Android音視訊學習(一)

摘要： 三種方式繪製: ImageView SurfaceView 自定義View 申請許可權 因為Android許可權機制, targetSdkVersion大於等於23(6.0)的應用, 在許可權方面需要注意動態獲取許可權, 我這裡做的比較簡單, 在on...

三種方式繪製:

• ImageView
• SurfaceView
• 自定義View

申請許可權

因為Android許可權機制, targetSdkVersion大於等於23(6.0)的應用, 在許可權方面需要注意動態獲取許可權, 我這裡做的比較簡單, 在onCreate方法裡申請 實際使用中不要像我這裡直接使用魔法值做requestCode...

AndroidManifest.xml

<!--從SDCard讀取資料許可權 -->
<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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比較簡單, 通過BitmapFactory.decodeFile方法獲取一張在內建儲存卡根目錄中的圖片

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也是經常用到的繪製方法, 優點比較多, 獨立執行緒繪製不影響主執行緒, 雙緩衝機制都是. 這裡是在初始化的回撥裡繪製準備好的Bitmap. 注意繪製前要lockCanvas, 繪製完要unlockAndPost

自定義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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自定義View也是經常用到的, 具體想了解自定義View的我推薦HenCoder系列的教程

總結

繪製的三種方式, 很基礎, 各有優勢, ImageView簡單好學, SurfaceView不阻塞主執行緒.