.styleable.CircleImageView_border_width, DEFAULT_BORDER_WIDTH); mBorderColor = a.getColor(R.styleable.CircleImageView_border_color, DEFAULT_BORDER_COLOR); mFillColor = a.getColor(R.styleable.CircleImageView_fill_color, DEFAULT_FILL_COLOR); a.recycle(); init(); } private void init() { super.setScaleType(SCALE_TYPE); mReady = true; if (mSetupPending) { setup(); mSetupPending = false; } } @Override public ScaleType getScaleType() { return SCALE_TYPE; } @Override public void setScaleType(ScaleType scaleType) { if (scaleType != SCALE_TYPE) { throw new IllegalArgumentException(String.format("ScaleType %s not supported.", scaleType)); } } @Override public void setAdjustViewBounds(boolean adjustViewBounds) { if (adjustViewBounds) { throw new IllegalArgumentException("adjustViewBounds not supported."); } } @Override protected void onDraw(Canvas canvas) { if (mBitmap == null) { return; } canvas.drawCircle(getWidth() / 2, getHeight() / 2, mDrawableRadius, mFillPaint); canvas.drawCircle(getWidth() / 2, getHeight() / 2, mBorderRadius, mBorderPaint); canvas.drawCircle(getWidth() / 2, getHeight() / 2, mDrawableRadius, mBitmapPaint); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); setup(); } public int getBorderColor() { return mBorderColor; } public void setBorderColor(int borderColor) { if (borderColor == mBorderColor) { return; } mBorderColor = borderColor; mBorderPaint.setColor(mBorderColor); invalidate(); } public void setFillColor(int fillColor) { if (fillColor == mFillColor) { return; } mFillColor = fillColor; mFillPaint.setColor(fillColor); invalidate(); } public int getFillColor() { return mFillColor; } public int getBorderWidth() { return mBorderWidth; } public void setBorderWidth(int borderWidth) { if (borderWidth == mBorderWidth) { return; } mBorderWidth = borderWidth; setup(); } @Override public void setImageBitmap(Bitmap bm) { super.setImageBitmap(bm); mBitmap = bm; setup(); } @Override public void setImageDrawable(Drawable drawable) { super.setImageDrawable(drawable); mBitmap = getBitmapFromDrawable(drawable); setup(); } @Override public void setImageResource(int resId) { super.setImageResource(resId); mBitmap = getBitmapFromDrawable(getDrawable()); setup(); } @Override public void setImageURI(Uri uri) { super.setImageURI(uri); mBitmap = uri != null ? getBitmapFromDrawable(getDrawable()) : null; setup(); } private Bitmap getBitmapFromDrawable(Drawable drawable) { if (drawable == null) { return null; } if (drawable instanceof BitmapDrawable) { return ((BitmapDrawable) drawable).getBitmap(); } try { Bitmap bitmap; if (drawable instanceof ColorDrawable) { bitmap = Bitmap.createBitmap(COLORDRAWABLE_DIMENSION, COLORDRAWABLE_DIMENSION, BITMAP_CONFIG); } else { bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), BITMAP_CONFIG); } Canvas canvas = new Canvas(bitmap); drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight()); drawable.draw(canvas); return bitmap; } catch (Exception e) { e.printStackTrace(); return null; } } private void setup() { if (!mReady) { mSetupPending = true; return; } if (getWidth() == 0 && getHeight() == 0) { return; } if (mBitmap == null) { invalidate(); return; } mBitmapShader = new BitmapShader(mBitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP); mBitmapPaint.setAntiAlias(true); mBitmapPaint.setShader(mBitmapShader); mBorderPaint.setStyle(Paint.Style.STROKE); mBorderPaint.setAntiAlias(true); mBorderPaint.setColor(mBorderColor); mBorderPaint.setStrokeWidth(mBorderWidth); mFillPaint.setStyle(Paint.Style.FILL); mFillPaint.setAntiAlias(true); mFillPaint.setColor(mFillColor); mBitmapHeight = mBitmap.getHeight(); mBitmapWidth = mBitmap.getWidth(); mBorderRect.set(0, 0, getWidth(), getHeight()); mBorderRect.inset(mBorderWidth / 2, mBorderWidth / 2); mBorderRadius = Math.min((mBorderRect.height() - mBorderWidth) / 2, (mBorderRect.width() - mBorderWidth) / 2); mDrawableRect.set(mBorderRect); if (!mBorderRect.isEmpty()) { mDrawableRect.inset(mBorderWidth, mBorderWidth); } mDrawableRadius = Math.min(mDrawableRect.height() / 2, mDrawableRect.width() / 2); updateShaderMatrix(); invalidate(); } private void updateShaderMatrix() { float scale; float dx = 0; float dy = 0; mShaderMatrix.set(null); if (mBitmapWidth * mDrawableRect.height() > mDrawableRect.width() * mBitmapHeight) { scale = mDrawableRect.height() / (float) mBitmapHeight; dx = (mDrawableRect.width() - mBitmapWidth * scale) * 0.5f; } else { scale = mDrawableRect.width() / (float) mBitmapWidth; dy = (mDrawableRect.height() - mBitmapHeight * scale) * 0.5f; } mShaderMatrix.setScale(scale, scale); mShaderMatrix.postTranslate((int) (dx + 0.5f) + mDrawableRect.left, (int) (dy + 0.5f) + mDrawableRect.top); mBitmapShader.setLocalMatrix(mShaderMatrix); } }
在CircleImageView类中重写onDraw方法,绘制圆形图片,同时实现一些设置圆环等属性的方法。代码中定义了三个Paint对象,分别用于设置图片、边框和填充圆的属性。
4、使用Picasso加载图片
使用Picasso,可以简化应用中加载图片的过程。以下是使用Picasso的代码片段。
//引入Picasso库 dependencies { implementation 'com.squareup.picasso:picasso:2.71828' } //在java文件中设置 ImageView imageView = findViewById(R.id.image); Picasso.with(context).load("图片url").into(imageView);
5、Glide加载圆角图片
我们还可以使用Glide加载圆角图片。
//在java文件中设置 ImageView imageView = findViewById(R.id.image); Glide.with(this).load("图片url").apply(RequestOptions.bitmapTransform(new RoundedCorners(20))).into(imageView);
四、总结
本文主要介绍了Android ImageView控件的重要性以及使用方法。文章涵盖了设置本地资源文件、使用网络图片、使用圆形图片、使用Picasso加载图片和Glide加载圆角图片等几个方面。我们相信,通过本文的介绍,读者可以更好地了解ImageView控件,并且在应用中能够更好地使用ImageView控件。