前言

在Android音视频开发中，网上知识点过于零碎，自学起来难度非常大，不过音视频大牛Jhuster提出了《Android 音视频从入门到提高 - 任务列表》。本文是Android音视频任务列表的第一篇， 对应的要学习的内容是：在Android平台绘制一张图片，使用至少3种不同的 API，ImageView，SurfaceView，自定义View。

音视频任务列表

音视频任务列表: 点击此处跳转查看.

（一）ImageView绘制图片

（1）将图片分别放入mipmap-hdpi、assets

（2）布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/iv_picture"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    </ImageView>

</LinearLayout>

（3）代码：

// ImageView加载几种来源：
// (1)drawable/mipmap中通过R.drawabe.xxx加载图片资源
// (2)assests路径的资源

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ImageView customImageView = findViewById(R.id.iv_picture);
        // 方式一：drawable/mipmap中通过R.drawabe.xxx加载图片资源
        // customImageView.setBackgroundResource(R.mipmap.wuqian);

        // 方式二：加载assests路径的资源
        customImageView.setImageBitmap(getImageFromAssetsFile(this, "lilangdi.jpg"));
    }

    public static Bitmap getImageFromAssetsFile(Context context, String fileName) {
        Bitmap image = null;
        AssetManager am = context.getResources().getAssets();
        try {
            InputStream is = am.open(fileName);
            image = BitmapFactory.decodeStream(is);
            is.close();
        } catch(IOException e) {
            e.printStackTrace();
        }
        return image;
    }

}

（4）结果：

（二）SurfaceView绘制图片

（1）将图片放入手机文件夹内

（2）布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <SurfaceView
        android:id="@+id/sv_drawpicture"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </SurfaceView>

</LinearLayout>

（3）添加权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

（4）代码：

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        verifyStoragePermissions(this);
        setContentView(R.layout.activity_main);

        SurfaceView mSurfaceView = findViewById(R.id.sv_drawpicture);

        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);

                // 方式一：Environment.getExternalStorageDirectory().getPath()获取路径为:/storage/emulated/0
                // File.separator得到的是：/
                Bitmap bitmap = BitmapFactory.decodeFile(Environment.getExternalStorageDirectory().getPath() + File.separator + "wuqian.jpg");  // 获取bitmap

                // 方式二：
                // Bitmap bitmap = BitmapFactory.decodeFile("/storage/emulated/0/wuqian.jpg"); // 获取bitmap

                Canvas canvas = holder.lockCanvas();  // 先锁定当前surfaceView的画布
                canvas.drawBitmap(bitmap, 0, 0, paint); //执行绘制操作
                holder.unlockCanvasAndPost(canvas); // 解除锁定并显示在界面上
            }

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

            }

            @Override
            public void surfaceDestroyed(SurfaceHolder holder) {

            }
        });

    }
    
    private static final int REQUEST_EXTERNAL_STORAGE = 1;
    private static String[] PERMISSIONS_STORAGE = {
            "android.permission.READ_EXTERNAL_STORAGE",
            "android.permission.WRITE_EXTERNAL_STORAGE" };

    public static void verifyStoragePermissions(Activity activity) {
        try {
            // 检测是否有写的权限
            int permission = ActivityCompat.checkSelfPermission(activity,
                    "android.permission.WRITE_EXTERNAL_STORAGE");
            if (permission != PackageManager.PERMISSION_GRANTED) {
                // 没有写的权限，去申请写的权限，会弹出对话框
                ActivityCompat.requestPermissions(activity, PERMISSIONS_STORAGE,REQUEST_EXTERNAL_STORAGE);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

（5）结果：

（三） 自定义View绘制图片

（1）将图片放入手机或者放入mipmap-hdpi

（2）布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.lzacking.viewdemo.CustomView
        android:id="@+id/customview"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </com.lzacking.viewdemo.CustomView>

</LinearLayout>

（3）添加权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

（4）代码：

CustomView：

public class CustomView extends View {

    Paint paint = new Paint();
    Bitmap bitmap;

    public CustomView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        paint.setAntiAlias(true);
        paint.setStyle(Paint.Style.STROKE);
        // 方式一：从手机读取图片
        bitmap = BitmapFactory.decodeFile(Environment.getExternalStorageDirectory().getPath() + File.separator + "kugou.png");  // 获取bitmap

        // 方式二：从mipmap-hdpi读取图片
        // bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.taylor);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // 不建议在onDraw做任何分配内存的操作
        if (bitmap != null) {
            canvas.drawBitmap(bitmap, 0, 0, paint);
        }
    }

}

MainActivity：

// 方式一：从手机读取图片
// 方式二：从mipmap-hdpi读取图片
public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // 如果从手机读取图片，则需要申请权限
        verifyStoragePermissions(this);
        setContentView(R.layout.activity_main);
    }

    private static final int REQUEST_EXTERNAL_STORAGE = 1;
    private static String[] PERMISSIONS_STORAGE = {
            "android.permission.READ_EXTERNAL_STORAGE",
            "android.permission.WRITE_EXTERNAL_STORAGE" };

    public static void verifyStoragePermissions(Activity activity) {
        try {
            // 检测是否有写的权限
            int permission = ActivityCompat.checkSelfPermission(activity,
                    "android.permission.WRITE_EXTERNAL_STORAGE");
            if (permission != PackageManager.PERMISSION_GRANTED) {
                // 没有写的权限，去申请写的权限，会弹出对话框
                ActivityCompat.requestPermissions(activity, PERMISSIONS_STORAGE,REQUEST_EXTERNAL_STORAGE);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

（5）结果：