Java tutorial
/* * Copyright (C) 2015 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 android.support.percent; import android.content.Context; import android.content.res.TypedArray; import android.support.annotation.NonNull; import android.support.v4.view.MarginLayoutParamsCompat; import android.support.v4.view.ViewCompat; import android.util.AttributeSet; import android.util.Log; import android.view.View; import android.view.ViewGroup; import android.support.percent.R; /** * Helper for layouts that want to support percentage based dimensions. * * <p>This class collects utility methods that are involved in extracting percentage based dimension * attributes and applying them to ViewGroup's children. If you would like to implement a layout * that supports percentage based dimensions, you need to take several steps: * * <ol> * <li> You need a {@link ViewGroup.LayoutParams} subclass in your ViewGroup that implements * {@link android.support.percent.PercentLayoutHelper.PercentLayoutParams}. * <li> In your {@code LayoutParams(Context c, AttributeSet attrs)} constructor create an instance * of {@link PercentLayoutHelper.PercentLayoutInfo} by calling * {@link PercentLayoutHelper#getPercentLayoutInfo(Context, AttributeSet)}. Return this * object from {@code public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo()} * method that you implemented for {@link android.support.percent.PercentLayoutHelper.PercentLayoutParams} interface. * <li> Override * {@link ViewGroup.LayoutParams#setBaseAttributes(TypedArray, int, int)} * with a single line implementation {@code PercentLayoutHelper.fetchWidthAndHeight(this, a, * widthAttr, heightAttr);} * <li> In your ViewGroup override {@link ViewGroup#generateLayoutParams(AttributeSet)} to return * your LayoutParams. * <li> In your {@link ViewGroup#onMeasure(int, int)} override, you need to implement following * pattern: * <pre class="prettyprint"> * protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { * mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec); * super.onMeasure(widthMeasureSpec, heightMeasureSpec); * if (mHelper.handleMeasuredStateTooSmall()) { * super.onMeasure(widthMeasureSpec, heightMeasureSpec); * } * } * </pre> * <li>In your {@link ViewGroup#onLayout(boolean, int, int, int, int)} override, you need to * implement following pattern: * <pre class="prettyprint"> * protected void onLayout(boolean changed, int left, int top, int right, int bottom) { * super.onLayout(changed, left, top, right, bottom); * mHelper.restoreOriginalParams(); * } * </pre> * </ol> */ public class PercentLayoutHelper { private static final String TAG = "PercentLayout"; private static final boolean DEBUG = false; private static final boolean VERBOSE = false; private final ViewGroup mHost; public PercentLayoutHelper(@NonNull ViewGroup host) { if (host == null) { throw new IllegalArgumentException("host must be non-null"); } mHost = host; } /** * Helper method to be called from {@link ViewGroup.LayoutParams#setBaseAttributes} override * that reads layout_width and layout_height attribute values without throwing an exception if * they aren't present. */ public static void fetchWidthAndHeight(ViewGroup.LayoutParams params, TypedArray array, int widthAttr, int heightAttr) { params.width = array.getLayoutDimension(widthAttr, 0); params.height = array.getLayoutDimension(heightAttr, 0); } /** * Iterates over children and changes their width and height to one calculated from percentage * values. * @param widthMeasureSpec Width MeasureSpec of the parent ViewGroup. * @param heightMeasureSpec Height MeasureSpec of the parent ViewGroup. */ public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec) { if (DEBUG) { Log.d(TAG, "adjustChildren: " + mHost + " widthMeasureSpec: " + View.MeasureSpec.toString(widthMeasureSpec) + " heightMeasureSpec: " + View.MeasureSpec.toString(heightMeasureSpec)); } // Calculate available space, accounting for host's paddings int widthHint = View.MeasureSpec.getSize(widthMeasureSpec) - mHost.getPaddingLeft() - mHost.getPaddingRight(); int heightHint = View.MeasureSpec.getSize(heightMeasureSpec) - mHost.getPaddingTop() - mHost.getPaddingBottom(); for (int i = 0, N = mHost.getChildCount(); i < N; i++) { View view = mHost.getChildAt(i); ViewGroup.LayoutParams params = view.getLayoutParams(); if (DEBUG) { Log.d(TAG, "should adjust " + view + " " + params); } if (params instanceof PercentLayoutParams) { PercentLayoutInfo info = ((PercentLayoutParams) params).getPercentLayoutInfo(); if (DEBUG) { Log.d(TAG, "using " + info); } if (info != null) { if (params instanceof ViewGroup.MarginLayoutParams) { info.fillMarginLayoutParams(view, (ViewGroup.MarginLayoutParams) params, widthHint, heightHint); } else { info.fillLayoutParams(params, widthHint, heightHint); } } } } } /** * Constructs a PercentLayoutInfo from attributes associated with a View. Call this method from * {@code LayoutParams(Context c, AttributeSet attrs)} constructor. */ public static PercentLayoutInfo getPercentLayoutInfo(Context context, AttributeSet attrs) { PercentLayoutInfo info = null; TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.PercentLayout_Layout); float value = array.getFraction(R.styleable.PercentLayout_Layout_layout_widthPercent, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "percent width: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.widthPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_heightPercent, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "percent height: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.heightPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginPercent, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "percent margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.leftMarginPercent = value; info.topMarginPercent = value; info.rightMarginPercent = value; info.bottomMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginLeftPercent, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "percent left margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.leftMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginTopPercent, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "percent top margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.topMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginRightPercent, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "percent right margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.rightMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginBottomPercent, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "percent bottom margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.bottomMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginStartPercent, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "percent start margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.startMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginEndPercent, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "percent end margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.endMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_aspectRatio, 1, 1, -1f); if (value != -1f) { if (VERBOSE) { Log.v(TAG, "aspect ratio: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.aspectRatio = value; } array.recycle(); if (DEBUG) { Log.d(TAG, "constructed: " + info); } return info; } /** * Iterates over children and restores their original dimensions that were changed for * percentage values. Calling this method only makes sense if you previously called * {@link PercentLayoutHelper#adjustChildren(int, int)}. */ public void restoreOriginalParams() { for (int i = 0, N = mHost.getChildCount(); i < N; i++) { View view = mHost.getChildAt(i); ViewGroup.LayoutParams params = view.getLayoutParams(); if (DEBUG) { Log.d(TAG, "should restore " + view + " " + params); } if (params instanceof PercentLayoutParams) { PercentLayoutInfo info = ((PercentLayoutParams) params).getPercentLayoutInfo(); if (DEBUG) { Log.d(TAG, "using " + info); } if (info != null) { if (params instanceof ViewGroup.MarginLayoutParams) { info.restoreMarginLayoutParams((ViewGroup.MarginLayoutParams) params); } else { info.restoreLayoutParams(params); } } } } } /** * Iterates over children and checks if any of them would like to get more space than it * received through the percentage dimension. * * If you are building a layout that supports percentage dimensions you are encouraged to take * advantage of this method. The developer should be able to specify that a child should be * remeasured by adding normal dimension attribute with {@code wrap_content} value. For example * he might specify child's attributes as {@code app:layout_widthPercent="60%p"} and * {@code android:layout_width="wrap_content"}. In this case if the child receives too little * space, it will be remeasured with width set to {@code WRAP_CONTENT}. * * @return True if the measure phase needs to be rerun because one of the children would like * to receive more space. */ public boolean handleMeasuredStateTooSmall() { boolean needsSecondMeasure = false; for (int i = 0, N = mHost.getChildCount(); i < N; i++) { View view = mHost.getChildAt(i); ViewGroup.LayoutParams params = view.getLayoutParams(); if (DEBUG) { Log.d(TAG, "should handle measured state too small " + view + " " + params); } if (params instanceof PercentLayoutParams) { PercentLayoutInfo info = ((PercentLayoutParams) params).getPercentLayoutInfo(); if (info != null) { if (shouldHandleMeasuredWidthTooSmall(view, info)) { needsSecondMeasure = true; params.width = ViewGroup.LayoutParams.WRAP_CONTENT; } if (shouldHandleMeasuredHeightTooSmall(view, info)) { needsSecondMeasure = true; params.height = ViewGroup.LayoutParams.WRAP_CONTENT; } } } } if (DEBUG) { Log.d(TAG, "should trigger second measure pass: " + needsSecondMeasure); } return needsSecondMeasure; } private static boolean shouldHandleMeasuredWidthTooSmall(View view, PercentLayoutInfo info) { int state = ViewCompat.getMeasuredWidthAndState(view) & ViewCompat.MEASURED_STATE_MASK; return state == ViewCompat.MEASURED_STATE_TOO_SMALL && info.widthPercent >= 0 && info.mPreservedParams.width == ViewGroup.LayoutParams.WRAP_CONTENT; } private static boolean shouldHandleMeasuredHeightTooSmall(View view, PercentLayoutInfo info) { int state = ViewCompat.getMeasuredHeightAndState(view) & ViewCompat.MEASURED_STATE_MASK; return state == ViewCompat.MEASURED_STATE_TOO_SMALL && info.heightPercent >= 0 && info.mPreservedParams.height == ViewGroup.LayoutParams.WRAP_CONTENT; } /* package */ static class PercentMarginLayoutParams extends ViewGroup.MarginLayoutParams { // These two flags keep track of whether we're computing the LayoutParams width and height // in the fill pass based on the aspect ratio. This allows the fill pass to be re-entrant // as the framework code can call onMeasure() multiple times before the onLayout() is // called. Those multiple invocations of onMeasure() are not guaranteed to be called with // the same set of width / height. private boolean mIsHeightComputedFromAspectRatio; private boolean mIsWidthComputedFromAspectRatio; public PercentMarginLayoutParams(int width, int height) { super(width, height); } } /** * Container for information about percentage dimensions and margins. It acts as an extension * for {@code LayoutParams}. */ public static class PercentLayoutInfo { /** The decimal value of the percentage-based width. */ public float widthPercent; /** The decimal value of the percentage-based height. */ public float heightPercent; /** The decimal value of the percentage-based left margin. */ public float leftMarginPercent; /** The decimal value of the percentage-based top margin. */ public float topMarginPercent; /** The decimal value of the percentage-based right margin. */ public float rightMarginPercent; /** The decimal value of the percentage-based bottom margin. */ public float bottomMarginPercent; /** The decimal value of the percentage-based start margin. */ public float startMarginPercent; /** The decimal value of the percentage-based end margin. */ public float endMarginPercent; /** The decimal value of the percentage-based aspect ratio. */ public float aspectRatio; /* package */ final PercentMarginLayoutParams mPreservedParams; public PercentLayoutInfo() { widthPercent = -1f; heightPercent = -1f; leftMarginPercent = -1f; topMarginPercent = -1f; rightMarginPercent = -1f; bottomMarginPercent = -1f; startMarginPercent = -1f; endMarginPercent = -1f; mPreservedParams = new PercentMarginLayoutParams(0, 0); } /** * Fills the {@link ViewGroup.LayoutParams#width} and {@link ViewGroup.LayoutParams#height} * fields of the passed {@link ViewGroup.LayoutParams} object based on currently set * percentage values. */ public void fillLayoutParams(ViewGroup.LayoutParams params, int widthHint, int heightHint) { // Preserve the original layout params, so we can restore them after the measure step. mPreservedParams.width = params.width; mPreservedParams.height = params.height; // We assume that width/height set to 0 means that value was unset. This might not // necessarily be true, as the user might explicitly set it to 0. However, we use this // information only for the aspect ratio. If the user set the aspect ratio attribute, // it means they accept or soon discover that it will be disregarded. final boolean widthNotSet = (mPreservedParams.mIsWidthComputedFromAspectRatio || mPreservedParams.width == 0) && (widthPercent < 0); final boolean heightNotSet = (mPreservedParams.mIsHeightComputedFromAspectRatio || mPreservedParams.height == 0) && (heightPercent < 0); if (widthPercent >= 0) { params.width = (int) (widthHint * widthPercent); } if (heightPercent >= 0) { params.height = (int) (heightHint * heightPercent); } if (aspectRatio >= 0) { if (widthNotSet) { params.width = (int) (params.height * aspectRatio); // Keep track that we've filled the width based on the height and aspect ratio. mPreservedParams.mIsWidthComputedFromAspectRatio = true; } if (heightNotSet) { params.height = (int) (params.width / aspectRatio); // Keep track that we've filled the height based on the width and aspect ratio. mPreservedParams.mIsHeightComputedFromAspectRatio = true; } } if (DEBUG) { Log.d(TAG, "after