java - 如何在 Android 中向左滑动按钮

Question

这是我的第一个问题，如果格式有点错误，我深表歉意。

我目前正在 Android Studio 中开发一个项目，我需要动态制作一个向左滑动的按钮(就像在 iPhone 的“邮件”中看到的那样)。我知道这里发布了很多关于刷卡的问题，但我找不到任何具体回答我问题的内容。我在下面发布了我的代码。任何帮助将非常感激。如果您需要更多信息，请告诉我。

public class ViewHistoryActivity extends ActionBarActivity {
   //list holding the pre-sorted logs stored in database
   private ArrayList<WorkoutLog> logHistory;
   private GestureDetectorCompat gd;

   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_view_history);
      logHistory = new ArrayList<WorkoutLog>();
      // Create database handler. This allows easy interaction with
      // the app's database.
      DatabaseHandler db = new DatabaseHandler(this);
      // Get sorted (by date) ArrayList of WorkoutLogs.
      logHistory = (ArrayList<WorkoutLog>) db.getAllWorkoutLogs();
      //loop that creates buttons based on the number of logs stored in the database
      //these buttons will be scrollable because of the xml file. Clicking on a button will
      //bring you to another activity in which you can see the contents of the log
      for (int i==0; i<logHistory.size(); i++) {
         //new button being created for log
         Button myButton = new Button(this);
         //set the text of the log to be the logs title (will add date later)
         myButton.setText(logHistory.get(i).getLogTitle() + "\n" + logHistory.get(i).getLogDateString() + "\n\n\n");
         //needed because logHistory was complaining below for intent.putExtra(...)
         final int test = i;
         //allows user to click on it
         myButton.setClickable(true);
         //when the button is click on by the user, starts the new activity with the detailed
         //log information.  Right now, when clicked on the log just returns to the main page
         myButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
               Intent intent = new Intent(ViewHistoryActivity.this, ViewHistoryDetailed.class);
           intent.putExtra("logID",String.valueOf(logHistory.get(test).getLogID()));
                startActivity(intent);
            }
        });
        myButton.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                gd = new GestureDetectorCompat(ViewHistoryActivity.this, new MyGestureListener());
                gd.onTouchEvent(event);
                return true;
            }
            class MyGestureListener extends GestureDetector.SimpleOnGestureListener {
                //private static final String DEBUG_TAG = "Gestures";
                private static final int SWIPE_THRESHOLD = 100;
                private static final int SWIPE_VELOCITY_THRESHOLD = 100;

                public boolean onDown(MotionEvent event) {
                    Toast.makeText(ViewHistoryActivity.this, "got to onDown", Toast.LENGTH_SHORT).show();
                    return true;
                }
                public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
                    Toast.makeText(ViewHistoryActivity.this, "Got to here", Toast.LENGTH_SHORT).show();
                    boolean result = false;
                    try {
                        float diffY = e2.getY() - e1.getY();
                        float diffX = e2.getX() - e1.getX();
                        if (Math.abs(diffX) > Math.abs(diffY)) {
                           if (Math.abs(diffX) > SWIPE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                              if (diffX > 0) {
                                 onSwipeRight();
                              } else {
                                  // onSwipeLeft();
                              }
                           }
                           result = true;
                        } else if (Math.abs(diffY) > SWIPE_THRESHOLD && Math.abs(velocityY) > SWIPE_VELOCITY_THRESHOLD) {
                            if (diffY > 0) {
                               // onSwipeBottom();
                            } else {
                               // onSwipeTop();
                            }
                        }
                        result = true;
                    } catch (Exception exception) {
                        exception.printStackTrace();
                    }
                    return result;
                }
                public void onSwipeRight() {
                    Toast.makeText(ViewHistoryActivity.this, "Caught swipe left", Toast.LENGTH_SHORT).show();
                }
            }
        });

        //gets the layout of this class, which has been nested inside a scrollable interface
        LinearLayout layout = (LinearLayout) findViewById(R.id.View_History);
        //sets button parameters
        LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
        //adds button to the layout
        layout.addView(myButton, lp);
    }
}

现在，每当我点击向下时，它都会给我一条 Toast 消息，“onDown 被点击”。但每当我尝试 throw 时，它什么也没做——我没有收到任何消息。

Answer 1

您需要在 onCreate 中初始化您的 GestureDetectorCompat (gd)，而不是每次发生 onTouch 事件时。

尝试将下面的代码移动到 onCreate

gd = new GestureDetectorCompat(ViewHistoryActivity.this, new MyGestureListener());

GestureDetector 保留对所有不同MotionEvents(向下、移动、向上)的引用，以便它可以计算 throw 的移动和速度。如果每次事件发生时它都被初始化，它将永远无法计算 MotionEvents 的完整序列(仅最后一个 MotionEvent)