android 滚动视图（ScrollView）学习与应用

文章转自：http://www.javaeye.com/topic/149773

[c-sharp]
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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.scrollview.R;
/**
* Demonstrates wrapping a layout in a ScrollView.

*
*/
public class Scrollview extends Activity {

private static final String LOG_TAG =
"Scrollview";
private LinearLayout mLayout;

private ScrollView mScrollView;

private final Handler mHandler =
new Handler();

@Override
protected void onCreate(Bundle icicle) {

super.onCreate(icicle);
setContentView(R.layout.main);

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.setOnKeyListener(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(Scrollview.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(Scrollview.this);

buttonView.setText("Button " + mIndex++);

mLayout.addView(buttonView, p);
//改变默认焦点切换
buttonView.setOnKeyListener(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;

}
}
};
}

[c-sharp]
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<?xml version="1.0" encoding="utf-8"?>

<!-- Demonstrates scrolling with a ScrollView. -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:orientation="vertical">

<Button android:id="@+id/add_widget"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="增加按钮"/>

<ScrollView
android:id="@+id/scrollview"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:scrollbars="vertical">

<LinearLayout
android:id="@+id/layout"

android:orientation="vertical"

android:layout_width="fill_parent"

android:layout_height="wrap_content">

</LinearLayout>
</ScrollView>
</LinearLayout>

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

小结：

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。