android scrollto scrollby 扯一扯

标签：android

废话不多说，直接上思路－－－

1:试想一个界面，父布局是LinearLayout，竖直方向排列，然后里面添加两个View，如果我点击第一个View，直接调用第二个View的scrollTo或者scrollBy方法，第二个View会移动吗？给出代码和布局文件－－－－

布局文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical"
              android:background="#00ff00">
    <View
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:id="@+id/button1"
            android:background="#ff0000"/>
    <View
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:id="@+id/button2"
            android:background="#0000ff"/>
</LinearLayout>

public class ActivityText extends Activity implements View.OnClickListener {
	private View button1;
	private View button2;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_text);
		button1 = findViewById(R.id.button1);
		button2 = findViewById(R.id.button2);
		button1.setOnClickListener(this);
	}

	@Override
	public void onClick(View view) {
		if (view.getId() == R.id.button1) {
			//			button2.scrollBy(-30, -30);
			button2.scrollTo(30, 30);
		}
	}
}

我就开始想了，猜测－－是不是必须移动移动View的父容器，它里面的孩子才会移动？好，我就进行了下面的第二个实验－－

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical"
              android:background="#00ff00"
              android:id="@+id/ll">
    <View
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:id="@+id/button1"
            android:background="#ff0000"/>
    <View
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:id="@+id/button2"
            android:background="#0000ff"/>
</LinearLayout>

public class ActivityText extends Activity implements View.OnClickListener {
	private View button1;
	private View button2;
	private LinearLayout ll;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_text);
		ll = (LinearLayout) findViewById(R.id.ll);
		button1 = findViewById(R.id.button1);
		button2 = findViewById(R.id.button2);
		button1.setOnClickListener(this);
	}

	@Override
	public void onClick(View view) {
		if (view.getId() == R.id.button1) {
			ll.scrollBy(-30, -30);
		}
	}
}

查看ViewGroup的dispatchDraw()方法，发现一些蛛丝马迹－－－－

  int saveCount = 0;
2777        final boolean clipToPadding = (flags & CLIP_TO_PADDING_MASK) == CLIP_TO_PADDING_MASK;
2778        if (clipToPadding) {
2779            saveCount = canvas.save();
2780            canvas.clipRect(mScrollX + mPaddingLeft, mScrollY + mPaddingTop,
2781                    mScrollX + mRight - mLeft - mPaddingRight,
2782                    mScrollY + mBottom - mTop - mPaddingBottom);
2783
2784        }

布局文件：

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical"
              android:background="#00ff00"
              android:id="@+id/ll">
    <View
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:id="@+id/button1"
            android:background="#ff0000"/>
    <FrameLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#000000"
            android:id="@+id/fl">
        <View
                android:layout_width="200dp"
                android:layout_height="50dp"
                android:id="@+id/button2"
                android:background="#0000ff"/>
    </FrameLayout>
</LinearLayout>

public class ActivityText extends Activity implements View.OnClickListener {
	private View button1;
	private View button2;
	private LinearLayout ll;
	private FrameLayout fl;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_text);
		ll = (LinearLayout) findViewById(R.id.ll);
		fl = (FrameLayout) findViewById(R.id.fl);
		button1 = findViewById(R.id.button1);
		button2 = findViewById(R.id.button2);
		button1.setOnClickListener(this);
	}

	@Override
	public void onClick(View view) {
		if (view.getId() == R.id.button1) {
			fl.scrollBy(-30, -30);
		}
	}
}

读者可以自己实验以下，看一下效果－－－

android scrollto scrollby 扯一扯

标签：android

原文地址：http://blog.csdn.net/ly985557461/article/details/44957749