This example will show you how to use various android.graphics.Canvas class’s methods to draw text, point, line, circle, rectangle, oval, arc, and self-defined shapes.
1. Android Graphics Canvas Draw Method Example.
If you can not watch the above video, you can see it on the youtube URL https://youtu.be/HtR0yY0kCcI
- The above example demo video shows that we can choose the canvas draw method from the drop-down spinner view list.
- After select one, the app will use that method to draw a shape or text in the below custom view.
2. Android Canvas Draw Method Example Source Code.
- Below are the example android project files.
C:\WORKSPACE\WORK\DEV2QA.COM-EXAMPLE-CODE\ANDROIDEXAMPLEPROJECT\CANVASPAINT │ .gitignore │ build.gradle │ gradle.properties │ gradlew │ gradlew.bat │ settings.gradle │ ├───.idea │ gradle.xml │ misc.xml │ modules.xml │ runConfigurations.xml │ ├───app │ │ .gitignore │ │ build.gradle │ │ proguard-rules.pro │ │ │ └───src │ ├───androidTest │ │ └───java │ │ └───com │ │ └───dev2qa │ │ └───canvaspaint │ │ ExampleInstrumentedTest.java │ │ │ ├───main │ │ │ AndroidManifest.xml │ │ │ │ │ ├───java │ │ │ └───com │ │ │ └───dev2qa │ │ │ └───canvaspaint │ │ │ CanvasExampleView.java │ │ │ ConstantsUtil.java │ │ │ MainActivity.java │ │ │ test.java │ │ │ │ │ └───res │ │ ├───drawable │ │ │ ic_launcher_background.xml │ │ │ │ │ ├───drawable-v24 │ │ │ ic_launcher_foreground.xml │ │ │ │ │ ├───layout │ │ │ activity_main.xml │ │ │ layout.xml │ │ │ │ │ ├───mipmap-anydpi-v26 │ │ │ ic_launcher.xml │ │ │ ic_launcher_round.xml │ │ │ │ │ ├───mipmap-hdpi │ │ │ ic_launcher.png │ │ │ ic_launcher_round.png │ │ │ │ │ ├───mipmap-mdpi │ │ │ ic_launcher.png │ │ │ ic_launcher_round.png │ │ │ │ │ ├───mipmap-xhdpi │ │ │ ic_launcher.png │ │ │ ic_launcher_round.png │ │ │ │ │ ├───mipmap-xxhdpi │ │ │ ic_launcher.png │ │ │ ic_launcher_round.png │ │ │ │ │ ├───mipmap-xxxhdpi │ │ │ ic_launcher.png │ │ │ ic_launcher_round.png │ │ │ │ │ └───values │ │ arrays.xml │ │ colors.xml │ │ strings.xml │ │ styles.xml │ │ │ └───test │ └───java │ └───com │ └───dev2qa │ └───canvaspaint │ ExampleUnitTest.java │ └───gradle └───wrapper gradle-wrapper.jar gradle-wrapper.properties - There are six core files in this example.
- MainActivity.java
- CanvasExampleView.java
- ConstantsUtil.java
- activity_main.xml
- arrays.xml
- strings.xml
2.1 Main Activity Java Class.
- MainActivity.java
package com.dev2qa.canvaspaint; import android.content.Context; import android.content.res.Resources; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.AdapterView; import android.widget.Button; import android.widget.LinearLayout; import android.widget.Spinner; public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); setTitle("dev2qa.com - Android Canvas Paint Drawing Example."); final Context context = getApplicationContext(); final LinearLayout drawingExampleLayout = (LinearLayout)findViewById(R.id.exampleLinearLayout); // Must declare the custom view here, otherwise the custom view's onDraw method will not be invoked after call invalidate method. final CanvasExampleView canvasExampleView = new CanvasExampleView(context); final Resources resources = getResources(); /* Get canvas spinner and set it's on item selected listener. */ Spinner canvasSpinner = (Spinner)findViewById(R.id.canvasSpinner); canvasSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() { @Override public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) { // Remove all views first. drawingExampleLayout.removeAllViews(); // Add custom canvasExampleView. drawingExampleLayout.addView(canvasExampleView); Object selectedItemObj = adapterView.getAdapter().getItem(i); String itemText = (String)selectedItemObj; if(itemText.equals(resources.getString(R.string.draw_text))) { canvasExampleView.drawText(); }else if(itemText.equals(resources.getString(R.string.draw_point))) { canvasExampleView.drawPoint(); }else if(itemText.equals(resources.getString(R.string.draw_two_point))) { canvasExampleView.drawTwoPoint(); }else if(itemText.equals(resources.getString(R.string.draw_line))) { canvasExampleView.drawLine(); }else if(itemText.equals(resources.getString(R.string.draw_two_line))) { canvasExampleView.drawTwoLine(); }else if(itemText.equals(resources.getString(R.string.draw_rectangle))) { canvasExampleView.drawRectangle(); }else if(itemText.equals(resources.getString(R.string.draw_round_rectangle))) { canvasExampleView.drawRoundRectangle(); }else if(itemText.equals(resources.getString(R.string.draw_arc))) { canvasExampleView.drawArc(); }else if(itemText.equals(resources.getString(R.string.draw_oval))) { canvasExampleView.drawOval(); }else if(itemText.equals(resources.getString(R.string.draw_path))) { canvasExampleView.drawPath(); }else if(itemText.equals(resources.getString(R.string.draw_circle_path_text))) { canvasExampleView.drawCirclePathText(); }else if(itemText.equals(resources.getString(R.string.draw_circle))) { canvasExampleView.drawCircle(); } } @Override public void onNothingSelected(AdapterView<?> adapterView) { } }); } }
