6月3日，处理触摸事件，Android 开发，每日20行，第86天。

Box.java

package com.example.aster.draganddraw;

import android.graphics.PointF;

public class Box {
    private PointF mOrigin;
    private PointF mCurrent;

    public Box(PointF origin) {
        mOrigin = origin;
        mCurrent = origin;
    }

    public PointF getCurrent() {
        return mCurrent;
    }

    public void setCurrent(PointF current) {
        mCurrent = current;
    }

    public PointF getOrigin() {
        return mOrigin;
    }
}

BoxDrawingView.java

package com.example.aster.draganddraw;

import android.content.Context;
import android.graphics.PointF;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

import java.util.ArrayList;
import java.util.List;

public class BoxDrawingView extends View {
    private static final String TAG = "BoxDrawingView";

    private Box mCurrentBox;
    private List<Box> mBoxen = new ArrayList<>();

    // Used when creating the view in code
    public BoxDrawingView(Context context) {
        this(context, null);
    }

    // Used when inflating the view from XML
    public BoxDrawingView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        PointF current = new PointF(event.getX(), event.getY());
        String action = "";

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                action = "ACTION_DOWN";
                // Reset drawing state
                mCurrentBox = new Box(current);
                mBoxen.add(mCurrentBox);
                break;
            case MotionEvent.ACTION_MOVE:
                action = "ACTION_MOVE";
                if (mCurrentBox != null) {
                    mCurrentBox.setCurrent(current);
                    invalidate();
                }
                break;
            case MotionEvent.ACTION_UP:
                action = "ACTION_UP";
                mCurrentBox = null;
                break;
            case MotionEvent.ACTION_CANCEL:
                action = "ACTION_CANCEL";
                mCurrentBox = null;
                break;
        }

        Log.i(TAG, action + " at x=" + current.x + ", y=" + current.y);

        return true;
    }
}

DragAndDrawActivity.java

package com.example.aster.draganddraw;

import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class DragAndDrawActivity extends SingleFragmentActivity {

    @Override
    public Fragment createFragment() {
        return DragAndDrawFragment.newInstance();
    }
}

DragAndDrawFragment.java

package com.example.aster.draganddraw;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class DragAndDrawFragment extends Fragment {

    public static DragAndDrawFragment newInstance() {
        return new DragAndDrawFragment();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_drag_and_draw, container, false);
        return v;
    }
}

SingleFragmentActivity.java

package com.example.aster.draganddraw;

import android.os.Bundle;
import android.support.annotation.LayoutRes;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;

public abstract class SingleFragmentActivity extends AppCompatActivity {

    protected abstract Fragment createFragment();

    @LayoutRes
    protected int getLayoutResId() {
        return R.layout.activity_fragment;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(getLayoutResId());

        FragmentManager fm = getSupportFragmentManager();
        Fragment fragment = fm.findFragmentById(R.id.fragment_container);

        if (fragment == null) {
            fragment = createFragment();
            fm.beginTransaction().add(R.id.fragment_container, fragment).commit();
        }
    }
}

activity_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

fragment_drag_and_draw.xml

<?xml version="1.0" encoding="utf-8"?>
<com.example.aster.draganddraw.BoxDrawingView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />