android – LinearyLayout一旦高度为0就不会调整大小

我在LinearLayout中有一个LinearLayout.我想使用动画来调整孩子的大小(有时候我会使用动画片).这是我的布局XML.

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

    <LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="vertical">
        <!-- Lots more controls will appear above -->
        <LinearLayout android:layout_width="fill_parent" android:layout_height="0dp" android:id="@+id/animation_subject">
            <TextView
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:text="@string/hello"
                android:gravity="center" />
        </LinearLayout> 
        <!-- Lots more controls will appear below -->
    </LinearLayout>

    <Button android:text="Slide it Down!" android:layout_width="fill_parent" android:layout_height="wrap_content" android:onClick="btnDoAnimDown_OnClick" />

</LinearLayout>

现在,正如您所看到的,有一个按钮,这是该按钮的代码.

public void btnDoAnimDown_OnClick(View v)
{
    View pnlSlider = findViewById(R.id.animation_subject);
    pnlSlider.measure(1000,1000);
    DropDownAnim anim = new DropDownAnim(pnlSlider,pnlSlider.getMeasuredHeight(),true);
    anim.setDuration(2000);
    pnlSlider.startAnimation(anim);

    return;     
}

如果你现在运行它,它不会滑下来.完全没有.但是,如果您要将Button移动到我已命名为Overview的LinearLayout并将其放在Child LinearLayout之后,那么它就可以了！像这样…

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

    <LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="vertical">
        <!-- Lots more controls will appear above -->
        <LinearLayout android:layout_width="fill_parent" android:layout_height="0dp" android:id="@+id/animation_subject">
            <TextView
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:text="@string/hello"
                android:gravity="center" />
        </LinearLayout> 
        <!-- Lots more controls will appear below -->
        <Button android:text="Slide it Down!" android:layout_width="fill_parent" android:layout_height="wrap_content" android:onClick="btnDoAnimDown_OnClick" />
    </LinearLayout>

</LinearLayout>

它现在滑下来,正如预期的那样.显然,父布局会发生一些事情…因为getMeasuredHeight()返回正确的值,所以动画实际上并没有运行！

这是动画类,我错过了什么傻事？可能是我！

import android.util.Log;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.Transformation;

public class DropDownAnim extends Animation {
    int targetHeight;
    View view;
    boolean down;

    public DropDownAnim(View view,int targetHeight,boolean down) {
        this.view = view;
        this.targetHeight = targetHeight;
        this.down = down;
    }

    @Override
    protected void applyTransformation(float interpolatedTime,Transformation t) {
        int newHeight;
        if (down) {
            newHeight = (int) (targetHeight * interpolatedTime);
        } else {
            newHeight = (int) (targetHeight * (1 - interpolatedTime));
        }
        Log.d("new height",String.valueOf(newHeight));
        view.getLayoutParams().height = newHeight;
        view.requestLayout();
    }

    @Override
    public void initialize(int width,int height,int parentWidth,int parentHeight) {
        super.initialize(width,height,((View)view.getParent()).getWidth(),parentHeight);
    }

    @Override
    public boolean willChangeBounds() {
        return true;
    }
}

任何帮助都会很棒！