如何从另一个线程做吐司（没有runOnUiThread）

Question

我需要从处理线程制作一个Android吐司，这是OpenCV的自定义，所以我不能使用这里建议的runOnUiThread（）：Android: Toast in a thread。

大部分代码来自CVCamera示例应用程序。但是那些不熟悉的，当我选择Surf菜单按钮时，SURFProcessor就像这样调用：

           else if (item.getTitle().equals("SURF")) {

                   defaultcallbackstack.addFirst(new SURFProcessor());
                   toasts(DIALOG_TUTORIAL_SURF, "");

           }

运行此处理器线程，以便当我按下手机的相机按钮（capturePress = true）时，将拍摄图像并完成处理。我想调用toasts方法如图所示：

class SURFProcessor implements NativeProcessor.PoolCallback {

           @Override
           public void process(int idx, image_pool pool, long timestamp,
                           NativeProcessor nativeProcessor) {
                   if(capturePress) {
                           String processMsg = processor.processFeatures(idx, pool, cvcamera.DETECT_SURF);
                           capturePress = false;
                           toasts(PROCESS_MESSAGE, processMsg);
                   }
           }
}

这是toasts方法，位于主类扩展Activity：

void toasts(int id, String msg) {
           switch (id) {
           case PROCESS_MESSAGE:
                   Toast.makeText(MMRapp.this, msg, Toast.LENGTH_LONG).show();
                   break;
.........

现在这段代码给了我一个错误：“无法在没有调用Looper.prepare（）的线程内创建处理程序。”如何调用toasts方法？或者是否可以让toasts方法监听processMsg中的更改？如果可能的话，我可以通过发送processMsg或改变类变量来实现。本质上，我需要从此处理器线程更新的字符串。

非常感谢，如果需要，我会提供更多信息/代码。 -Tom

Answer 1

使用处理程序和runnable在活动中创建Handler和runnable：

// these are members in the Activity class
Handler toastHandler = new Handler();
Runnable toastRunnable = new Runnable() {public void run() {Toast.makeText(Activity.this,...).show();}}

然后从你的线程使用中调用它

toastHandler.post(toastRunnable);

处理程序在创建它的线程中执行runnable。

Answer 2

使用符合您需求的过载。

/**
 * Muestra un toast sin necesidad de preocuparse de estar en el hilo de la
 * UI o no.
 *
 * @param mContext
 * @param sMessage
 */
public static void showToast(final Context mContext, final int nMessageId) {
    if (Utils.isUiThread()) {
        Toast.makeText(mContext.getApplicationContext(), nMessageId, Toast.LENGTH_LONG).show();
        return;
    }
    Runnable mRunnableToast = new Runnable() {
        @Override
        public void run() {
            Toast.makeText(mContext.getApplicationContext(), nMessageId, Toast.LENGTH_LONG).show();
        }
    };
    if (mContext instanceof Activity) {
        ((Activity) mContext).runOnUiThread(mRunnableToast);
        return;
    }
    Utils.runOnUiThread(mRunnableToast);
}

/**
 * Muestra un toast sin necesidad de preocuparse de estar en el hilo de la
 * UI o no.
 *
 * @param mContext
 * @param sMessage
 */
public static void showToast(final Context mContext, final CharSequence sMessage) {
    if (Utils.isUiThread()) {
        Toast.makeText(mContext.getApplicationContext(), sMessage, Toast.LENGTH_LONG).show();
        return;
    }
    Runnable mRunnableToast = new Runnable() {
        @Override
        public void run() {
            Toast.makeText(mContext.getApplicationContext(), sMessage, Toast.LENGTH_LONG).show();
        }
    };
    if (mContext instanceof Activity) {
        ((Activity) mContext).runOnUiThread(mRunnableToast);
        return;
    }
    Utils.runOnUiThread(mRunnableToast);
}

public static boolean isUiThread() {
    Looper mCurrentLooper = Looper.myLooper();
    if (mCurrentLooper == null) {
        return false;
    }
    if (mCurrentLooper.equals(Looper.getMainLooper())) {
        return true;
    }
    return false;
}

public static void runOnUiThread(Runnable mRunnable, Context mContext) {
    if (mContext instanceof Activity) {
        runOnUiThread(mRunnable, (Activity) mContext);
    } else {
        Utils.runOnUiThread(mRunnable);
    }
}

public static void runOnUiThread(Runnable mRunnable, View vView) {
    if (Utils.isUiThread()) {
        mRunnable.run();
    } else {
        vView.post(mRunnable);
    }
}

public static void runOnUiThread(Runnable mRunnable, Activity mActivity) {
    if (mActivity != null) {
        mActivity.runOnUiThread(mRunnable);
    } else {
        Utils.runOnUiThread(mRunnable);
    }
}

public static void runOnUiThread(Runnable mRunnable) {
    if (Utils.isUiThread()) {
        mRunnable.run();
    } else {
        Handler mUiHandler = new Handler(Looper.getMainLooper());
        mUiHandler.post(mRunnable);
    }
}

Answer 3

为什么不简单地使用广播接收器？ 写下来

public class ToastTrigger extends BroadcastReceiver {

    public static final String EXTRA_MESSAGE = "message";

    @Override
    public void onReceive(Context context, Intent intent) {
        Timber.d("ToastTrigger: received");
        if (intent.hasExtra(EXTRA_MESSAGE)) {
            Toast.makeText(context, intent.getStringExtra(EXTRA_MESSAGE), Toast.LENGTH_SHORT)
                .show();
        }
    }
}

定义它

    <receiver
        android:name=".receivers.ToastTrigger"
        android:enabled="true"
        android:exported="false">
        <intent-filter>
            <action android:name="com.example.TOAST" />
        </intent-filter>
    </receiver>

触发它

public void showMessage(String message) {
    Intent intent = new Intent();
    intent.setAction(getPackageName() + ".TOAST");
    intent.putExtra(ToastTrigger.EXTRA_MESSAGE, message);
    sendBroadcast(intent);
}