android 滚动视图（ScrollView）学习与应用

首先总结一下andorid view的键盘事件处理过程：
键盘事件首先交给当前Activity中获得焦点的View，该View的setKeyListener(OnKeyListener l)中设定的l的onKey方法被调用,若返回true,framwork不再处理,否则有framework继续处理.我就是用该方法实现的智能焦点切换。

然后是自动滚动的实现，当ViewGroup中添加了新的View后,不能马上进行滚动,因为此时相应的高度信息还没有更新,需要用Handler来向消息队列投递一个Runnale来进行滚动。

相关实现如下:
1.ScrollView2.java

package com.google.android.samples.view;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.ScrollView;
import android.widget.TextView;

import com.google.android.samples.R;


/**
 * Demonstrates wrapping a layout in a ScrollView.
 *
 */
public class ScrollView2 extends Activity {
    private static final String LOG_TAG = "ScrollView2";
    private LinearLayout mLayout;
    private ScrollView mScrollView;
    private final Handler mHandler = new Handler();

    @Override
    protected void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.scroll_view_2);

        mLayout = (LinearLayout) findViewById(R.id.layout);
        mScrollView = (ScrollView) findViewById(R.id.scrollview);

        Button button = (Button) findViewById(R.id.add_widget);
        button.setOnClickListener(mClickListener);
        //改变默认焦点切换
        button.setKeyListener(mAddButtonKeyListener);
    }

    private Button.OnClickListener mClickListener = new Button.OnClickListener() {
        private int mIndex = 1;
        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            TextView textView = new TextView(ScrollView2.this);
            textView.setText("Text View " + mIndex);
            LinearLayout.LayoutParams p = new LinearLayout.LayoutParams(
                    LinearLayout.LayoutParams.FILL_PARENT,
                    LinearLayout.LayoutParams.WRAP_CONTENT
            );
            mLayout.addView(textView, p);

            Button buttonView = new Button(ScrollView2.this);
            buttonView.setText("Button " + mIndex++);
            mLayout.addView(buttonView, p);
            //改变默认焦点切换
            buttonView.setKeyListener(mNewButtonKeyListener);
            //投递一个消息进行滚动
            mHandler.post(mScrollToBottom);
        }
    };

    private Runnable mScrollToBottom = new Runnable() {
        @Override
        public void run() {
            // TODO Auto-generated method stub
            Log.d(LOG_TAG, "ScrollY: " + mScrollView.getScrollY());
            int off = mLayout.getMeasuredHeight() - mScrollView.getHeight();
            if (off > 0) {
                mScrollView.scrollTo(0, off);
            }
        }
    };

    private View.OnKeyListener mNewButtonKeyListener = new View.OnKeyListener() {
        public boolean onKey(View v, int keyCode, KeyEvent event) {
            if (keyCode == KeyEvent.KEYCODE_DPAD_DOWN &&
                    event.getAction() == KeyEvent.ACTION_DOWN &&
                    v == mLayout.getChildAt(mLayout.getChildCount() - 1)) {
                findViewById(R.id.add_widget).requestFocus();
                return true;
            }
            return false;
        }
    };

    private View.OnKeyListener mAddButtonKeyListener = new Button.OnKeyListener() {
        @Override
        public boolean onKey(View v, int keyCode, KeyEvent event) {
            // TODO Auto-generated method stub
            Log.d(LOG_TAG, event.toString());

            View viewToFoucus = null;
            if (event.getAction() == KeyEvent.ACTION_DOWN) {
                switch (keyCode) {
                case KeyEvent.KEYCODE_DPAD_UP:
                    int iCount = mLayout.getChildCount();
                    if ( iCount > 0) {
                        viewToFoucus = mLayout.getChildAt(iCount - 1);
                    }
                    break;
                case KeyEvent.KEYCODE_DPAD_DOWN:
                    if (mLayout.getChildCount() > 1) {
                        viewToFoucus = mLayout.getChildAt(1);
                    }
                    break;
                default:
                    break;
                }
            }

            if (viewToFoucus != null) {
                viewToFoucus.requestFocus();
                return true;
            } else {
                return false;
            }
        }
    };
}

2.scroll_view_2.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Demonstrates scrolling with a ScrollView. -->
<LinearLayout xmlns:android="http://schemas./apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">
    <Button id="@+id/add_widget"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Add Widget"/>
<ScrollView id="@+id/scrollview"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:scrollbars="vertical">
    <LinearLayout
        id="@+id/layout"
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content">
    </LinearLayout>
</ScrollView>
</LinearLayout>