Android
Disegno su tela con SurfaceView

Osservazioni

SurfaceView con il disegno del filo

Questo esempio descrive come creare un SurfaceView con un thread di disegno dedicato. Questa implementazione gestisce anche casi limite come problemi specifici di produzione e avvio / arresto del thread per risparmiare tempo CPU.

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
/**
* Defines a custom SurfaceView class which handles the drawing thread
**/
public class BaseSurface extends SurfaceView implements SurfaceHolder.Callback, View.OnTouchListener, Runnable
{

    /**
     * Holds the surface frame
     */
    private SurfaceHolder holder;

    /**
     * Draw thread
     */
    private Thread drawThread;

    /**
     * True when the surface is ready to draw
     */
    private boolean surfaceReady = false;


    /**
     * Drawing thread flag
     */

    private boolean drawingActive = false;

    /**
     * Paint for drawing the sample rectangle
     */
    private Paint samplePaint = new Paint();

    /**
     * Time per frame for 60 FPS
     */
    private static final int MAX_FRAME_TIME = (int) (1000.0 / 60.0);

    private static final String LOGTAG = "surface";    

    public BaseSurface(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        SurfaceHolder holder = getHolder();
        holder.addCallback(this);
        setOnTouchListener(this);

        // red
        samplePaint.setColor(0xffff0000);
        // smooth edges
        samplePaint.setAntiAlias(true);
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height)
    {
        if (width == 0 || height == 0)
        {
            return;
        }

        // resize your UI
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder)
    {
        this.holder = holder;

        if (drawThread != null)
        {
            Log.d(LOGTAG, "draw thread still active..");
            drawingActive = false;
            try
            {
                drawThread.join();
            } catch (InterruptedException e)
            { // do nothing
            }
        }

        surfaceReady = true;
        startDrawThread();
        Log.d(LOGTAG, "Created");
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder)
    {
        // Surface is not used anymore - stop the drawing thread
        stopDrawThread();
        // and release the surface
        holder.getSurface().release();

        this.holder = null;
        surfaceReady = false;
        Log.d(LOGTAG, "Destroyed");
    }

    @Override
    public boolean onTouch(View v, MotionEvent event)
    {
        // Handle touch events
        return true;
    }

    /**
     * Stops the drawing thread
     */
    public void stopDrawThread()
    {
        if (drawThread == null)
        {
            Log.d(LOGTAG, "DrawThread is null");
            return;
        }
        drawingActive = false;
        while (true)
        {
            try
            {
                Log.d(LOGTAG, "Request last frame");
                drawThread.join(5000);
                break;
            } catch (Exception e)
            {
                Log.e(LOGTAG, "Could not join with draw thread");
            }
        }
        drawThread = null;
    }

    /**
     * Creates a new draw thread and starts it.
     */
    public void startDrawThread()
    {
        if (surfaceReady && drawThread == null)
        {
            drawThread = new Thread(this, "Draw thread");
            drawingActive = true;
            drawThread.start();
        }
    }

    @Override
    public void run()
    {
        Log.d(LOGTAG, "Draw thread started");
        long frameStartTime;
        long frameTime;

        /*
         * In order to work reliable on Nexus 7, we place ~500ms delay at the start of drawing thread
         * (AOSP - Issue 58385)
         */
        if (android.os.Build.BRAND.equalsIgnoreCase("google") && android.os.Build.MANUFACTURER.equalsIgnoreCase("asus") && android.os.Build.MODEL.equalsIgnoreCase("Nexus 7"))
        {
            Log.w(LOGTAG, "Sleep 500ms (Device: Asus Nexus 7)");
            try
            {
                Thread.sleep(500);
            } catch (InterruptedException ignored)
            {
            }
        }
        try
        {
            while (drawingActive)
            {
                if (holder == null)
                {
                    return;
                }

                frameStartTime = System.nanoTime();
                Canvas canvas = holder.lockCanvas();
                if (canvas != null)
                {
                    // clear the screen using black
                    canvas.drawARGB(255, 0, 0, 0);

                    try
                    {
                        // Your drawing here
                        canvas.drawRect(0, 0, getWidth() / 2, getHeight() / 2, samplePaint);
                    } finally
                    {

                        holder.unlockCanvasAndPost(canvas);
                    }
                }

                // calculate the time required to draw the frame in ms
                frameTime = (System.nanoTime() - frameStartTime) / 1000000;

                if (frameTime < MAX_FRAME_TIME) // faster than the max fps - limit the FPS
                {
                    try
                    {
                        Thread.sleep(MAX_FRAME_TIME - frameTime);
                    } catch (InterruptedException e)
                    {
                        // ignore
                    }
                }
            }
        } catch (Exception e)
        {
            Log.w(LOGTAG, "Exception while locking/unlocking");
        }
        Log.d(LOGTAG, "Draw thread finished");
    }
}

Questo layout contiene solo il SurfaceView personalizzato e lo ingrandisce alle dimensioni dello schermo.

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

    <sample.devcore.org.surfaceviewsample.BaseSurface
        android:id="@+id/baseSurface"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</LinearLayout>

L'attività che utilizza SurfaceView è responsabile dell'avvio e dell'arresto del thread di disegno. Questo approccio consente di risparmiare batteria mentre il disegno viene interrotto non appena l'attività viene messa in background.

import android.app.Activity;
import android.os.Bundle;

public class MainActivity extends Activity
{

    /**
     * Surface object
     */
    private BaseSurface surface;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        surface = (BaseSurface) findViewById(R.id.baseSurface);
    }

    @Override
    protected void onResume()
    {
        super.onResume();
        // start the drawing
        surface.startDrawThread();
    }

    @Override
    protected void onPause()
    {
        // stop the drawing to save cpu time
        surface.stopDrawThread();
        super.onPause();
    }
}