2.2 Custom View Java Class.
- CanvasExampleView.java
package com.dev2qa.canvaspaint; import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.RectF; import android.graphics.Path; import android.view.View; public class CanvasExampleView extends View { private String action = ""; public CanvasExampleView(Context context) { super(context); setFocusable(true); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); Paint paint = new Paint(); paint.setTextSize(100); paint.setColor(Color.GREEN); // Set the point, line width. If do not set this, the point is too small to see, the line is too thin also. paint.setStrokeWidth(30); // Fill out the background color to refresh the screen. canvas.drawColor(Color.BLUE); if(ConstantsUtil.DRAW_POINT.equals(action)) { // Draw one point in pixel. canvas.drawPoint(100, 200, paint); }else if(ConstantsUtil.DRAW_TWO_POINT.equals(action)) { // Draw multiple points ( two point ) in pixel. float pointsArray[] = {180, 260, 260, 300}; canvas.drawPoints(pointsArray, paint); }else if(ConstantsUtil.DRAW_ARC.equals(action)) { RectF rectF = new RectF(100, 200, 800, 900); paint.setAlpha(0x88); canvas.drawArc(rectF, 30, 100, true, paint); }else if(ConstantsUtil.DRAW_CIRCLE.equals(action)) { // Draw a circle. canvas.drawCircle(600,800, 600, paint); }else if(ConstantsUtil.DRAW_CIRCLE_PATH_TEXT.equals(action)) { Path arcPath = new Path(); arcPath.addCircle(500, 800, 600, Path.Direction.CW); canvas.drawTextOnPath("dev2qa.com", arcPath, 600, 0, paint); }else if(ConstantsUtil.DRAW_LINE.equals(action)) { // Draw the long line. canvas.drawLine(100, 500, 1000, 510, paint); }else if(ConstantsUtil.DRAW_OVAL.equals(action)) { paint.setARGB(0x77, 0x11, 0x00, 0x66); RectF rectF = new RectF(100, 200, 800, 800); canvas.drawOval(rectF, paint); }else if(ConstantsUtil.DRAW_PATH.equals(action)) { Path path = new Path(); // Set start point. path.moveTo(100, 200); // Path one. path.lineTo(500, 800); // Path two. path.lineTo(300, 1000); // Path complete. path.close(); canvas.drawPath(path, paint); }else if(ConstantsUtil.DRAW_RECTANGLE.equals(action)) { paint.setStyle(Paint.Style.STROKE); // Draw rectangle canvas.drawRect(100, 1000, 800, 1300, paint); }else if(ConstantsUtil.DRAW_ROUND_RECTANGLE.equals(action)) { RectF rectF = new RectF(100, 200, 800, 1000); canvas.drawRoundRect(rectF, 100, 200, paint); }else if(ConstantsUtil.DRAW_TEXT.equals(action)) { paint.setTextAlign(Paint.Align.CENTER); // Draw text. canvas.drawText("dev2qa.com", 600, 600, paint); }else if(ConstantsUtil.DRAW_TWO_LINE.equals(action)) { // Draw two short lines. float linePointsArray[] = {10, 550, 120, 600, 280, 650, 800,610}; canvas.drawLines(linePointsArray, paint); } } public void drawPoint() { action = ConstantsUtil.DRAW_POINT; invalidate(); } public void drawTwoPoint() { action = ConstantsUtil.DRAW_TWO_POINT; invalidate(); } public void drawLine() { action = ConstantsUtil.DRAW_LINE; invalidate(); } public void drawTwoLine() { action = ConstantsUtil.DRAW_TWO_LINE; invalidate(); } public void drawCircle() { action = ConstantsUtil.DRAW_CIRCLE; invalidate(); } public void drawCirclePathText() { action = ConstantsUtil.DRAW_CIRCLE_PATH_TEXT; invalidate(); } public void drawRectangle() { action = ConstantsUtil.DRAW_RECTANGLE; invalidate(); } public void drawRoundRectangle() { action = ConstantsUtil.DRAW_ROUND_RECTANGLE; invalidate(); } public void drawOval() { action = ConstantsUtil.DRAW_OVAL; invalidate(); } public void drawArc() { action = ConstantsUtil.DRAW_ARC; invalidate(); } public void drawPath() { action = ConstantsUtil.DRAW_PATH; invalidate(); } public void drawText() { action = ConstantsUtil.DRAW_TEXT; invalidate(); } }
