Android(安卓)ImageView、TextureView、自定义View显示图片

ImageView 显示图片

在 Android 平台上，显示图片的方式有很多种，其中最为简单的就是 ImageView。

1 . 在 lyaout 布局中，声明好 ImageView

android:id="@+id/image_view"android:layout_width="match_parent"android:layout_height="match_parent"android:scaleType="fitCenter"/>

2 . 在 Acitivity 中简单的使用

private ImageView mImageView;protected void onCreate(@Nullable Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.acitivity_imageview);    mImageView = findViewById(R.id.image_view);    mImageView.setImageResource(R.mipmap.images);}

SurfaceView 显示图片

SurfaceView 与普通的 view 的区别在于：

surfaceview 不需要在 UI 线程绘制，可以在子线程绘制
surfaceview 提供了双缓冲的机制，绘制效率高
surfaceview 是创建一个置于应用窗口之上的窗口，所以无法不能应用动画、变换和缩放，也没办法叠加

surfaceview 需要实现 SurfaceHolder.Callback 接口，包括三个声明周期

surfaceCreated(SurfaceHolder holder)surfaceChanged(SurfaceHolder holder, int format, int width, int height) surfaceDestroyed(SurfaceHolder holder)

具体的实现代码：

public class ImageSurfaceActivity extends AppCompatActivity implements SurfaceHolder.Callback {    private SurfaceView mSurfaceView;    private ExecutorService mThread;    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        mSurfaceView = new SurfaceView(this);        setContentView(mSurfaceView);        initSurfaceView();    }    private void initSurfaceView() {        // 创建一个只有一个线程的线程池，其实用Thread也可以        mThread = new ThreadPoolExecutor(1, 1, 2000L, TimeUnit.MILLISECONDS,                   new LinkedBlockingDeque());        // 添加SurfaceHolder.callback，在回调中可以绘制        mSurfaceView.getHolder().addCallback(this);    }    @Override    public void surfaceCreated(SurfaceHolder surfaceHolder) {        // 执行绘制        mThread.execute(new DrawRunnable());    }    @Override    public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {    }    @Override    public void surfaceDestroyed(SurfaceHolder surfaceHolder) {        if (!mThread.isShutdown()) {            mThread.shutdown();        }    }    private class DrawRunnable implements Runnable {        @Override        public void run() {            Bitmap bimap = BitmapFactory.decodeResource(ImageSurfaceActivity.this.getResources(),                            R.mipmap.images);            SurfaceHolder surfaceHolder = mSurfaceView.getHolder();            Canvas canvas = surfaceHolder.lockCanvas(); // 获取画布            Paint paint = new Paint();            Rect srcRect = new Rect(0, 0, bimap.getHeight(), bimap.getWidth());            Rect destRect = getBitmapRect(bimap);            canvas.drawBitmap(bimap, srcRect, destRect, paint);            surfaceHolder.unlockCanvasAndPost(canvas);        }    }    /**     * 图片的尺寸和屏幕的尺寸不一样，需要把图片调整居中     **/    private Rect getBitmapRect(Bitmap bimap) {        int bimapHeight = bimap.getHeight();        int bimapWidth = bimap.getWidth();        int viewWidth = mSurfaceView.getWidth();        int viewHeight = mSurfaceView.getHeight();        float bimapRatio = (float) bimapWidth / (float) bimapHeight; // 宽高比        float screenRatio = (float) viewWidth / (float) viewHeight;        int factWidth;        int factHeight;        int x1, y1, x2, y2;        if (bimapRatio > screenRatio) {            factWidth = viewWidth;            factHeight = (int)(factWidth / bimapRatio);            x1 = 0;            y1 = (viewHeight - factHeight) / 2;        } else if (bimapRatio < screenRatio) {            factHeight = viewHeight;            factWidth = (int)(factHeight * bimapRatio);            x1 = (viewWidth - factWidth) / 2;            y1 = 0;        } else {            factWidth = bimapWidth;            factHeight = bimapHeight;            x1 = 0;            y1 = 0;        }        x2 = x1 + factWidth;        y2 = y1 + factHeight;        return new Rect(x1, y1, x2, y2);    }}

自定义 View 显示图片

自定义 View 中有三个重要的声明周期：
onLayout() 布局
onMeasure() 测量
onDraw() 绘制
Android 的刷新间隔是 16ms

因为我们只是显示图片，不需要特别复杂的操作，只选取onDraw实现:

private void init() {    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);    mBitmap = BitmapFactory.decodeResource(getContext().getResources(), R.mipmap.images);}

@Overrideprotected void onDraw(Canvas canvas) {    super.onDraw(canvas);    Rect srcRect = new Rect(0, 0, mBitmap.getHeight(), mBitmap.getWidth());    Rect destRect = getBitmapRect(mBitmap); // 获取调整后的bitmap的显示位置    canvas.drawBitmap(mBitmap, srcRect, destRect, mPaint);}

ImageView 显示图片

SurfaceView 显示图片

自定义 View 显示图片

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