fillLayoutParams: (" + params.width + ", " + params.height + ")"); } } /** * @deprecated Use * {@link #fillMarginLayoutParams(View, ViewGroup.MarginLayoutParams, int, int)} * for proper RTL support. */ @Deprecated public void fillMarginLayoutParams(ViewGroup.MarginLayoutParams params, int widthHint, int heightHint) { fillMarginLayoutParams(null, params, widthHint, heightHint); } /** * Fills the margin fields of the passed {@link ViewGroup.MarginLayoutParams} object based * on currently set percentage values and the current layout direction of the passed * {@link View}. */ public void fillMarginLayoutParams(View view, ViewGroup.MarginLayoutParams params, int widthHint, int heightHint) { fillLayoutParams(params, widthHint, heightHint); // Preserve the original margins, so we can restore them after the measure step. mPreservedParams.leftMargin = params.leftMargin; mPreservedParams.topMargin = params.topMargin; mPreservedParams.rightMargin = params.rightMargin; mPreservedParams.bottomMargin = params.bottomMargin; MarginLayoutParamsCompat.setMarginStart(mPreservedParams, MarginLayoutParamsCompat.getMarginStart(params)); MarginLayoutParamsCompat.setMarginEnd(mPreservedParams, MarginLayoutParamsCompat.getMarginEnd(params)); if (leftMarginPercent >= 0) { params.leftMargin = (int) (widthHint * leftMarginPercent); } if (topMarginPercent >= 0) { params.topMargin = (int) (heightHint * topMarginPercent); } if (rightMarginPercent >= 0) { params.rightMargin = (int) (widthHint * rightMarginPercent); } if (bottomMarginPercent >= 0) { params.bottomMargin = (int) (heightHint * bottomMarginPercent); } boolean shouldResolveLayoutDirection = false; if (startMarginPercent >= 0) { MarginLayoutParamsCompat.setMarginStart(params, (int) (widthHint * startMarginPercent)); shouldResolveLayoutDirection = true; } if (endMarginPercent >= 0) { MarginLayoutParamsCompat.setMarginEnd(params, (int) (widthHint * endMarginPercent)); shouldResolveLayoutDirection = true; } if (shouldResolveLayoutDirection && (view != null)) { // Force the resolve pass so that start / end margins are propagated to the // matching left / right fields MarginLayoutParamsCompat.resolveLayoutDirection(params, ViewCompat.getLayoutDirection(view)); } if (DEBUG) { Log.d(TAG, "after fillMarginLayoutParams: (" + params.width + ", " + params.height + ")"); } } @Override public String toString() { return String.format( "PercentLayoutInformation width: %f height %f, margins (%f, %f, " + " %f, %f, %f, %f)", widthPercent, heightPercent, leftMarginPercent, topMarginPercent, rightMarginPercent, bottomMarginPercent, startMarginPercent, endMarginPercent); } /** * Restores the original dimensions and margins after they were changed for percentage based * values. You should call this method only if you previously called * {@link PercentLayoutHelper.PercentLayoutInfo#fillMarginLayoutParams(View, ViewGroup.MarginLayoutParams, int, int)}. */ public void restoreMarginLayoutParams(ViewGroup.MarginLayoutParams params) { restoreLayoutParams(params); params.leftMargin = mPreservedParams.leftMargin; params.topMargin = mPreservedParams.topMargin; params.rightMargin = mPreservedParams.rightMargin; params.bottomMargin = mPreservedParams.bottomMargin; MarginLayoutParamsCompat.setMarginStart(params, MarginLayoutParamsCompat.getMarginStart(mPreservedParams)); MarginLayoutParamsCompat.setMarginEnd(params, MarginLayoutParamsCompat.getMarginEnd(mPreservedParams)); } /** * Restores original dimensions after they were changed for percentage based values. * You should call this method only if you previously called * {@link PercentLayoutHelper.PercentLayoutInfo#fillLayoutParams(ViewGroup.LayoutParams, int, int)}. */ public void restoreLayoutParams(ViewGroup.LayoutParams params) { if (!mPreservedParams.mIsWidthComputedFromAspectRatio) { // Only restore the width if we didn't compute it based on the height and // aspect ratio in the fill pass. params.width = mPreservedParams.width; } if (!mPreservedParams.mIsHeightComputedFromAspectRatio) { // Only restore the height if we didn't compute it based on the width and // aspect ratio in the fill pass. params.height = mPreservedParams.height; } // Reset the tracking flags. mPreservedParams.mIsWidthComputedFromAspectRatio = false; mPreservedParams.mIsHeightComputedFromAspectRatio = false; } } /** * If a layout wants to support percentage based dimensions and use this helper class, its * {@code LayoutParams} subclass must implement this interface. * * Your {@code LayoutParams} subclass should contain an instance of {@code PercentLayoutInfo} * and the implementation of this interface should be a simple accessor. */ public interface PercentLayoutParams { PercentLayoutInfo getPercentLayoutInfo(); } }