2.3 Constant Util Java Class.
- ConstantsUtil.java
package com.dev2qa.canvaspaint; public class ConstantsUtil { public static String DRAW_TEXT = "DRAW_TEXT"; public static String DRAW_POINT = "DRAW_POINT"; public static String DRAW_TWO_POINT = "DRAW_TWO_POINT"; public static String DRAW_LINE = "DRAW_LINE"; public static String DRAW_TWO_LINE = "DRAW_TWO_LINE"; public static String DRAW_CIRCLE = "DRAW_CIRCLE"; public static String DRAW_RECTANGLE = "DRAW_RECTANGLE"; public static String DRAW_ROUND_RECTANGLE = "DRAW_ROUND_RECTANGLE"; public static String DRAW_ARC = "DRAW_ARC"; public static String DRAW_OVAL = "DRAW_OVAL"; public static String DRAW_PATH = "DRAW_PATH"; public static String DRAW_CIRCLE_PATH_TEXT = "DRAW_CIRCLE_PATH_TEXT"; }
2.4 Main Activity Layout Xml File.
- app / res / layout / activity_main.xml
<TableLayout android:padding="20dp" android:layout_width="match_parent" android:layout_height="match_parent"> <TableRow android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center_horizontal" android:orientation="horizontal"> <TextView android:gravity="end" android:text="Canvas Function : " /> <Spinner android:id="@+id/canvasSpinner" android:layout_width="wrap_content" android:layout_height="wrap_content" android:entries="@array/canvas_function" android:spinnerMode="dropdown"/> </TableRow> <TableRow android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center_horizontal" android:orientation="horizontal"> <LinearLayout android:id="@+id/exampleLinearLayout" android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical" android:layout_span="2" /> </TableRow> </TableLayout>
2.5 Resource Arrays Definition Xml File.
- app / res / values / arrays.xml
<?xml version="1.0" encoding="utf-8"?> <resources> <!-- Canvas function spinner items. --> <string-array name="canvas_function"> <item>@string/select_function</item> <item>@string/draw_text</item> <item>@string/draw_point</item> <item>@string/draw_two_point</item> <item>@string/draw_line</item> <item>@string/draw_two_line</item> <item>@string/draw_circle</item> <item>@string/draw_rectangle</item> <item>@string/draw_round_rectangle</item> <item>@string/draw_arc</item> <item>@string/draw_oval</item> <item>@string/draw_path</item> <item>@string/draw_circle_path_text</item> </string-array> </resources>
2.6 Resource Strings Definition Xml File.
- app / res / values / strings.xml
<resources> <string name="app_name">CanvasPaint</string> <string name="select_function">Select Function</string> <!-- Canvas drawing function example string.--> <string name="draw_text">Draw Text</string> <string name="draw_point">Draw Point</string> <string name="draw_two_point">Draw Two Point</string> <string name="draw_line">Draw Line</string> <string name="draw_two_line">Draw Two Line</string> <string name="draw_circle">Draw Circle</string> <string name="draw_rectangle">Draw Rectangle</string> <string name="draw_round_rectangle">Draw Round Rectangle</string> <string name="draw_arc">Draw Arc</string> <string name="draw_oval">Draw Oval</string> <string name="draw_path">Draw Path</string> <string name="draw_circle_path_text">Draw Circle Path Text</string> </resources>
