1 files changed, 131 insertions, 0 deletions
diff --git a/samples/devbytes/ui/RequestDuringLayout/src/com/example/android/requestduringlayout/RequestDuringLayout.java b/samples/devbytes/ui/RequestDuringLayout/src/com/example/android/requestduringlayout/RequestDuringLayout.java
new file mode 100644
index 000000000..e6f22cf16
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+++ b/samples/devbytes/ui/RequestDuringLayout/src/com/example/android/requestduringlayout/RequestDuringLayout.java
@@ -0,0 +1,131 @@
+/*
+ * 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);
+        }
+
+    }
+
+}