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。
目录
<?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>
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（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;
}
}
<?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>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
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();
}
}
}
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（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>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
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();
}
}
}
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