android - 在没有流行库的情况下在 Android 中拉动刷新

Question

我想在 Android 应用程序中实现下拉刷新，但我不想使用互联网上可用的下拉刷新库，因为它对于我正在使用的 gridView 来说太慢了。所以想自己动手实现，你知道怎么做吗？或者我应该从 GridView 使用哪些方法？

Answer 1

PullRefreshContainerView.java

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.TextView;

/**
 * A container for a ListView that can be pulled to refresh.
 * This will create a ListView and refresh header automatically, but you can
 * customize them by using {@link #setList(ListView)} and {@link #setRefreshHeader(View, int)}
 * <p>
 * To use, put this where you would normally put your ListView. Since this does not extend
 * ListView, you must use {@link #getList()} to modify the list or provide your own.
 * <p>
 * To get the actions of the list, use a {@link OnChangeStateListener} with {@link #setOnChangeStateListener(OnChangeStateListener)}.
 * If you want to change how the refresh header looks, you should do it during these state changes.   
 */
public class PullRefreshContainerView extends LinearLayout {    
    /**
     * Interface for listening to when the refresh container changes state.
     */
    public interface OnChangeStateListener {
        /**
         * Notifies a listener when the refresh view's state changes.
         * @param container The container that contains the header
         * @param state The state of the header. May be STATE_IDLE, STATE_READY,
         *      or STATE_REFRESHING.
         */
        public void onChangeState(PullRefreshContainerView container, int state);
    }

    /**
     * State of the refresh header when it is doing nothing or being pulled down slightly.
     */
    public static final int STATE_IDLE = 0;

    /**
     * State of the refresh header when it has been pulled down but not enough to start refreshing, and
     * has not yet been released.
     */
    public static final int STATE_PULL = 1;

    /**
     * State of the refresh header when it has been pulled down enough to start refreshing, but
     * has not yet been released.
     */
    public static final int STATE_RELEASE = 2;

    /**
     * State of the refresh header when the list should be refreshing.
     */
    public static final int STATE_LOADING = 3;

    private LinearLayout mHeaderContainer;
    private View mHeaderView;
    private ListView mList;
    private int mState;
    private OnChangeStateListener mOnChangeStateListener;

    private int REFRESH_VIEW_HEIGHT = 60;

    /**
     * Creates a new pull to refresh container.
     * 
     * @param context the application context
     */
    public PullRefreshContainerView(Context context) {
        super(context);
        init(context);
    }

    /**
     * Creates a new pull to refresh container.
     * 
     * @param context the application context
     * @param attrs the XML attribute set
     */
    public PullRefreshContainerView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    /**
     * Creates a new pull to refresh container.
     * 
     * @param context the application context
     * @param attrs the XML attribute set
     * @param defStyle the style for this view
     */
    public PullRefreshContainerView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs);
        init(context);
    }

    private void init(Context context) {
        mState = STATE_IDLE; // Start out as idle.

        float densityFactor = context.getResources().getDisplayMetrics().density;
        REFRESH_VIEW_HEIGHT *= densityFactor;

        // We don't want to see the fading edge on the container.
        setVerticalFadingEdgeEnabled(false);
        setVerticalScrollBarEnabled(false);

        setOrientation(LinearLayout.VERTICAL);

        // Set the default list and header.
        mHeaderContainer = new LinearLayout(context);
        addView(mHeaderContainer);
        setRefreshViewHeight(1);

        TextView headerView = new TextView(context);
        headerView.setText("Default refresh header.");
        setRefreshHeader(headerView);

        ListView list = new ListView(context);
        setList(list);
    }

    private boolean mScrollingList = true;
    private float mInterceptY;
    private int mLastMotionY;

