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/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.android.requestduringlayout;
import com.android.requestduringlayout.R;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.util.AttributeSet;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
/**
* This example shows what horrible things can result from calling requestLayout() during
* a layout pass. DON'T DO THIS.
*
* Watch the associated video for this demo on the DevBytes channel of developer.android.com
* or on YouTube at https://www.youtube.com/watch?v=HbAeTGoKG6k.
*/
public class RequestDuringLayout extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_request_during_layout);
final MyLayout myLayout = (MyLayout) findViewById(R.id.container);
Button addViewButton = (Button) findViewById(R.id.addView);
Button removeViewButton = (Button) findViewById(R.id.removeView);
Button forceLayoutButton = (Button) findViewById(R.id.forceLayout);
addViewButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
myLayout.mAddRequestPending = true;
myLayout.requestLayout();
}
});
removeViewButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
myLayout.mRemoveRequestPending = true;
myLayout.requestLayout();
}
});
forceLayoutButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
myLayout.requestLayout();
}
});
}
/**
* Custom layout to enable the convoluted way of requesting-during-layout that we're
* trying to show here. Yes, it's a hack. But it's a case that many apps hit (in much more
* complicated and less demoable ways), so it's interesting to at least understand the
* artifacts that come from this sequence of events.
*/
static class MyLayout extends LinearLayout {
int numButtons = 0;
boolean mAddRequestPending = false;
boolean mRemoveRequestPending = false;
public MyLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public MyLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyLayout(Context context) {
super(context);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
// Here is the root of the problem: we are adding/removing views during layout. This
// means that this view and its container will be put into an uncertain state that
// can be difficult to discover and recover from.
// Better approach: just add/remove at a time when layout is not running, certainly not
// in the middle of onLayout(), or other layout-associated logic.
if (mRemoveRequestPending) {
removeButton();
mRemoveRequestPending = false;
}
if (mAddRequestPending) {
addButton();
mAddRequestPending = false;
}
}
private void removeButton() {
if (getChildCount() > 1) {
removeViewAt(1);
}
}
private void addButton() {
Button button = new Button(getContext());
button.setLayoutParams(new LayoutParams(
LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
button.setText("Button " + (numButtons++));
addView(button);
}
}
}
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