Android 从不同 class 访问 canvas

Question

我需要访问我从另一个 class 创建的 canvas。

所以我有一个 class 延伸 LinearLayout 绘图弧。

现在从 main activity 我需要访问这个 canvas 它被绘制并重绘。最好只有一部分。

这里有一些代码被剥离到主要部分。

ArchProgressBar.java（带canvas的那个）

public class ArchProgressBar extends LinearLayout {

    public ArchProgressBar(Context context, AttributeSet attrs) {

    private void init(Context context) {
        this.setWillNotDraw(false);
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        inflater.inflate(R.layout.arch_progress_bar, this, true);
        this.postInvalidate();
    }

    static void drawMeCircle(int aka) {

    }

    @Override
    public void onDraw(Canvas canvas) {

        int mPaintHex = 0xFFFFFFFF;
        int mPaintColor = Color.argb(100, Color.red(mPaintHex), Color.green(mPaintHex), Color.blue(mPaintHex));

        float left = 295;
        float top = 712;
        float right = 788;
        float bottom = 1208;

        Paint mPaintBackground = new Paint();
        mPaintBackground.setAntiAlias(true);
        mPaintBackground.setStyle(Paint.Style.STROKE);
        mPaintBackground.setStrokeWidth(13);
        mPaintBackground.setColor(mPaintColor);

        RectF mRectF = new RectF(left, top, right, bottom);

        // THIS IS BACKGROUND LINE! draw background line
        canvas.drawArc(mRectF, START_ANGLE, ARCH_LENGTH, false, mPaintBackground);

        int mHourHex = 0xFF00FF00;
        int mHourColor = Color.argb(255, Color.red(mHourHex), Color.green(mHourHex), Color.blue(mHourHex));

        Paint mPaintHours = new Paint();
        mPaintHours.setAntiAlias(true);
        mPaintHours.setStyle(Paint.Style.STROKE);
        mPaintHours.setStrokeWidth(13);
        mPaintHours.setColor(mHourColor);

        RectF mRectH = new RectF(left, top, right, bottom);

        // THIS IS HOUR LINE!draw hour line
        Calendar hCal = Calendar.getInstance();
        int hHour = hCal.get(Calendar.HOUR);
        if(hHour != 0) {
            for(int i=0; i<hHour-1; i++){
                canvas.drawArc(mRectH, START_ANGLE + ARCH_LENGTH + (i*30) +2, ARCH_LENGTH, false, mPaintHours);
            }
        }
    }

HomeActivity.java 主要 activity 应用程序（扩展 Activity）

public class HomeActivity extends Activity {

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

        IntentFilter mIntentFilter = new IntentFilter();
        mIntentFilter.addAction(Intent.ACTION_TIME_TICK);
        mIntentFilter.addAction(Intent.ACTION_TIMEZONE_CHANGED);
        mIntentFilter.addAction(Intent.ACTION_TIME_CHANGED);
        registerReceiver(m_timeChangedReceiver, mIntentFilter);
    }
    //clock thing start
    private final BroadcastReceiver m_timeChangedReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            final String action = intent.getAction();
                Calendar hCal = Calendar.getInstance();
                int hHour = hCal.get(Calendar.HOUR);
                ArchProgressBar.drawMeCircle(1);
        }
    };

    public void showApps(View v){
        Intent i = new Intent(this, AppsListActivity.class);
        startActivity(i);
    }
}

现在当 BroadcastRecieved 被触发时，我想访问 ArchProgressBar 的 canvas，删除 hour line（或者如果不可能删除整个内容，只删除那部分) 并在其上重新绘制一些新内容。

如果你正在徘徊 drawMeCircle。这只是我在玩的东西。包括在内以展示我认为它必须如何工作。

Answer 1

您只需更改视图对象中的一些值并调用 invalidate() 即可获得您需要的内容。这将尽快重绘 canvas 。关于你的代码，我建议以这种方式修改它（假设你的视图有一个 id = @+id/arch_progress_bar）

HomeActivity

private final BroadcastReceiver m_timeChangedReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        final String action = intent.getAction();
        Calendar hCal = Calendar.getInstance();
        int hHour = hCal.get(Calendar.HOUR);
        ArchProgressBar bar = (ArchProgressBar) findViewById(R.id.arch_progress_bar);
        if (bar != null) {
            bar.drawMeCircle(1);
        }
    }
};

// remember to unregister the broadcast receiver in your onDestroy()
// as further optimization, you can also move the findViewById inside your onCreate(), so you don't have to repeat it for every broadcast you get

ArchProgressBar

pubic void drawMeCircle(int aka) {
     // your business logic
     invalidate();
}   // Remove the static keyword, it's not necessary

最后考虑：由于显示旋转，您应该注意 activity 娱乐。要处理这种情况，您应该在 onSaveInstanceState() activity 回调期间保存从广播接收器获得的值（本例中为 1？），通过作为 onCreate 参数获得的包检索它并将其重新设置为您的视图。

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