    @Override
    public boolean dispatchTouchEvent (MotionEvent ev) {
        float oldLastY = mInterceptY;
        mInterceptY = ev.getY();

        if (mState == STATE_LOADING) {
            return super.dispatchTouchEvent(ev);
        }

        switch (ev.getAction()) {
        case MotionEvent.ACTION_DOWN:
            mLastMotionY = (int) ev.getY();
            mScrollingList = true;
            return super.dispatchTouchEvent(ev);

        case MotionEvent.ACTION_MOVE:
            if (mList.getFirstVisiblePosition() == 0
                    && (mList.getChildCount() == 0 || mList.getChildAt(0).getTop() == 0)) {
                if ((mInterceptY - oldLastY > 5) || (mState == STATE_PULL) || (mState == STATE_RELEASE)) {
                    mScrollingList = false;
                    applyHeaderHeight(ev);
                    return true;
                } else {
                    mScrollingList = true;
                    return super.dispatchTouchEvent(ev);
                }
            } else if (mScrollingList) {
                return super.dispatchTouchEvent(ev);
            } else {
                return super.dispatchTouchEvent(ev);
            }

        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_CANCEL:
            if (mState == STATE_RELEASE) {
                refresh();
            } else {
                changeState(STATE_IDLE);
            }

            if (mScrollingList) {
                return super.dispatchTouchEvent(ev);
            } else {
                return true;
            }

        default:
            return super.dispatchTouchEvent(ev);
        }
    }

    private void applyHeaderHeight(MotionEvent ev) {
        final int historySize = ev.getHistorySize();

        if (historySize > 0) {
            for (int h = 0; h < historySize; h++) {
                int historicalY = (int) (ev.getHistoricalY(h));
                updateRefreshView(historicalY - mLastMotionY);
            }
        } else {
            int historicalY = (int) ev.getY();
            updateRefreshView(historicalY - mLastMotionY);
        }
    }

    private void updateRefreshView(int height) {
        if (height <= 0) {
            return;
        }

        if ((REFRESH_VIEW_HEIGHT/4 <= mCurRefreshViewHeight) && (mCurRefreshViewHeight < REFRESH_VIEW_HEIGHT)) {
            setRefreshViewHeight(height);
            changeState(STATE_PULL);
        } else if (mCurRefreshViewHeight >= REFRESH_VIEW_HEIGHT) {
            if (height > REFRESH_VIEW_HEIGHT) {
                height = (int) (REFRESH_VIEW_HEIGHT + (height - REFRESH_VIEW_HEIGHT) *  REFRESH_VIEW_HEIGHT * 1.0f/height);
            }

            setRefreshViewHeight(height);
            changeState(STATE_RELEASE);
        } else {
            setRefreshViewHeight(height);
        }
    }

    private int mCurRefreshViewHeight = 60;
    private void setRefreshViewHeight(int height) {
        if (mCurRefreshViewHeight == height) {
            return;
        }

        if (height == 1) {
            mHeaderContainer.setLayoutParams(new LayoutParams(1, 1));
        } else {
            mHeaderContainer.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, height));
        }
        mCurRefreshViewHeight = height;
    }

    private void changeState(int state) {
        switch (state) {
        case STATE_IDLE:
            setRefreshViewHeight(1);
            break;
        case STATE_PULL:
            break;
        case STATE_RELEASE:
            break;
        case STATE_LOADING:
            setRefreshViewHeight(REFRESH_VIEW_HEIGHT);
            break;
        }

        mState = state;

        notifyStateChanged();
    }

    /**
     * Sets the list to be used in this pull to refresh container.
     * @param list the list to use
     */
    public void setList(ListView list) {
        if (mList != null) {
            removeView(mList);
        }
        mList = list;
        if (mList.getParent() != null) {
            ViewGroup parent = (ViewGroup) mList.getParent();
            parent.removeView(mList);
        }

        mList.setLayoutParams(new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
        addView(mList);
    }

    /**
     * @return the list inside this pull to refresh container
     */
    public ListView getList() {
        return mList;
    }

    /**
     * Sets the view to use as the refresh header. 
     * <p />
     * The header view is the view at the top that will show while the list
     * is refreshing. Usually, this will be a simple rectangle that says "refreshing" and the like.
     * <p />
     * 
     * @param headerView the view to use as the whole header.
     */
    public void setRefreshHeader(View header) {
        if (mHeaderView != null) {
            mHeaderContainer.removeView(mHeaderView);
        }       

        if (header == null) {
            throw new RuntimeException("Please supply a non-null header container.");
        }

        mHeaderContainer.addView(header, 0);
        mHeaderView = header;
    }

    public void refresh() { 
        changeState(STATE_LOADING);         
    }

    /**
     * Notifies the pull-to-refresh view that the refreshing is complete.
     * This will hide the refreshing header.
     */
    public void completeRefresh() {
        changeState(STATE_IDLE);
    }

