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<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="300dp"
android:background="@color/gray"
android:hint="haha"
/>
</ScrollView>

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import android.app.Activity;
import android.os.Bundle;
import android.support.annotation.Nullable;
public class ScrollViewEditTextActivity extends Activity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.scroll_view_edit_text);
}
}

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@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
if (!mFillViewport) {
return;
}
//...ignore code

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@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int count = getChildCount();
//...ignore code
int maxHeight = 0;
int maxWidth = 0;
int childState = 0;
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (mMeasureAllChildren || child.getVisibility() != GONE) {
measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
//...ignore code

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@Override
protected void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed,
int parentHeightMeasureSpec, int heightUsed) {
final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
+ widthUsed, lp.width);
final int childHeightMeasureSpec = MeasureSpec.makeSafeMeasureSpec(
MeasureSpec.getSize(parentHeightMeasureSpec), MeasureSpec.UNSPECIFIED);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}

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@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//...ignore code
if (heightMode == MeasureSpec.EXACTLY) {
// Parent has told us how big to be. So be it.
height = heightSize;
mDesiredHeightAtMeasure = -1;
} else {
int desired = getDesiredHeight();
height = desired;
mDesiredHeightAtMeasure = desired;
if (heightMode == MeasureSpec.AT_MOST) {
height = Math.min(desired, heightSize);
}
}
int unpaddedHeight = height - getCompoundPaddingTop() - getCompoundPaddingBottom();
if (mMaxMode == LINES && mLayout.getLineCount() > mMaximum) {
unpaddedHeight = Math.min(unpaddedHeight, mLayout.getLineTop(mMaximum));
}
/*
* We didn't let makeNewLayout() register to bring the cursor into view,
* so do it here if there is any possibility that it is needed.
*/
if (mMovement != null ||
mLayout.getWidth() > unpaddedWidth ||
mLayout.getHeight() > unpaddedHeight) {
registerForPreDraw();
} else {
scrollTo(0, 0);
}
setMeasuredDimension(width, height);
}