[android] support pull down to dismiss pattern for ImageActivity

briar-android/src/main/java/org/briarproject/briar/android/conversation/ImageActivity.java

@@ -24,6 +24,7 @@ import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BriarActivity;
 import org.briarproject.briar.android.conversation.glide.GlideApp;
+import org.briarproject.briar.android.view.PullDownLayout;
 
 import static android.graphics.Color.TRANSPARENT;
 import static android.os.Build.VERSION.SDK_INT;
@@ -37,12 +38,14 @@ import static com.bumptech.glide.load.engine.DiskCacheStrategy.NONE;
 import static java.util.Objects.requireNonNull;
 import static org.briarproject.briar.android.util.UiUtils.formatDateAbsolute;
 
-public class ImageActivity extends BriarActivity {
+public class ImageActivity extends BriarActivity
+		implements PullDownLayout.Callback {
 
 	final static String ATTACHMENT = "attachment";
 	final static String NAME = "name";
 	final static String DATE = "date";
 
+	private PullDownLayout layout;
 	private AppBarLayout appBarLayout;
 
 	@Override
@@ -64,6 +67,9 @@ public class ImageActivity extends BriarActivity {
 
 		// inflate layout
 		setContentView(R.layout.activity_image);
+		layout = findViewById(R.id.layout);
+		layout.getBackground().setAlpha(255);
+		layout.setCallback(this);
 
 		// Status Bar
 		if (SDK_INT >= 21) {
@@ -142,6 +148,30 @@ public class ImageActivity extends BriarActivity {
 		}
 	}
 
+	@Override
+	public void onPullStart() {
+		appBarLayout.animate()
+				.alpha(0f)
+				.start();
+	}
+
+	@Override
+	public void onPull(float progress) {
+		layout.getBackground().setAlpha(Math.round((1 - progress) * 255));
+	}
+
+	@Override
+	public void onPullCancel() {
+		appBarLayout.animate()
+				.alpha(1f)
+				.start();
+	}
+
+	@Override
+	public void onPullComplete() {
+		supportFinishAfterTransition();
+	}
+
 	@RequiresApi(api = 16)
 	private void toggleSystemUi() {
 		View decorView = getWindow().getDecorView();

briar-android/src/main/java/org/briarproject/briar/android/view/PullDownLayout.java

@@ -0,0 +1,161 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 XiNGRZ <xxx@oxo.ooo>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package org.briarproject.briar.android.view;
+
+import android.content.Context;
+import android.support.annotation.Nullable;
+import android.support.v4.view.ViewCompat;
+import android.support.v4.widget.ViewDragHelper;
+import android.util.AttributeSet;
+import android.view.MotionEvent;
+import android.view.View;
+import android.view.ViewConfiguration;
+import android.widget.FrameLayout;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public class PullDownLayout extends FrameLayout {
+
+	private final ViewDragHelper dragger;
+
+	private final int minimumFlingVelocity;
+
+	@Nullable
+	private Callback callback;
+
+	public PullDownLayout(Context context) {
+		this(context, null);
+	}
+
+	public PullDownLayout(Context context, @Nullable AttributeSet attrs) {
+		this(context, attrs, 0);
+	}
+
+	public PullDownLayout(Context context, @Nullable AttributeSet attrs,
+			int defStyleAttr) {
+		super(context, attrs, defStyleAttr);
+		dragger = ViewDragHelper.create(this, 1f / 8f, new ViewDragCallback());
+		minimumFlingVelocity =
+				ViewConfiguration.get(context).getScaledMinimumFlingVelocity();
+	}
+
+	public void setCallback(@Nullable Callback callback) {
+		this.callback = callback;
+	}
+
+	@Override
+	public boolean onInterceptTouchEvent(MotionEvent ev) {
+		return dragger.shouldInterceptTouchEvent(ev);
+	}
+
+	@Override
+	public boolean onTouchEvent(MotionEvent event) {
+		dragger.processTouchEvent(event);
+		return true;
+	}
+
+	@Override
+	public void computeScroll() {
+		if (dragger.continueSettling(true)) {
+			ViewCompat.postInvalidateOnAnimation(this);
+		}
+	}
+
+	public interface Callback {
+
+		void onPullStart();
+
+		void onPull(float progress);
+
+		void onPullCancel();
+
+		void onPullComplete();
+
+	}
+
+	private class ViewDragCallback extends ViewDragHelper.Callback {
+
+		@Override
+		public boolean tryCaptureView(View child, int pointerId) {
+			return true;
+		}
+
+		@Override
+		public int clampViewPositionHorizontal(View child, int left, int dx) {
+			return 0;
+		}
+
+		@Override
+		public int clampViewPositionVertical(View child, int top, int dy) {
+			return Math.max(0, top);
+		}
+
+		@Override
+		public int getViewHorizontalDragRange(View child) {
+			return 0;
+		}
+
+		@Override
+		public int getViewVerticalDragRange(View child) {
+			return getHeight();
+		}
+
+		@Override
+		public void onViewCaptured(View capturedChild, int activePointerId) {
+			if (callback != null) {
+				callback.onPullStart();
+			}
+		}
+
+		@Override
+		public void onViewPositionChanged(View changedView, int left, int top,
+				int dx, int dy) {
+			if (callback != null) {
+				callback.onPull((float) top / (float) getHeight());
+			}
+		}
+
+		@Override
+		public void onViewReleased(View releasedChild, float xvel, float yvel) {
+			int slop = yvel > minimumFlingVelocity ? getHeight() / 6 :
+					getHeight() / 3;
+			if (releasedChild.getTop() > slop) {
+				if (callback != null) {
+					callback.onPullComplete();
+				}
+			} else {
+				if (callback != null) {
+					callback.onPullCancel();
+				}
+
+				dragger.settleCapturedViewAt(0, 0);
+				invalidate();
+			}
+		}
+
+	}
+
+}