6.8.4. Overriding View Method onSizeChanged

Figure 6.10 overrides class View’s onSizeChanged method, which is called whenever the View’s size changes, including when the View is first added to the View hierarchy as the layout is inflated. This app always displays in portrait mode, so onSizeChanged is called only once when the activity’s onCreate method inflates the GUI. The method receives the View’s new width and height and its old width and height—when this method is called the first time, the old width and height are 0. The calculations performed here scale the game’s on-screen elements based on the device’s pixel width and height. We arrived at our scaling factors via trial and error, choosing values that made the game elements look nice on the screen. Lines 170–175 configure the Paint objects that are used to specify drawing characteristics for the game’s elements. After the calculations, line 177 calls method newGame (Fig. 6.11).

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132      // called by surfaceChanged when the size of the SurfaceView changes,
133      // such as when it's first added to the View hierarchy
134      @Override
135      protected void onSizeChanged(int w, int h, int oldw, int oldh)
136      {
137         super.onSizeChanged(w, h, oldw, oldh);
138
139         screenWidth = w; // store CannonView's width
140         screenHeight = h; // store CannonView's height
141         cannonBaseRadius = h / 18; // cannon base radius 1/18 screen height
142         cannonLength = w / 8; // cannon length 1/8 screen width
143
144         cannonballRadius = w / 36; // cannonball radius 1/36 screen width
145         cannonballSpeed = w * 3 / 2; // cannonball speed multiplier
146
147         lineWidth = w / 24; // target and blocker 1/24 screen width
148
149         // configure instance variables related to the blocker
150         blockerDistance = w * 5 / 8; // blocker 5/8 screen width from left
151         blockerBeginning = h / 8; // distance from top 1/8 screen height
152         blockerEnd = h * 3 / 8 ; // distance from top 3/8 screen height
153         initialBlockerVelocity = h / 2; // initial blocker speed multiplier
154         blocker.start = new Point(blockerDistance, blockerBeginning);
155         blocker.end = new Point(blockerDistance, blockerEnd);
156
157         // configure instance variables related to the target
158         targetDistance = w * 7 / 8; // target 7/8 screen width from left
159         targetBeginning = h / 8 ; // distance from top 1/8 screen height
160         targetEnd = h * 7 / 8; // distance from top 7/8 screen height
161         pieceLength = (targetEnd - targetBeginning) / TARGET_PIECES;
162         initialTargetVelocity = -h / 4; // initial target speed multiplier
163         target.start = new Point(targetDistance, targetBeginning);
164         target.end = new Point(targetDistance, targetEnd);
165
166         // endpoint of the cannon's barrel initially points horizontally
167         barrelEnd = new Point(cannonLength, h / 2);
168
169         // configure Paint objects for drawing game elements
170         textPaint.setTextSize(w / 20); // text size 1/20 of screen width   
171         textPaint.setAntiAlias(true); // smoothes the text                 
172         cannonPaint.setStrokeWidth(lineWidth * 1.5f); // set line thickness
173         blockerPaint.setStrokeWidth(lineWidth); // set line thickness      
174         targetPaint.setStrokeWidth(lineWidth); // set line thickness       
175         backgroundPaint.setColor(Color.WHITE); // set background color     
176
177         newGame(); // set up and start a new game
178      } // end method onSizeChanged
179

Fig. 6.10 | Overridden onSizeChanged method.