    /**
     * Notifies the listener that the state has changed.
     */
    private void notifyStateChanged() {
        if (mOnChangeStateListener != null) {
            mOnChangeStateListener.onChangeState(this, mState);
        }
    }

    /**
     * @param listener the listener to be notified when the header state should change
     */
    public void setOnChangeStateListener(OnChangeStateListener listener) {
        mOnChangeStateListener = listener;
    }
}

如何使用UsageDemoActivity.java

import java.util.ArrayList;
import java.util.Timer;
import java.util.TimerTask;

import com.dmobile.pulltorefresh.PullRefreshContainerView.OnChangeStateListener;
import com.dmobile.pulltorefresh.R;

import android.app.Activity;
import android.os.Bundle;
import android.view.Gravity;
import android.view.ViewGroup.LayoutParams;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

public class UsageDemoActivity extends Activity {

    private PullRefreshContainerView mContainerView;
    private TextView mRefreshHeader;
    private ListView mList;

    private ArrayList<String> mStrings = new ArrayList<String>();
    private ArrayAdapter<String> mAdapter;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        mRefreshHeader = new TextView(this);
        mRefreshHeader.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
        mRefreshHeader.setGravity(Gravity.CENTER);
        mRefreshHeader.setText("Pull to refresh...");

        mContainerView = (PullRefreshContainerView) findViewById(R.id.container);
        mContainerView.setRefreshHeader(mRefreshHeader);

        mContainerView.setOnChangeStateListener(new OnChangeStateListener() {
            @Override
            public void onChangeState(PullRefreshContainerView container, int state) {
                switch (state) {
                case PullRefreshContainerView.STATE_IDLE:
                case PullRefreshContainerView.STATE_PULL:
                    mRefreshHeader.setText("Pull to refresh...");
                    break;
                case PullRefreshContainerView.STATE_RELEASE:
                    mRefreshHeader.setText("Release to refresh...");
                    break;
                case PullRefreshContainerView.STATE_LOADING:
                    mRefreshHeader.setText("Loading...");

                    final Timer t = new Timer();
                    t.schedule(new TimerTask() {

                        @Override
                        public void run() {
                            UsageDemoActivity.this.runOnUiThread(new Runnable() {
                                @Override
                                public void run() {

                                    addStrings(1);
                                    mContainerView.completeRefresh();
                                    t.cancel();
                                }
                            });
                        }
                    }, 5000, 5000);

                    break;
                }
            }
        });

        mList = mContainerView.getList();
        mAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mStrings);
        mList.setAdapter(mAdapter);

        addStrings(3);
    }

    private void addStrings(int count) {
        int curSize = mStrings.size();
        for (int i = 0; i < count; ++i) {
            mStrings.add("String " + (curSize + i));
        }

        mAdapter.notifyDataSetChanged();
    }
}

ma​​in.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >

    <com.dmobile.pulltorefresh.PullRefreshContainerView
        android:id="@+id/container"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"/>

</LinearLayout>

更新以使用 GRIDVIEWPullRefreshContainerView.java

private void init(Context context) {
        mState = STATE_IDLE; // Start out as idle.

    float densityFactor = context.getResources().getDisplayMetrics().density;
    REFRESH_VIEW_HEIGHT *= densityFactor;

    // We don't want to see the fading edge on the container.
    setVerticalFadingEdgeEnabled(false);
    setVerticalScrollBarEnabled(false);

    setOrientation(LinearLayout.VERTICAL);

    // Set the default list and header.
    mHeaderContainer = new LinearLayout(context);
    addView(mHeaderContainer);
    setRefreshViewHeight(1);

    TextView headerView = new TextView(context);
    headerView.setText("Default refresh header.");
    setRefreshHeader(headerView);

    GridView grid = new GridView(context);
    setList(grid);
}

并在 setListMethod();

中进行相关更改