[android] Fix issues with sensor time series graph (project-chip#8933)

1. Round values on the Y axis.
2. Make sure the viewport of the graph widget is correctly
   updated with each new sensor measumrent.

src/android/CHIPTool/app/src/main/java/com/google/chip/chiptool/clusterclient/SensorClientFragment.kt

@@ -22,7 +22,6 @@ import kotlinx.android.synthetic.main.sensor_client_fragment.view.*
 import kotlinx.coroutines.*
 import java.text.SimpleDateFormat
 import java.util.*
-import kotlin.concurrent.schedule
 
 private typealias ReadCallback = ChipClusters.IntegerAttributeCallback
 
@@ -56,15 +55,20 @@ class SensorClientFragment : Fragment() {
           watchSensorButtonUnchecked()
         }
       }
+      val currentTime = Calendar.getInstance().time.time
       sensorGraph.addSeries(sensorData)
-      sensorGraph.gridLabelRenderer.padding = 30
+      sensorGraph.viewport.isXAxisBoundsManual = true
+      sensorGraph.viewport.setMinX(currentTime.toDouble())
+      sensorGraph.viewport.setMaxX(currentTime.toDouble() + REFRESH_PERIOD_MS * MAX_DATA_POINTS)
+      sensorGraph.gridLabelRenderer.padding = 20
       sensorGraph.gridLabelRenderer.numHorizontalLabels = 4
+      sensorGraph.gridLabelRenderer.setHorizontalLabelsAngle(150)
       sensorGraph.gridLabelRenderer.labelFormatter = object : LabelFormatter {
         override fun setViewport(viewport: Viewport?) = Unit
         override fun formatLabel(value: Double, isValueX: Boolean): String {
           if (!isValueX)
-            return value.toString()
-          return SimpleDateFormat("H:m:s").format(Date(value.toLong())).toString()
+            return "%.2f".format(value)
+          return SimpleDateFormat("H:mm:ss").format(Date(value.toLong())).toString()
         }
       }
     }
@@ -151,11 +155,16 @@ class SensorClientFragment : Fragment() {
       )
 
       if (addToGraph) {
-        // Make the graph visible on the first sample
-        if (sensorData.isEmpty)
-          sensorGraph.visibility = View.VISIBLE
+        val isFirstSample = sensorData.isEmpty
         val dataPoint = DataPoint(Calendar.getInstance().time, value)
-        sensorData.appendData(dataPoint, false, MAX_DATA_POINTS)
+        sensorData.appendData(dataPoint, true, MAX_DATA_POINTS)
+        if (isFirstSample) {
+          // Make the graph visible on the first sample. Also, workaround a bug in graphview
+          // related to calculating the viewport when there is only one data point by
+          // duplicating the first sample.
+          sensorData.appendData(dataPoint, true, MAX_DATA_POINTS)
+          sensorGraph.visibility = View.VISIBLE
+        }
       }
     }
   }

src/android/CHIPTool/app/src/main/res/layout/sensor_client_fragment.xml

@@ -95,7 +95,7 @@
         <com.jjoe64.graphview.GraphView
             android:id="@+id/sensorGraph"
             android:layout_width="match_parent"
-            android:layout_height="100dp"
+            android:layout_height="150dp"
             android:layout_below="@+id/lastValueTv"
             android:layout_marginTop="16dp"
             android:layout_marginStart="16dp"

src/android/CHIPTool/app/src/main/res/values/strings.xml

@@ -79,7 +79,7 @@
     <string name="sensor_client_btn_text">Sensor clusters</string>
     <string name="sensor_client_read_btn_text">Read</string>
     <string name="sensor_client_watch_btn_text">Watch</string>
-    <string name="sensor_client_last_value_text">Last value: %1$.1f %2$s</string>
+    <string name="sensor_client_last_value_text">Last value: %1$.2f %2$s</string>
     <string name="sensor_client_read_error_text">Failed to read the sensor: %1$s</string>
 
 </resources>