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Validating ViewPager Change Listener Generation in ButterKnife

This test suite validates the OnPageChange functionality in ButterKnife’s view binding system, specifically focusing on ViewPager integration and event handling. It ensures proper generation of binding code for page change listeners and cleanup.

Test Coverage Overview

The test suite covers ViewPager page change event binding functionality, verifying correct code generation for the @OnPageChange annotation.

Key areas tested include:

Proper listener implementation generation
Correct method binding for page selection events
Proper cleanup and unbinding of listeners
Integration with AndroidX ViewPager components

Implementation Analysis

The testing approach uses compile-time verification to ensure proper code generation. It employs a combination of source code comparison and compilation validation.

Technical implementation includes:

JavaFileObjects for source and expected output comparison
Annotation processing verification
Compile-time error checking
Generated binding class structure validation

Technical Details

Testing tools and configuration:

ButterKnifeProcessor for annotation processing
Google Truth assertion framework
JavaSourcesSubjectFactory for source compilation testing
Custom compiler options for processing validation
AndroidX ViewPager test stubs

Best Practices Demonstrated

The test demonstrates high-quality testing practices for annotation processors and code generation.

Notable practices include:

Explicit verification of generated code structure
Comprehensive lifecycle management testing
Clean separation of test sources and expected outputs
Proper handling of Android framework dependencies

jakewharton/butterknife

butterknife-runtime/src/test/java/butterknife/OnPageChangeTest.java

            
package butterknife;

import butterknife.compiler.ButterKnifeProcessor;
import com.google.testing.compile.JavaFileObjects;
import javax.tools.JavaFileObject;
import org.junit.Test;

import static butterknife.TestStubs.ANDROIDX_VIEW_PAGER;
import static com.google.common.truth.Truth.assertAbout;
import static com.google.testing.compile.JavaSourcesSubjectFactory.javaSources;
import static java.util.Arrays.asList;

public class OnPageChangeTest {
  @Test public void pageChange() {
    JavaFileObject source = JavaFileObjects.forSourceString("test.Test", ""
        + "package test;\n"
        + "import butterknife.OnPageChange;\n"
        + "public class Test {\n"
        + "  @OnPageChange(1) void doStuff() {}\n"
        + "}"
    );

    JavaFileObject bindingSource = JavaFileObjects.forSourceString("test/Test_ViewBinding", ""
        + "package test;\n"
        + "import android.view.View;\n"
        + "import androidx.annotation.CallSuper;\n"
        + "import androidx.annotation.UiThread;\n"
        + "import androidx.viewpager.widget.ViewPager;\n"
        + "import butterknife.Unbinder;\n"
        + "import butterknife.internal.Utils;\n"
        + "import java.lang.IllegalStateException;\n"
        + "import java.lang.Override;\n"
        + "public class Test_ViewBinding implements Unbinder {\n"
        + "  private Test target;\n"
        + "  private View view1;\n"
        + "  private ViewPager.OnPageChangeListener view1OnPageChangeListener;\n"
        + "  @UiThread\n"
        + "  public Test_ViewBinding(final Test target, View source) {\n"
        + "    this.target = target;\n"
        + "    View view;\n"
        + "    view = Utils.findRequiredView(source, 1, \"method 'doStuff'\");\n"
        + "    view1 = view;\n"
        + "    view1OnPageChangeListener = new ViewPager.OnPageChangeListener() {\n"
        + "      @Override\n"
        + "      public void onPageSelected(int p0) {\n"
        + "        target.doStuff();\n"
        + "      }\n"
        + "      @Override\n"
        + "      public void onPageScrolled(int p0, float p1, int p2) {\n"
        + "      }\n"
        + "      @Override\n"
        + "      public void onPageScrollStateChanged(int p0) {\n"
        + "      }\n"
        + "    };\n"
        + "    ((ViewPager) view).addOnPageChangeListener(view1OnPageChangeListener);\n"
        + "  }\n"
        + "  @Override\n"
        + "  @CallSuper\n"
        + "  public void unbind() {\n"
        + "    if (target == null) throw new IllegalStateException(\"Bindings already cleared.\");\n"
        + "    target = null;\n"
        + "    ((ViewPager) view1).removeOnPageChangeListener(view1OnPageChangeListener);\n"
        + "    view1OnPageChangeListener = null;\n"
        + "    view1 = null;\n"
        + "  }\n"
        + "}"
    );

    assertAbout(javaSources())
        .that(asList(source, ANDROIDX_VIEW_PAGER))
        .withCompilerOptions("-Xlint:-processing")
        .processedWith(new ButterKnifeProcessor())
        .compilesWithoutWarnings()
        .and()
        .generatesSources(bindingSource);
  }
}