详解AndroidBitmap的使用

⼀ 图⽚表⽰原理

图⽚是由每个像素点来组成 像素点就是⼩⽅块图⽚的⼤⼩等于 宽*⾼*每个像素点的⼤⼩

⼆ 加载图⽚OOM异常

解决办法

其中big.jpg是⼀张21.2MB的⾼清图

public class MainActivity extends AppCompatActivity implements View.OnClickListener { ImageView mImageView;

@Override

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); findViewById(R.id.load).setOnClickListener(this); mImageView = findViewById(R.id.image); }

@Override

public void onClick(View view) { switch (view.getId()) { case R.id.load: load(); break; } }

private void load() { try {

BitmapFactory.Options option = new BitmapFactory.Options();

option.inJustDecodeBounds = true; //只会解析图⽚的⼤⼩ 不会加载图⽚的内容 BitmapFactory.decodeStream(getAssets().open(\"big.jpg\"), null, option); // 获取图⽚的宽⾼

int width = option.outWidth; int height = option.outHeight; // 获取屏幕的宽⾼

int screenWidth = getScreenWidth(); int screenHeight = getScreenHeight(); // 把图⽚的宽⾼和屏幕的宽⾼进⾏对⽐ int scaleX = width / screenWidth; int scaleY = height / screenHeight;

int scale = scaleX > scaleY ? scaleX : scaleY;

option.inJustDecodeBounds = false; //加载图⽚的内容

// 如果设置为>1 请求解码器对原始数据进⾏⼦采样 例如inSampleSize==4返回图像的宽度/⾼度是原始图像的1/4 // 任何值<=1都与1相同

option.inSampleSize = scale;

Bitmap bitmap = BitmapFactory.decodeStream(getAssets().open(\"big.jpg\"), null, option); int byteCount = bitmap.getByteCount();

Log.i(\"HUANG\ mImageView.setImageBitmap(bitmap); } catch (IOException e) { e.printStackTrace(); } }

/** 得到设备屏幕的宽度 (像素) **/ private int getScreenWidth() {

return getResources().getDisplayMetrics().widthPixels; }

/** 得到设备屏幕的⾼度 (像素) **/

private int getScreenHeight() {

return getResources().getDisplayMetrics().heightPixels; }}

三 图⽚处理原理

Android⾥⾯所有的显⽰效果都是绘制出来的⽤Android封装好的绘图类去绘制图⽚Canvas: 画布Paint: 画笔

Matrix: 图形矩阵 3*3Bitmap: 要绘制的图⽚

四 图⽚的旋转 平移 缩放

其中mm.jpg是⼀张57KB的图 属于正常范围 不需要额外处理

public class MainActivity extends AppCompatActivity implements View.OnClickListener { ImageView mImageView, mCopyView; Bitmap mBitmap;

@Override

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);

findViewById(R.id.change).setOnClickListener(this); mImageView = findViewById(R.id.image); mCopyView = findViewById(R.id.copy); try {

mBitmap = BitmapFactory.decodeStream(getAssets().open(\"mm.jpg\")); mImageView.setImageBitmap(mBitmap); } catch (IOException e) { e.printStackTrace(); } }

@Override

public void onClick(View view) { switch (view.getId()) { case R.id.change: change(); break; } }

// 图⽚的旋转 平移 缩放

// 注意: 旋转 平移 缩放 这三种效果在本案例中只能同时存在⼀种 分别打开注释看效果 private void change() {

if (null == mBitmap) return;

// 新建空⽩的图⽚ 要和原图的⼤⼩⼀样

Bitmap bitmap = Bitmap.createBitmap(mBitmap.getWidth(), mBitmap.getHeight(), mBitmap.getConfig()); Canvas canvas = new Canvas(bitmap); //画布 传参必须是⼀个空⽩的图⽚ 否则报错 Paint paint = new Paint(); //画笔 Matrix matrix = new Matrix(); //矩阵 // 旋转30度 以图⽚的中⼼为圆⼼

matrix.setRotate(30, mBitmap.getWidth() / 2, mBitmap.getHeight() / 2); // X轴平移80

//matrix.setTranslate(80, 0); // Y轴缩为原来的0.5

//matrix.setScale(1F, 0.5F, mBitmap.getWidth() / 2, mBitmap.getHeight() / 2); canvas.drawColor(Color.WHITE); //绘制背景为⽩⾊

canvas.drawBitmap(mBitmap, matrix, paint); //绘制图⽚ mCopyView.setImageBitmap(bitmap); }

