Android音视频学习(一)

三种方式绘制:

• ImageView
• SurfaceView
• 自定义View

申请权限

因为Android权限机制, targetSdkVersion大于等于23(6.0)的应用, 在权限方面需要注意动态获取权限, 我这里做的比较简单, 在onCreate方法里申请 实际使用中不要像我这里直接使用魔法值做requestCode...

AndroidManifest.xml

<!--  从SDCard读取数据权限 -->
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
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MainActivity:onCreate()

@Override
  protected void onCreate(Bundle savedInstanceState) {
    ...

    if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)
        != PackageManager.PERMISSION_GRANTED) {
      ActivityCompat.requestPermissions(this,
          new String[] { Manifest.permission.READ_EXTERNAL_STORAGE }, 1);
    } else {
      showPicture();
    }
  }
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MainActivity:onRequestPermissionResult()

@Override public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions,
      @NonNull int[] grantResults) {
    switch (requestCode) {
      case 1: {
        if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
          showPicture();
        }
        return;
      }
      default:
    }
  }
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ImageView

MainActivity:showPicture()

private void showPicture() {
    Bitmap bitmap = BitmapFactory.decodeFile(
        Environment.getExternalStorageDirectory().getPath() + File.separator + "11.jpg");
    mImageView.setImageBitmap(bitmap);
  }
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比较简单, 通过BitmapFactory.decodeFile方法获取一张在内置存储卡根目录中的图片

SurfaceView

MainActivity:showPicture()

private void showPicture() {
    mSurfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
      @Override public void surfaceCreated(SurfaceHolder holder) {
        if (holder == null) {
          return;
        }

        Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setStyle(Paint.Style.STROKE);

        Bitmap bitmap = BitmapFactory.decodeFile(
            Environment.getExternalStorageDirectory().getPath() + File.separator + "11.jpg");
        Canvas canvas = holder.lockCanvas();
        canvas.drawBitmap(bitmap, 0, 0, paint);
        holder.unlockCanvasAndPost(canvas);
      }

      @Override
      public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

      }

      @Override public void surfaceDestroyed(SurfaceHolder holder) {

      }
    });
  }
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Surface也是经常用到的绘制方法, 优点比较多, 独立线程绘制不影响主线程, 双缓冲机制都是. 这里是在初始化的回调里绘制准备好的Bitmap. 注意绘制前要lockCanvas, 绘制完要unlockAndPost

自定义View

MyView

public class MyView extends View {

  Paint mPaint;
  Bitmap mBitmap;

  public MyView(Context context) {
    super(context);
    init();
  }

  public MyView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  private void init() {
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mPaint.setStyle(Paint.Style.STROKE);
    mBitmap = BitmapFactory.decodeFile(
        Environment.getExternalStorageDirectory().getPath() + File.separator + "11.jpg");
  }

  @Override protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    if (mBitmap != null) {
      canvas.drawBitmap(mBitmap, 0, 0, mPaint);
    }
  }
}
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自定义View也是经常用到的, 具体想了解自定义View的我推荐HenCoder系列的教程

总结

绘制的三种方式, 很基础, 各有优势, ImageView简单好学, SurfaceView不阻塞主线程.