java - Android Activity 方法使显示屏闪烁白色以发出警告通知

Question

我正在尝试让 Android Activity 闪烁，以向用户发出警告(全屏)。为了使其闪烁，我在 Activity 中插入了一个 ImageView，它的大小与显示器的大小相同，并且是白色的，这会将其可见性从可见旋转到消失。我曾研究过创建外部线程，但后来发现外部线程无法更改 UI 组件。我需要在 flash 更改之间暂停线程，这意味着我无法将其放在主 UI 线程上。我该如何实现这样的事情？

我在下面包含了一些代码:

XML

<ImageView
        android:id="@+id/alertScreen"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="gone"
        app:srcCompat="@android:color/white" />

Main.java

    public static boolean flashOn = false;
    public static boolean endFlash = false;
    public static Context context;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.aircraft_main);
        AircraftMain.context = getApplicationContext();

        flash = (Button) findViewById(R.id.flashTest);
        flash.setOnClickListener(flashBtnOnClickListener);
    }

    View.OnClickListener flashBtnOnClickListener = new View.OnClickListener() {
        @Override
        public void onClick(View arg0) {

            AsyncTask.execute(new Runnable() {
                public void run(){
                    AlertFlash alert = new AlertFlash(3);
                    alert.run();

                    ImageView v = findViewById(R.id.alertScreen);

                    while (endFlash != true) {
                        if(flashOn = true) {
                            v.setVisibility(View.VISIBLE);
                        } else {
                            v.setVisibility(View.GONE);
                        }
                    }
                }
            });

        }
    };

AlertFlash.java

public class AlertFlash implements Runnable {

    public static volatile int flashes;
    boolean suspendFlag, end;

    public AlertFlash (int flashNo) {
        flashes = flashNo * 2;
        suspendFlag = false;
        end = false;
    }

    public void run() {
        for (int i = 0; i<=flashes; i++) {

            if (suspendFlag = false) {
                AircraftMain.flashOn = true;
                suspendFlag = true;
            }
            else {
                AircraftMain.flashOn = false;
                suspendFlag = false;
            }

            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
        end = true;
    }
}

Answer 1

使用Activity.runOnUiThread() ，您可以从后台线程修改 UI 元素。

以下是针对您的情况我会采取的方法。在 Main.java 中，我首先创建一个简单的方法来修改传入 View 的可见性，特别是在 UI 线程上:

private void setViewVisibility(final View view, final int visibility) {
    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            view.setVisibility(visibility);
        }
    });
}

然后我会更改 while循环到以下内容:

while (endFlash != true) {
    if(flashOn = true) {
        setViewVisibility(v, View.VISIBLE);
    } else {
        setViewVisibility(v, View.GONE);
    }
}

编辑:为了防止 while 循环出现问题，我们可以通过传入 activity 来完全绕过它。和view创建 AlertFlash 时目的。见下文。

public class AlertFlash implements Runnable {

    public static volatile int flashes;
    boolean suspendFlag, end;

    private Activity activity;
    private View view;

    public AlertFlash (int flashNo, Activity activity, View view) {
        flashes = flashNo * 2;
        suspendFlag = false;
        end = false;

        this.activity = activity;
        this.view = view;
    }

    public void run() {
        for (int i = 0; i<=flashes; i++) {

            if (suspendFlag = false) {
                AircraftMain.flashOn = true;
                suspendFlag = true;
            }
            else {
                AircraftMain.flashOn = false;
                suspendFlag = false;
            }

            final int visibility = AircraftMain.flashOn ? View.VISIBLE : View.GONE;
            activity.runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    view.setVisibility(visibility);
                }
            });

            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
        end = true;
    }
}