}

五 图⽚的涂鸦操作

其中mm.jpg是⼀张57KB的图 属于正常范围 不需要额外处理

public class MainActivity extends AppCompatActivity implements View.OnTouchListener { ImageView mImageView; Bitmap mNewBitmap; Canvas mCanvas; Paint mPaint; Matrix mMatrix;

int mStartX, mStartY; //按下点的坐标

@Override

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);

mImageView = findViewById(R.id.image); try {

Bitmap bitmap = BitmapFactory.decodeStream(getAssets().open(\"mm.jpg\")); // 不能直接在原图上进⾏绘制 必须新建空⽩的图⽚

mNewBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig()); mCanvas = new Canvas(mNewBitmap); mPaint = new Paint();

mPaint.setColor(Color.YELLOW); mMatrix = new Matrix();

// 把原图绘制在空⽩的图⽚上

mCanvas.drawBitmap(bitmap, mMatrix, mPaint); mImageView.setImageBitmap(mNewBitmap);

mImageView.setOnTouchListener(this); //设置触摸监听 } catch (IOException e) { e.printStackTrace(); } }

@Override

public boolean onTouch(View v, MotionEvent event) { switch (event.getAction()) {

case MotionEvent.ACTION_DOWN: //按下 mStartX = (int) event.getX(); mStartY = (int) event.getY(); break;

case MotionEvent.ACTION_MOVE: //移动 // 获取移动点的坐标

int moveX = (int) event.getX(); int moveY = (int) event.getY(); // 画线

mCanvas.drawLine(mStartX, mStartY, moveX, moveY, mPaint); // 把新图设置给ImageView

mImageView.setImageBitmap(mNewBitmap); // 把移动点置为开始点 mStartX = moveX; mStartY = moveY; break;

case MotionEvent.ACTION_UP: //弹起 break; }

return true; //事件⾃⼰来处理 }}

六 图⽚的颜⾊处理

图⽚是有颜⾊核⼼原理就是重绘图⽚

改变图⽚的颜⾊就是对画笔进⾏操

其中mm.jpg是⼀张57KB的图 属于正常范围 不需要额外处理

public class MainActivity extends AppCompatActivity implements View.OnClickListener { ImageView mImageView;

Bitmap mBitmap, mNewBitmap; Canvas mCanvas; Paint mPaint;

@Override

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);

mImageView = findViewById(R.id.image); try {

mBitmap = BitmapFactory.decodeStream(getAssets().open(\"mm.jpg\")); mImageView.setImageBitmap(mBitmap);

mNewBitmap = Bitmap.createBitmap(mBitmap.getWidth(), mBitmap.getHeight(), mBitmap.getConfig()); mCanvas = new Canvas(mNewBitmap); mPaint = new Paint();

findViewById(R.id.change).setOnClickListener(this); } catch (IOException e) { e.printStackTrace(); } }

@Override

public void onClick(View view) { switch (view.getId()) { case R.id.change:

int randomR = (int) (Math.random() * 256); //0-255 随机数 int randomG = (int) (Math.random() * 256); //0-255 随机数 int randomB = (int) (Math.random() * 256); //0-255 随机数 int randomA = (int) (Math.random() * 256); //0-255 随机数 float colorR = (255 - randomR) / (float) 255; float colorG = (255 - randomG) / (float) 255; float colorB = (255 - randomB) / (float) 255; float colorA = (255 - randomA) / (float) 255; Log.i(\"HUANG\ Log.i(\"HUANG\ Log.i(\"HUANG\ Log.i(\"HUANG\ Log.i(\"HUANG\ Log.i(\"HUANG\ Log.i(\"HUANG\ Log.i(\"HUANG\

ColorMatrix matrix = new ColorMatrix(); //颜⾊矩阵 5*4 matrix.set(new float[]{ colorR, 0, 0, 0, 0, //red 0, colorG, 0, 0, 0, //green 0, 0, colorB, 0, 0, //blue 0, 0, 0, colorA, 0 //alpha });

ColorMatrixColorFilter filter = new ColorMatrixColorFilter(matrix); mPaint.setColorFilter(filter);

mCanvas.drawBitmap(mBitmap, new Matrix(), mPaint); mImageView.setImageBitmap(mNewBitmap); break; } }}

七 内存泄漏和内存溢出

内存泄漏(MemoryLeak)

有些对象只有有限的⽣命周期 当它们的任务完成之后 它们将被回收 如果在对象的⽣命周期本该结束的时候 这个对象还被⼀系列的引⽤ 这就会导致内存泄漏

随着泄漏的累积 App将消耗完内存 内存泄漏最终会导致内存溢出内存泄漏的原因

1. 资源对象没关闭(Cursor File...)

2. 没有及时调⽤recycle()释放不再使⽤的Bitmap3. ⼴播注册没取消4. ...

内存溢出(OutOfMemoryError OOM)

内存溢出是指当对象的内存占⽤已经超出分配内存的空间⼤⼩内存溢出的原因1. Bitmap过⼤2. 内存泄露导致3. ...

⼋ ImageView中scaleType属性值含义

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